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Hansson E, Jakobsson K, Glaser J, Wesseling C, Chavarria D, Lucas RAI, Prince H, Wegman DH. Impact of heat and a rest-shade-hydration intervention program on productivity of piece-paid industrial agricultural workers at risk of chronic kidney disease of nontraditional origin. Ann Work Expo Health 2024; 68:366-375. [PMID: 38367206 PMCID: PMC11033565 DOI: 10.1093/annweh/wxae007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2023] [Accepted: 02/06/2024] [Indexed: 02/19/2024] Open
Abstract
OBJECTIVES Assess the impact of environmental heat and a rest-shade-hydration (RSH) intervention against heat stress on productivity of piece-paid Mesoamerican sugarcane cutters. These workers are at a high risk of chronic kidney disease of non-traditional origin (CKDnt), from the severe heat stress they experience due to heavy work under hot conditions. RSH interventions in these populations improve kidney health outcomes, but their impact on productivity has yet to be examined. METHODS We accessed routine productivity data from seed (SC, N = 749) and burned (BCC, N = 535) sugarcane cutters observed over five harvest seasons with increasing RSH intervention at a large Nicaraguan sugarcane mill. Hourly field-site wet-bulb globe temperature (WBGT) was recorded by mill staff and summarized as a daily mean. Mixed linear regression was used to model daily productivity, adjusting for age (18-29, 30-44, and >45 years), sex, WBGT (<28, 28-29, 29-30, 30-31, and >31 °C) on the same and preceding day, harvest season (2017-18 to 2021-22), month, and acclimatization status (<1, 1-2, and >2 weeks). RESULTS There was an inverse dose-response relationship between SC productivity and WBGT on the same and preceding days, decreasing by approximately 3%/°C WBGT. Productivity increased during the study period, i.e. coinciding with RSH scale-up, by approximately 19% in SC and 9% in BCC. CONCLUSION Agricultural worker productivity was expected lower on hotter days, strengthening the interest in all stakeholders to mitigate increasing global temperatures and their impact. Despite decreasing the total time allocated for work each day, an RSH intervention appears to result in increased productivity and no apparent loss in productivity.
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Affiliation(s)
- Erik Hansson
- La Isla Network, 2219 California NW Unit 52, 20008 Washington, District of Columbia, United States
- Occupational and Environmental Medicine, School of Public Health and Community Medicine, Sahlgrenska Academy, University of Gothenburg, Box 414, 413 90 Gothenburg, Sweden
| | - Kristina Jakobsson
- La Isla Network, 2219 California NW Unit 52, 20008 Washington, District of Columbia, United States
- Occupational and Environmental Medicine, School of Public Health and Community Medicine, Sahlgrenska Academy, University of Gothenburg, Box 414, 413 90 Gothenburg, Sweden
- Occupational and Environmental Medicine, Sahlgrenska University Hospital, Box 414, 413 90 Gothenburg, Sweden
| | - Jason Glaser
- La Isla Network, 2219 California NW Unit 52, 20008 Washington, District of Columbia, United States
| | - Catharina Wesseling
- La Isla Network, 2219 California NW Unit 52, 20008 Washington, District of Columbia, United States
- Unit of Occupational Medicine, Institute of Environmental Medicine, Karolinska Institute, Box 210, 171 77 Stockholm, Sweden
| | - Denis Chavarria
- Occupational Health Management, Ingenio San Antonio/Nicaragua Sugar Estates Limited, Km. 119 Carretera León-Chinandega, Chichigalpa, Nicaragua
| | - Rebekah A I Lucas
- La Isla Network, 2219 California NW Unit 52, 20008 Washington, District of Columbia, United States
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham B15 2TT, United Kingdom
| | - Heath Prince
- La Isla Network, 2219 California NW Unit 52, 20008 Washington, District of Columbia, United States
- LBJ School of Public Affairs, University of Texas at Austin, 2315 Red River St, Austin, TX 78712,United States
| | - David H Wegman
- La Isla Network, 2219 California NW Unit 52, 20008 Washington, District of Columbia, United States
- University of Massachusetts Lowell, 1 University Avenue, Lowell, 01854 MA, United States
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Hansson E, Jakobsson K, Glaser JR, Wesseling C, Chavarría D, Lucas RAI, Wegman DH. Association Between Acute Kidney Injury Hospital Visits and Environmental Heat Stress at a Nicaraguan Sugarcane Plantation. Workplace Health Saf 2024:21650799241235410. [PMID: 38591368 DOI: 10.1177/21650799241235410] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/10/2024]
Abstract
BACKGROUND Mesoamerican sugarcane cutters are at a high risk of chronic kidney disease of non-traditional origin, a disease likely linked to heat-related acute kidney injury (AKI). Studies in general populations have described a positive association between high environmental temperatures and clinically assessed kidney outcomes, but there are no studies in occupational settings. METHOD We accessed routine records of clinically diagnosed AKI (AKI-CD) and wet bulb globe temperatures (WBGT) at a large Nicaraguan sugarcane plantation and modeled the relationship between these using negative binomial regression. A rest-shade-hydration intervention was gradually enhanced during the study period, and efforts were made to increase the referral of workers with suspected AKI to healthcare. RESULTS Each 1°C WBGT was associated with an 18% (95% confidence interval [CI]: [4, 33%]) higher AKI-CD rate on the same day and a 14% (95% CI [-5, 37%]) higher rate over a week. AKI-CD rates and severity, and time between symptoms onset and diagnosis decreased during the study period, that is, with increasing rest-shade-hydration intervention. Symptoms and biochemical signs of systemic inflammation were common among AKI-CD cases. DISCUSSION Occupational heat stress, resulting from heavy work in environmental heat, was associated with a higher rate of clinically diagnosed AKI in a population at risk of CKDnt. Promoting rest-shade-hydration may have contributed to reducing AKI rates during the study period. Occupational health and safety personnel have key roles to play in enforcing rest, shade, and hydration practices, referring workers with suspected AKI to healthcare as well as collecting and analyzing the data needed to support workplace heat stress interventions.
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Affiliation(s)
- Erik Hansson
- La Isla Network, Washington, District of Columbia, USA
- Occupational and Environmental Medicine, School of Public Health and Community Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Kristina Jakobsson
- La Isla Network, Washington, District of Columbia, USA
- Occupational and Environmental Medicine, School of Public Health and Community Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
- Occupational and Environmental Medicine, Sahlgrenska University Hospital, Gothenburg, Sweden
| | | | - Catharina Wesseling
- La Isla Network, Washington, District of Columbia, USA
- Unit of Occupational Medicine, Institute of Environmental Medicine, Karolinska Institute, Stockholm, Sweden
| | - Denis Chavarría
- Occupational Health Management, Ingenio San Antonio/Nicaragua Sugar Estates Limited, Chichigalpa, Nicaragua
| | - Rebekah A I Lucas
- La Isla Network, Washington, District of Columbia, USA
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK
| | - David H Wegman
- La Isla Network, Washington, District of Columbia, USA
- University of Massachusetts Lowell, Lowell, Massachusetts, USA
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Skinner BD, Lucas RAI, Lucas SJE. Exposure to passive heat and cold stress differentially modulates cerebrovascular-CO 2 responsiveness. J Appl Physiol (1985) 2024; 136:23-32. [PMID: 37969086 DOI: 10.1152/japplphysiol.00494.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2023] [Revised: 10/30/2023] [Accepted: 11/13/2023] [Indexed: 11/17/2023] Open
Abstract
Heat and cold stress influence cerebral blood flow (CBF) regulatory factors (e.g., arterial CO2 partial pressure). However, it is unclear whether the CBF response to a CO2 stimulus (i.e., cerebrovascular-CO2 responsiveness) is maintained under different thermal conditions. This study aimed to compare cerebrovascular-CO2 responsiveness between normothermia, passive heat, and cold stress conditions. Sixteen participants (8 females; 25 ± 7 yr) completed two experimental sessions (randomized) comprising normothermic and either passive heat or cold stress conditions. Middle and posterior cerebral artery velocity (MCAv, PCAv) were measured during rest, hypercapnia (5% CO2 inhalation), and hypocapnia (voluntary hyperventilation to an end-tidal CO2 of 30 mmHg). The linear slope of the cerebral blood velocity (CBv) response to changing end-tidal CO2 was calculated to measure cerebrovascular-CO2 responsiveness, and cerebrovascular conductance (CVC) was used to examine responsiveness independent of blood pressure. CBv-CVC-CO2 responsiveness to hypocapnia was greater during heat stress compared with cold stress (MCA: +0.05 ± 0.08 cm/s/mmHg/mmHg, P = 0.04; PCA: +0.02 ± 0.02 cm/s/mmHg/mmHg, P = 0.002). CBv-CO2 responsiveness to hypercapnia decreased during heat stress (MCA: -0.67 ± 0.89 cm/s/mmHg, P = 0.02; PCA: -0.64 ± 0.62 cm/s/mmHg; P = 0.01) and increased during cold stress (MCA: +0.98 ± 1.33 cm/s/mmHg, P = 0.03; PCA: +1.00 ± 0.82 cm/s/mmHg; P = 0.01) compared with normothermia. However, CBv-CVC-CO2 responsiveness to hypercapnia was not different between thermal conditions (P > 0.08). Overall, passive heat, but not cold, stress challenges the maintenance of cerebral perfusion. A greater cerebrovascular responsiveness to hypocapnia during heat stress likely reduces an already impaired cerebrovascular reserve capacity and may contribute to adverse events (e.g., syncope).NEW & NOTEWORTHY This study demonstrates that thermoregulatory-driven perfusion pressure changes, from either cold or heat stress, impact cerebrovascular responsiveness to hypercapnia. Compared with cold stress, heat stress poses a greater challenge to the maintenance of cerebral perfusion during hypocapnia, challenging cerebrovascular reserve capacity while increasing cerebrovascular-CO2 responsiveness. This likely exacerbates cerebral hypoperfusion during heat stress since hyperthermia-induced hyperventilation results in hypocapnia. No regional differences in middle and posterior cerebral artery responsiveness were found with thermal stress.
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Affiliation(s)
- Bethany D Skinner
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Rebekah A I Lucas
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Samuel J E Lucas
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom
- Centre for Human Brain Health, University of Birmingham, Birmingham, United Kingdom
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Skinner BD, Weaver SRC, Lucas SJE, Lucas RAI. Menstrual phase influences cerebrovascular responsiveness in females but may not affect sex differences. Front Physiol 2023; 13:1035452. [PMID: 36685202 PMCID: PMC9846518 DOI: 10.3389/fphys.2022.1035452] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2022] [Accepted: 12/13/2022] [Indexed: 01/06/2023] Open
Abstract
Background and aims: Sex differences in the rate and occurrence of cerebrovascular diseases (e.g., stroke) indicate a role for female sex hormones (i.e., oestrogen and progesterone) in cerebrovascular function and regulation. However, it remains unclear how cerebrovascular function differs between the sexes, and between distinct phases of the menstrual cycle. This study aimed to compare cerebrovascular-CO2 responsiveness in 1) females during the early follicular (EF), ovulatory (O) and mid-luteal (ML) phases of their menstrual cycle; and 2) males compared to females during phases of lower oestrogen (EF) and higher oestrogen (O). Methods: Eleven females (25 ± 5 years) complete experimental sessions in the EF (n = 11), O (n = 9) and ML (n = 11) phases of the menstrual cycle. Nine males (22 ± 3 years) completed two experimental sessions, approximately 2 weeks apart for comparison to females. Middle and posterior cerebral artery velocity (MCAv, PCAv) was measured at rest, during two stages of hypercapnia (2% and 5% CO2 inhalation) and hypocapnia (voluntary hyperventilation to an end-tidal CO2 of 30 and 24 mmHg). The linear slope of the cerebral blood velocity response to changes in end-tidal CO2 was calculated to measure cerebrovascular-CO2 responsiveness.. Results: In females, MCAv-CO2 responsiveness to hypocapnia was lower during EF (-.78 ± .45 cm/s/mmHg) when compared to the O phase (-1.17 ± .52 cm/s/mmHg; p < .05) and the ML phase (-1.30 ± .82; p < .05). MCAv-CO2 responsiveness to hypercapnia and hypo-to-hypercapnia, and PCAv-CO2 responsiveness across the CO2 range were similar between menstrual phases (p ≥ .20). MCAv-CO2 responsiveness to hypo-to hypercapnia was greater in females compared to males (3.12 ± .91 cm/s/mmHg vs. 2.31 ± .46 cm/s/mmHg; p = .03), irrespective of menstrual phase (EF or O). Conclusion: Females during O and ML phases have an enhanced vasoconstrictive capacity of the MCA compared to the EF phase. Additionally, biological sex differences can influence cerebrovascular-CO2 responsiveness, dependent on the insonated vessel.
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Affiliation(s)
- Bethany D. Skinner
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom,Centre for Human Brain Health, University of Birmingham, Edgbaston, Birmingham, United Kingdom,*Correspondence: Bethany D. Skinner,
| | - Samuel R. C. Weaver
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom,Centre for Human Brain Health, University of Birmingham, Edgbaston, Birmingham, United Kingdom
| | - Samuel J. E. Lucas
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom,Centre for Human Brain Health, University of Birmingham, Edgbaston, Birmingham, United Kingdom
| | - Rebekah A. I. Lucas
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom
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Lucas RAI, Skinner BD, Arias-Monge E, Jakobsson K, Wesseling C, Weiss I, Poveda S, Cerda-Granados FI, Glaser J, Hansson E, Wegman DH. Targeting workload to ameliorate risk of heat stress in industrial sugarcane workers. Scand J Work Environ Health 2023; 49:43-52. [PMID: 36209512 PMCID: PMC10549916 DOI: 10.5271/sjweh.4057] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Indexed: 12/31/2022] Open
Abstract
OBJECTIVE The aim of this study was to quantify the physiological workload of manual laborers in industrial sugarcane and assess the effect of receiving a rest, shade, and hydration intervention to reduce heat stress exposure risk. METHODS In an observational study, physiological workload was evaluated for burned cane cutters (BCC), seed cutters (SC) and drip irrigation repair workers (DIRW) using heart rate (HR) recorded continuously (Polar®) across a work shift. Workers' percentage of maximal HR (%HRmax), time spent in different HR zones, and estimated core temperature (ECTemp) were calculated. The effect of increasing rest across two harvests was evaluated for BCC and SC. RESULTS A total of 162 workers participated in this study [52 BCC (all male), 71 SC (13 female) and 39 DIRW (16 female)]. Average %HRmax across a work shift was similar between BCC and SC (BCC: 58%, SC: 59%), but lower in DIRW (51%). BCC and SC spent similar proportions of work shifts at hard/very hard intensities (BCC: 13%, SC: 15%), versus DIRW who worked mostly at light (46%) or light-moderate (39%) intensities. SC maximum ECTemp reached 38.2°C, BCC 38.1°C; while DIRW only reached 37.7°C. Females performed at a higher %HRmax than males across work shifts (SC 64% versus 58%; DIRW 55% versus 49%). An additional rest period was associated with a lower average %HRmax across a work shift in BCC. CONCLUSION In this setting, BCC and SC both undertake very physiologically demanding work. Females maintained a higher workload than male co-workers. Regulated rest periods each hour, with water and shade access, appears to reduce physiological workload/strain.
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Affiliation(s)
- Rebekah A I Lucas
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom.
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Abstract
The most common non-pharmacological intervention for both peripheral and cerebral vascular health is regular physical activity (e.g., exercise training), which improves function across a range of exercise intensities and modalities. Numerous non-exercising approaches have also been suggested to improved vascular function, including repeated ischemic preconditioning (IPC); heat therapy such as hot water bathing and sauna; and pneumatic compression. Chronic adaptive responses have been observed across a number of these approaches, yet the precise mechanisms that underlie these effects in humans are not fully understood. Acute increases in blood flow and circulating signalling factors that induce responses in endothelial function are likely to be key moderators driving these adaptations. While the impact on circulating factors and environmental mechanisms for adaptation may vary between approaches, in essence, they all centre around acutely elevating blood flow throughout the circulation and stimulating improved endothelium-dependent vascular function and ultimately vascular health. Here, we review our current understanding of the mechanisms driving endothelial adaptation to repeated exposure to elevated blood flow, and the interplay between this response and changes in circulating factors. In addition, we will consider the limitations in our current knowledge base and how these may be best addressed through the selection of more physiologically relevant experimental models and research. Ultimately, improving our understanding of the unique impact that non-pharmacological interventions have on the vasculature will allow us to develop superior strategies to tackle declining vascular function across the lifespan, prevent avoidable vascular-related disease, and alleviate dependency on drug-based interventions.
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Affiliation(s)
- Samuel R C Weaver
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK.
- Centre for Human Brain Health, University of Birmingham, Birmingham, UK.
| | - Catarina Rendeiro
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK
- Centre for Human Brain Health, University of Birmingham, Birmingham, UK
| | - Rebekah A I Lucas
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK
| | - N Timothy Cable
- Institute of Sport, Manchester Metropolitan University, Manchester, UK
| | - Tom E Nightingale
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK
| | - Helen M McGettrick
- Institute of Inflammation and Ageing, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
| | - Samuel J E Lucas
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK
- Centre for Human Brain Health, University of Birmingham, Birmingham, UK
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Weaver SRC, Rendeiro C, Lucas RAI, Cable NT, Nightingale TE, McGettrick HM, Lucas SJE. Non-pharmacological interventions for vascular health and the role of the endothelium. Eur J Appl Physiol 2022; 122:2493-2514. [PMID: 36149520 PMCID: PMC9613570 DOI: 10.1007/s00421-022-05041-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2022] [Accepted: 09/05/2022] [Indexed: 12/11/2022]
Abstract
The most common non-pharmacological intervention for both peripheral and cerebral vascular health is regular physical activity (e.g., exercise training), which improves function across a range of exercise intensities and modalities. Numerous non-exercising approaches have also been suggested to improved vascular function, including repeated ischemic preconditioning (IPC); heat therapy such as hot water bathing and sauna; and pneumatic compression. Chronic adaptive responses have been observed across a number of these approaches, yet the precise mechanisms that underlie these effects in humans are not fully understood. Acute increases in blood flow and circulating signalling factors that induce responses in endothelial function are likely to be key moderators driving these adaptations. While the impact on circulating factors and environmental mechanisms for adaptation may vary between approaches, in essence, they all centre around acutely elevating blood flow throughout the circulation and stimulating improved endothelium-dependent vascular function and ultimately vascular health. Here, we review our current understanding of the mechanisms driving endothelial adaptation to repeated exposure to elevated blood flow, and the interplay between this response and changes in circulating factors. In addition, we will consider the limitations in our current knowledge base and how these may be best addressed through the selection of more physiologically relevant experimental models and research. Ultimately, improving our understanding of the unique impact that non-pharmacological interventions have on the vasculature will allow us to develop superior strategies to tackle declining vascular function across the lifespan, prevent avoidable vascular-related disease, and alleviate dependency on drug-based interventions.
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Affiliation(s)
- Samuel R C Weaver
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK.
- Centre for Human Brain Health, University of Birmingham, Birmingham, UK.
| | - Catarina Rendeiro
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK
- Centre for Human Brain Health, University of Birmingham, Birmingham, UK
| | - Rebekah A I Lucas
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK
| | - N Timothy Cable
- Institute of Sport, Manchester Metropolitan University, Manchester, UK
| | - Tom E Nightingale
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK
| | - Helen M McGettrick
- Institute of Inflammation and Ageing, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
| | - Samuel J E Lucas
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK
- Centre for Human Brain Health, University of Birmingham, Birmingham, UK
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Alali MH, Lucas RAI, Junejo RT, Fisher JP. Impact of acute dynamic exercise and arterial shear rate modification on radial artery low-flow mediated constriction in young men. Eur J Appl Physiol 2022; 122:1885-1895. [PMID: 35551453 PMCID: PMC9287252 DOI: 10.1007/s00421-022-04963-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2021] [Accepted: 04/25/2022] [Indexed: 11/30/2022]
Abstract
Purpose Leg cycling exercise acutely augments radial artery low-flow mediated constriction (L-FMC). Herein, we sought to determine whether this is associated with exercise-induced changes in arterial shear rate (SR). Methods Ten healthy and recreationally active young men (23 ± 2 years) participated in 30 min of incremental leg cycling exercise (50, 100, 150 Watts). Trials were repeated with (Exercise + WC) and without (Exercise) the use of a wrist cuff (75 mmHg) placed distal to the radial artery to increase local retrograde SR while reducing mean and anterograde SR. Radial artery characteristics were measured throughout the trial, and L-FMC and flow mediated dilatation (FMD) were assessed before and acutely (~ 10 min) after leg cycling. Results Exercise increased radial artery mean and anterograde SR, along with radial artery diameter, velocity, blood flow and conductance (P < 0.05). Exercise + WC attenuated the exercise-induced increase in mean and anterograde SR (P > 0.05) but also increased retrograde SR (P < 0.05). In addition, increases in radial artery blood flow and diameter were reduced during Exercise + WC (Exercise + WC vs. Exercise, P < 0.05). After Exercise, L-FMC was augmented (− 4.4 ± 1.4 vs. − 13.1 ± 1.6%, P < 0.05), compared to no change in L-FMC after Exercise + WC (− 5.2 ± 2.0 vs. − 3.0 ± 1.6%, P > 0.05). In contrast, no change in FMD was observed in either Exercise or Exercise + WC trials (P > 0.05). Conclusions These findings indicate that increases in L-FMC following exercise are abolished by the prevention of increases radial artery diameter, mean and anterograde SR, and by elevation of retrograde SR, during exercise in young men.
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Affiliation(s)
- Mohammad H Alali
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Rebekah A I Lucas
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Rehan T Junejo
- Department of Life Sciences, Faculty of Science and Engineering, Manchester Metropolitan University, Manchester, United Kingdom
| | - James P Fisher
- Department of Physiology, Faculty of Medical and Health Sciences, Manaaki Manawa-The Centre for Heart Research, University of Auckland, 85 Park Road, Grafton, Auckland, 1142, New Zealand.
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Glaser J, Wegman DH, Arias-Monge E, Pacheco-Zenteno F, Prince H, Chavarria D, Martinez-Cuadra WJ, Jakobsson K, Hansson E, Lucas RAI, Weiss I, Wesseling C. Workplace Intervention for Heat Stress: Essential Elements of Design, Implementation, and Assessment. Int J Environ Res Public Health 2022; 19:ijerph19073779. [PMID: 35409463 PMCID: PMC8998134 DOI: 10.3390/ijerph19073779] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 02/24/2022] [Accepted: 03/14/2022] [Indexed: 11/16/2022]
Abstract
Heat stress is associated with numerous health effects that potentially harm workers, especially in a warming world. This investigation occurred in a setting where laborers are confronted with occupational heat stress from physically demanding work in high environmental temperatures. Collaboration with a major Nicaraguan sugarcane producer offered the opportunity to study interventions to prevent occupational heat-stress-related kidney disease. Two aims for this study of a rest-shade-water intervention program were: (1) describe the evolving intervention, summarize findings that motivated proposed improvements, assess impact of those improvements, and identify challenges to successful implementation and (2) extract primary lessons learned about intervention research that have both general relevance to investigations of work-related disease prevention and specific relevance to this setting. The learning curve for the various stakeholders as well as the barriers to success demonstrate that effectiveness of an intervention cannot be adequately assessed without considerations of implementation. Designing, effectively implementing, and assessing both health impacts and implementation quality is a resource-intensive endeavor requiring a transdisciplinary approach. Both general and specific lessons learned are presented for decisions on study design and study elements, implementation assessment, and management engagement in understanding how productivity and health can be successfully balanced and for building effective communication between investigators and all levels of management.
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Affiliation(s)
- Jason Glaser
- La Isla Network, 2219 California Ave NW, #52, Washington, DC 20008, USA; (E.A.-M.); (W.J.M.-C.); (K.J.); (E.H.); (R.A.I.L.); (I.W.); (C.W.)
- Correspondence: (J.G.); (D.H.W.); Tel.: +1-(347)-585-7465 (J.G.); +1-(617)-921-1506 (D.H.W.)
| | - David H. Wegman
- La Isla Network, 2219 California Ave NW, #52, Washington, DC 20008, USA; (E.A.-M.); (W.J.M.-C.); (K.J.); (E.H.); (R.A.I.L.); (I.W.); (C.W.)
- University of Massachusetts Lowell, Lowell, MA 01854, USA
- Correspondence: (J.G.); (D.H.W.); Tel.: +1-(347)-585-7465 (J.G.); +1-(617)-921-1506 (D.H.W.)
| | - Esteban Arias-Monge
- La Isla Network, 2219 California Ave NW, #52, Washington, DC 20008, USA; (E.A.-M.); (W.J.M.-C.); (K.J.); (E.H.); (R.A.I.L.); (I.W.); (C.W.)
- Unidad de Gestión Ambiental y Seguridad Laboral, Instituto Tecnológico de Costa Rica, 15th Street, 14th Avenue, Cartago 159-7050, Costa Rica
| | - Felipe Pacheco-Zenteno
- School of Public Health and Community Medicine, Sahlgrenska Academy, University of Gothenburg, 405 30 Göteborg, Sweden;
| | - Heath Prince
- Ray Marshall Center, LBJ School of Public Affairs, University of Texas at Austin, 3001 Lake Austin Blvd., Ste. 3.200, Austin, TX 78703, USA;
| | - Denis Chavarria
- Occupational Health, Ingenio San Antonio, Chinandega 26100, Nicaragua;
| | - William Jose Martinez-Cuadra
- La Isla Network, 2219 California Ave NW, #52, Washington, DC 20008, USA; (E.A.-M.); (W.J.M.-C.); (K.J.); (E.H.); (R.A.I.L.); (I.W.); (C.W.)
| | - Kristina Jakobsson
- La Isla Network, 2219 California Ave NW, #52, Washington, DC 20008, USA; (E.A.-M.); (W.J.M.-C.); (K.J.); (E.H.); (R.A.I.L.); (I.W.); (C.W.)
- School of Public Health and Community Medicine, Sahlgrenska Academy, University of Gothenburg, 405 30 Göteborg, Sweden;
- Occupational and Environmental Medicine, Sahlgrenska University Hospital, 405 30 Göteborg, Sweden
| | - Erik Hansson
- La Isla Network, 2219 California Ave NW, #52, Washington, DC 20008, USA; (E.A.-M.); (W.J.M.-C.); (K.J.); (E.H.); (R.A.I.L.); (I.W.); (C.W.)
- School of Public Health and Community Medicine, Sahlgrenska Academy, University of Gothenburg, 405 30 Göteborg, Sweden;
| | - Rebekah A. I. Lucas
- La Isla Network, 2219 California Ave NW, #52, Washington, DC 20008, USA; (E.A.-M.); (W.J.M.-C.); (K.J.); (E.H.); (R.A.I.L.); (I.W.); (C.W.)
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Ilana Weiss
- La Isla Network, 2219 California Ave NW, #52, Washington, DC 20008, USA; (E.A.-M.); (W.J.M.-C.); (K.J.); (E.H.); (R.A.I.L.); (I.W.); (C.W.)
| | - Catharina Wesseling
- La Isla Network, 2219 California Ave NW, #52, Washington, DC 20008, USA; (E.A.-M.); (W.J.M.-C.); (K.J.); (E.H.); (R.A.I.L.); (I.W.); (C.W.)
- Unit of Occupational Medicine, Institute of Environmental Medicine, Karolinska Institutet, Solnavägen 4, 113 65 Stockholm, Sweden
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10
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Kirby NV, Lucas SJE, Cable TG, Armstrong OJ, Weaver SR, Lucas RAI. Sex differences in adaptation to intermittent post-exercise sauna bathing in trained middle-distance runners. Sports Med Open 2021; 7:51. [PMID: 34297227 PMCID: PMC8302716 DOI: 10.1186/s40798-021-00342-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Accepted: 06/30/2021] [Indexed: 11/16/2022]
Abstract
Background The purpose of this study was to investigate the effect of sex on the efficacy of intermittent post-exercise sauna bathing to induce heat acclimation and improve markers of temperate exercise performance in trained athletes. Methods Twenty-six trained runners (16 female; mean ± SD, age 19 ± 1 years, V̇O2max F: 52.6 ± 6.9 mL⋅kg−1⋅min−1, M: 64.6 ± 2.4 mL⋅kg−1⋅min−1) performed a running heat tolerance test (30 min, 9 km⋅h−1/2% gradient, 40 °C/40%RH; HTT) and temperate (18 °C) exercise tests (maximal aerobic capacity [V̇O2max] and lactate profile) pre and post 3 weeks of normal exercise training plus 29 ± 1 min post-exercise sauna bathing (101–108 °C) 3 ± 1 times per week. Results Females and males exhibited similar reductions (interactions p > 0.05) in peak rectal temperature (− 0.3 °C; p < 0.001), skin temperature (− 0.9 °C; p < 0.001) and heart rate (− 9 beats·min−1; p = 0.001) during the HTT at post- vs pre-intervention. Only females exhibited an increase in active sweat glands on the forearm (measured via modified iodine technique; F: + 57%, p < 0.001; M: + 1%, p = 0.47). Conversely, only males increased forearm blood flow (measured via venous occlusion plethysmography; F: + 31%, p = 0.61; M: + 123%; p < 0.001). Females and males showed similar (interactions p > 0.05) improvements in V̇O2max (+ 5%; p = 0.02) and running speed at 4 mmol·L−1 blood lactate concentration (+ 0.4 km·h−1; p = 0.001). Conclusions Three weeks of post-exercise sauna bathing effectively induces heat acclimation in females and males, though possibly amid different thermoeffector adaptations. Post-exercise sauna bathing is also an effective ergogenic aid for both sexes. Supplementary Information The online version contains supplementary material available at 10.1186/s40798-021-00342-6.
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Affiliation(s)
- Nathalie V Kirby
- School of Sport Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK. .,Human and Environmental Physiology Research Unit, University of Ottawa, Ottawa, K1N 6N5, Canada.
| | - Samuel J E Lucas
- School of Sport Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK
| | - Thomas G Cable
- School of Sport Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK.,Loughborough University, Loughborough, UK
| | | | - Samuel R Weaver
- School of Sport Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK
| | - Rebekah A I Lucas
- School of Sport Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK
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11
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Chapman CL, Hess HW, Lucas RAI, Glaser J, Saran R, Bragg-Gresham J, Wegman DH, Hansson E, Minson CT, Schlader ZJ. Occupational heat exposure and the risk of chronic kidney disease of nontraditional origin in the United States. Am J Physiol Regul Integr Comp Physiol 2021; 321:R141-R151. [PMID: 34161738 DOI: 10.1152/ajpregu.00103.2021] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Occupational heat exposure is linked to the development of kidney injury and disease in individuals who frequently perform physically demanding work in the heat. For instance, in Central America, an epidemic of chronic kidney disease of nontraditional origin (CKDnt) is occurring among manual laborers, whereas potentially related epidemics have emerged in India and Sri Lanka. There is growing concern that workers in the United States suffer with CKDnt, but reports are limited. One of the leading hypotheses is that repetitive kidney injury caused by physical work in the heat can progress to CKDnt. Whether heat stress is the primary causal agent or accelerates existing underlying pathology remains contested. However, the current evidence supports that heat stress induces tubular kidney injury, which is worsened by higher core temperatures, dehydration, longer work durations, muscle damaging exercise, and consumption of beverages containing high levels of fructose. The purpose of this narrative review is to identify occupations that may place US workers at greater risk of kidney injury and CKDnt. Specifically, we reviewed the scientific literature to characterize the demographics, environmental conditions, physiological strain (i.e., core temperature increase, dehydration, heart rate), and work durations in sectors typically experiencing occupational heat exposure, including farming, wildland firefighting, landscaping, and utilities. Overall, the surprisingly limited available evidence characterizing occupational heat exposure in US workers supports the need for future investigations to understand this risk of CKDnt.
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Affiliation(s)
| | - Hayden W Hess
- Department of Kinesiology, School of Public Health, Indiana University, Bloomington, Indiana
| | - Rebekah A I Lucas
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Jason Glaser
- La Isla Network, Washington, D.C.,Responsible Business Center at Birkbeck, University of London, London, United Kingdom
| | - Rajiv Saran
- Division of Nephrology and the Kidney Epidemiology and Cost Center, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan.,Department of Epidemiology, School of Public Health, University of Michigan, Ann Arbor, Michigan
| | - Jennifer Bragg-Gresham
- Division of Nephrology and the Kidney Epidemiology and Cost Center, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan
| | - David H Wegman
- Department of Epidemiology, University of Massachusetts Lowell, Lowell, Massachusetts
| | - Erik Hansson
- La Isla Network, Washington, D.C.,School of Public Health and Community Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | | | - Zachary J Schlader
- Department of Kinesiology, School of Public Health, Indiana University, Bloomington, Indiana
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12
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Skinner BD, Davies RJ, Weaver SR, Cable NT, Lucas SJE, Lucas RAI. A Systematic Review and Meta-Analysis Examining Whether Changing Ovarian Sex Steroid Hormone Levels Influence Cerebrovascular Function. Front Physiol 2021; 12:687591. [PMID: 34220552 PMCID: PMC8248489 DOI: 10.3389/fphys.2021.687591] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Accepted: 05/21/2021] [Indexed: 01/14/2023] Open
Abstract
Sex differences in cerebrovascular disease rates indicate a possible role for ovarian sex steroid hormones in cerebrovascular function. To synthesise and identify knowledge gaps, a systematic review and meta-analysis was conducted to assess how ovarian sex steroid hormone changes across the lifespan affect cerebrovascular function in women. Three databases (EMBASE, MEDLINE and Web of Science) were systematically searched for studies on adult cerebrovascular function and ovarian sex steroid hormones. Forty-five studies met pre-defined inclusion criteria. Studied hormone groups included hormone replacement therapy (HRT; n = 17), pregnancy (n = 12), menstrual cycle (n = 7), menopause (n = 5), oral contraception (n = 2), and ovarian hyperstimulation (n = 2). Outcome measures included pulsatility index (PI), cerebral blood flow/velocity (CBF), resistance index (RI), cerebral autoregulation, and cerebrovascular reactivity. Meta-analysis was carried out on HRT studies. PI significantly decreased [−0.05, 95% CI: (−0.10, −0.01); p = 0.01] in post-menopausal women undergoing HRT compared to post-menopausal women who were not, though there was considerable heterogeneity (I2 = 96.8%). No effects of HRT were seen in CBF (p = 0.24) or RI (p = 0.77). This review indicates that HRT improves PI in post-menopausal women. However, there remains insufficient evidence to determine how changing ovarian sex steroid hormone levels affects cerebrovascular function in women during other hormonal phases (e.g., pregnancy, oral contraception).
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Affiliation(s)
- Bethany D Skinner
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom.,Centre for Human Brain Health, University of Birmingham, Birmingham, United Kingdom
| | - Rebecca J Davies
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Samuel R Weaver
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom.,Centre for Human Brain Health, University of Birmingham, Birmingham, United Kingdom
| | - N Tim Cable
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Samuel J E Lucas
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom.,Centre for Human Brain Health, University of Birmingham, Birmingham, United Kingdom
| | - Rebekah A I Lucas
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
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13
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Weaver SR, Skinner BD, Furlong R, Lucas RAI, Cable NT, Rendeiro C, McGettrick HM, Lucas SJE. Corrigendum: Cerebral Hemodynamic and Neurotrophic Factor Responses Are Dependent on the Type of Exercise. Front Physiol 2021; 12:659873. [PMID: 33716797 PMCID: PMC7945589 DOI: 10.3389/fphys.2021.659873] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2021] [Accepted: 02/08/2021] [Indexed: 11/13/2022] Open
Affiliation(s)
- Samuel R Weaver
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom.,Centre for Human Brain Health, University of Birmingham, Birmingham, United Kingdom
| | - Bethany D Skinner
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Rhodri Furlong
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Rebekah A I Lucas
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - N Timothy Cable
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Catarina Rendeiro
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom.,Centre for Human Brain Health, University of Birmingham, Birmingham, United Kingdom
| | - Helen M McGettrick
- College of Medical and Dental Sciences, Institute of Inflammation and Ageing, University of Birmingham, Birmingham, United Kingdom
| | - Samuel J E Lucas
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom.,Centre for Human Brain Health, University of Birmingham, Birmingham, United Kingdom
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14
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Weaver SR, Skinner BD, Furlong R, Lucas RAI, Cable NT, Rendeiro C, McGettrick HM, Lucas SJE. Cerebral Hemodynamic and Neurotrophic Factor Responses Are Dependent on the Type of Exercise. Front Physiol 2021; 11:609935. [PMID: 33551835 PMCID: PMC7859714 DOI: 10.3389/fphys.2020.609935] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2020] [Accepted: 12/07/2020] [Indexed: 12/25/2022] Open
Abstract
This study examined acute cerebral hemodynamic and circulating neurotrophic factor responses to moderate intensity continuous exercise (MICT), guideline-based high intensity interval exercise (HIIT), and sprint interval exercise (SIT). We hypothesized that the pattern of middle cerebral artery velocity (MCAv) response would differ between interval and continuous exercise, with SIT inducing the smallest increase from rest, while increases in neurotrophic factors would be intensity-dependent. In a randomized crossover design, 24 healthy adults (nine females) performed three exercise protocols: (i) MICT (30 min), (ii) HIIT (4 × 4 min at 85% HRmax), and (iii) SIT (4 × 30 s supramaximal). MCAv significantly increased from rest across MICT (Δ13.1 ± 8.5 cm⋅s–1, p < 0.001) and all bouts of HIIT (Δ15.2 ± 9.8 cm⋅s–1, p < 0.001), but only for the initial bout of SIT (Δ17.3 ± 11.6 cm⋅s–1, p < 0.001). Immediately following each interval bout, MCAv increased (i.e., rebounded) for the SIT (9–14% above rest, p ≤ 0.04), but not HIIT protocol. SIT alone induced significant elevations from rest to end-exercise in vascular endothelial growth factor (VEGF; Δ28 ± 36%, p = 0.017) and brain-derived neurotrophic factor (BDNF, Δ149% ± 162%, p < 0.001) and there were greater increases in lactate than in either other protocol (>5-fold greater in SIT, p < 0.001), alongside a small significant reduction at the end of active recovery in insulin-like growth factor 1 (IGF-1, Δ22 ± 21%, p = 0.002). In conclusion, while the nature of the response may differ, both guideline-based and sprint-based interval exercise have the potential to induce significant changes in factors linked to improved cerebrovascular and brain health.
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Affiliation(s)
- Samuel R Weaver
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom.,Centre for Human Brain Health, University of Birmingham, Birmingham, United Kingdom
| | - Bethany D Skinner
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Rhodri Furlong
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Rebekah A I Lucas
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - N Timothy Cable
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Catarina Rendeiro
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom.,Centre for Human Brain Health, University of Birmingham, Birmingham, United Kingdom
| | - Helen M McGettrick
- College of Medical and Dental Sciences, Institute of Inflammation and Ageing, University of Birmingham, Birmingham, United Kingdom
| | - Samuel J E Lucas
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom.,Centre for Human Brain Health, University of Birmingham, Birmingham, United Kingdom
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15
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Alali MH, Vianna LC, Lucas RAI, Junejo RT, Fisher JP. Impact of whole body passive heat stress and arterial shear rate modification on radial artery function in young men. J Appl Physiol (1985) 2020; 129:1373-1382. [PMID: 33031019 DOI: 10.1152/japplphysiol.00296.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We sought to determine how whole body heating acutely influences radial artery function, characterized using flow-mediated dilation (FMD) and low-flow-mediated constriction (L-FMC), and the mechanistic role of shear rate modification on radial artery functional characteristics during heating. Eleven young healthy men underwent whole body heating (water-perfused suit) sufficient to raise the core temperature by +1°C. Trials were repeated with (heat + WC) and without (heat) the application of a wrist cuff located distal to the radial artery examined, known to prevent increases in mean and anterograde shear rates but increase retrograde shear rate. Radial artery characteristics were assessed throughout each trial, with FMD and L-FMC assessed before and upon reaching the target core temperature. Heat markedly increased radial artery mean and anterograde shear rates, along with radial artery diameter and blood flow (P < 0.05). Heat + WC abolished the heat-induced increase in mean and anterograde shear rates (P > 0.05) but markedly increased retrograde shear rate (P < 0.05). Concomitantly, increases in radial artery diameter and blood flow were decreased (heat + WC vs. heat, P < 0.05). Heat attenuated FMD (8.6 ± 1.2% vs. 2.2 ± 1.4%, P < 0.05), whereas no change in FMD was observed in heat + WC (7.8 ± 1.2% vs. 10.8 ± 1.2%, P > 0.05). In contrast, L-FMC was not different in either trial (P > 0.05). In summary, acute whole body heating markedly elevates radial artery shear rate, diameter, and blood flow and diminishes FMD. However, marked radial artery vasodilation and diminished FMD are absent when these shear rate changes are prevented. Shear rate modifications underpin the radial artery response to acute whole body heat stress, but further endothelium-dependent vasodilation (FMD) is attenuated likely as the vasodilatory range limit is approached.NEW & NOTEWORTHY We observed that acute whole body heating elevates radial artery shear rate, diameter, and blood flow. This results in a diminished flow-meditated dilatation (FMD) but does not change low-flow-mediated constriction (L-FMC). Preventing shear rate changes during whole body heating reduces radial artery vasodilation and reverses FMD reductions but has no effect on L-FMC. These findings indicate that shear rate changes underpin conduit artery responses to acute whole body heat stress, but further endothelium-dependent flow-mediated vasodilation is attenuated as the vasodilatory range limit is approached.
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Affiliation(s)
- Mohammad H Alali
- School of Sport, Exercise & Rehabilitation Sciences, College of Life & Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Lauro C Vianna
- NeuroV̇ASQ̇ - Integrative Physiology Laboratory, Faculty of Physical Education, University of Brasília, Distrito Federal, Brazil
| | - Rebekah A I Lucas
- School of Sport, Exercise & Rehabilitation Sciences, College of Life & Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Rehan T Junejo
- Department of Life Sciences, Manchester Metropolitan University, Manchester, United Kingdom.,Liverpool Centre for Cardiovascular Science, University of Liverpool, Liverpool, United Kingdom
| | - James P Fisher
- Faculty of Medical & Health Sciences, Department of Physiology, University of Auckland, Auckland, New Zealand
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16
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Kirby NV, Lucas SJE, Armstrong OJ, Weaver SR, Lucas RAI. Intermittent post-exercise sauna bathing improves markers of exercise capacity in hot and temperate conditions in trained middle-distance runners. Eur J Appl Physiol 2020; 121:621-635. [PMID: 33211153 PMCID: PMC7862510 DOI: 10.1007/s00421-020-04541-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Accepted: 10/24/2020] [Indexed: 10/27/2022]
Abstract
PURPOSE This study investigated whether intermittent post-exercise sauna bathing across three-weeks endurance training improves exercise heat tolerance and exercise performance markers in temperate conditions, compared to endurance training alone. The subsidiary aim was to determine whether exercise-heat tolerance would further improve following 7-Weeks post-exercise sauna bathing. METHODS Twenty middle-distance runners (13 female; mean ± SD, age 20 ± 2 years, [Formula: see text]O2max 56.1 ± 8.7 ml kg-1 min-1) performed a running heat tolerance test (30-min, 9 km h-1/2% gradient, 40 °C/40%RH; HTT) and temperate (18 °C) exercise tests (maximal aerobic capacity [[Formula: see text]O2max], speed at 4 mmol L-1 blood lactate concentration ([La-]) before (Pre) and following three-weeks (3-Weeks) normal training (CON; n = 8) or normal training with 28 ± 2 min post-exercise sauna bathing (101-108 °C, 5-10%RH) 3 ± 1 times per week (SAUNA; n = 12). Changes from Pre to 3-Weeks were compared between-groups using an analysis of co-variance. Six SAUNA participants continued the intervention for 7 weeks, completing an additional HTT (7-Weeks; data compared using a one-way repeated-measures analysis of variance). RESULTS During the HTT, SAUNA reduced peak rectal temperature (Trec; - 0.2 °C), skin temperature (- 0.8 °C), and heart rate (- 11 beats min-1) more than CON at 3-Weeks compared to Pre (all p < 0.05). SAUNA also improved [Formula: see text]O2max (+ 0.27 L-1 min-1; p = 0.02) and speed at 4 mmol L-1 [La-] (+ 0.6 km h-1; p = 0.01) more than CON at 3-Weeks compared to Pre. Only peak Trec (- 0.1 °C; p = 0.03 decreased further from 3-Weeks to 7-Weeks in SAUNA (other physiological variables p > 0.05). CONCLUSIONS Three-weeks post-exercise sauna bathing is an effective and pragmatic method of heat acclimation, and an effective ergogenic aid. Extending the intervention to seven weeks only marginally improved Trec.
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17
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Furlong RJ, Weaver SR, Sutherland R, Burley CV, Imi GM, Lucas RAI, Lucas SJE. Exercise-induced elevations in cerebral blood velocity are greater in running compared to cycling at higher intensities. Physiol Rep 2020; 8:e14539. [PMID: 32786068 PMCID: PMC7422808 DOI: 10.14814/phy2.14539] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Revised: 07/20/2020] [Accepted: 07/20/2020] [Indexed: 12/14/2022] Open
Abstract
The optimal exercise intensity and modality for maximizing cerebral blood flow (CBF) and hence potential exposure to positive, hemodynamically derived cerebral adaptations is yet to be fully determined. This study compared CBF velocity responses between running and cycling across a range of exercise intensities. Twenty-six participants (12 females; age: 26 ± 8 years) completed four exercise sessions; two mode-specific maximal oxygen consumption (VO2max ) tests, followed by (order randomized) two incremental exercise protocols (3-min stages at 35%, 50%, 65%, 80%, 95% VO2max ). Continuous measures of middle cerebral artery velocity (MCAv), oxygen consumption, end-tidal CO2 (PET CO2 ), and heart rate were obtained. Modality-specific MCAv changes were observed for the whole group (interaction effect: p = .01). Exercise-induced increases in MCAvmean during cycling followed an inverted-U pattern, peaking at 65% VO2max (Δ12 ± 7 cm/s from rest), whereas MCAvmean during running increased linearly up to 95% VO2max (change from rest: Δ12 ± 13 vs. Δ7 ± 8 cm/s for running vs. cycling at 95% VO2max ; p = .01). In contrast, both modalities had an inverted-U pattern for PET CO2 changes, although peaked at different intensities (running: 50% VO2max , Δ6 ± 2 mmHg; cycling: 65% VO2max , Δ7 ± 2 mmHg; interaction effect: p = .01). Further subgroup analysis revealed that the running-specific linear MCAvmean response was fitness dependent (Fitness*modality*intensity interaction effect: p = .04). Above 65% VO2max , fitter participants (n = 16; male > 45 mL/min/kg and female > 40 mL/min/kg) increased MCAvmean up to 95% VO2max , whereas in unfit participants (n = 7, male < mL/min/kg and female < 35 mL/min/kg) MCAvmean returned toward resting values. Findings demonstrate that modality- and fitness-specific profiles for MCAvmean are seen at exercise intensities exceeding 65% VO2max .
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Affiliation(s)
- Rhodri J. Furlong
- School of Sport, Exercise and Rehabilitation SciencesCollege of Life and Environmental SciencesUniversity of BirminghamBirminghamUK
| | - Samuel R. Weaver
- School of Sport, Exercise and Rehabilitation SciencesCollege of Life and Environmental SciencesUniversity of BirminghamBirminghamUK
- Centre for Human Brain HealthUniversity of BirminghamBirminghamUK
| | - Rory Sutherland
- School of Sport, Exercise and Rehabilitation SciencesCollege of Life and Environmental SciencesUniversity of BirminghamBirminghamUK
| | - Claire V. Burley
- School of Sport, Exercise and Rehabilitation SciencesCollege of Life and Environmental SciencesUniversity of BirminghamBirminghamUK
- Centre for Human Brain HealthUniversity of BirminghamBirminghamUK
- Dementia Centre for Research CollaborationSchool of PsychiatryUniversity of New South WalesSydneyAustralia
| | - Gabriella M. Imi
- School of Sport, Exercise and Rehabilitation SciencesCollege of Life and Environmental SciencesUniversity of BirminghamBirminghamUK
| | - Rebekah A. I. Lucas
- School of Sport, Exercise and Rehabilitation SciencesCollege of Life and Environmental SciencesUniversity of BirminghamBirminghamUK
| | - Samuel J. E. Lucas
- School of Sport, Exercise and Rehabilitation SciencesCollege of Life and Environmental SciencesUniversity of BirminghamBirminghamUK
- Centre for Human Brain HealthUniversity of BirminghamBirminghamUK
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18
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Hansson E, Glaser J, Jakobsson K, Weiss I, Wesseling C, Lucas RAI, Wei JLK, Ekström U, Wijkström J, Bodin T, Johnson RJ, Wegman DH. Pathophysiological Mechanisms by which Heat Stress Potentially Induces Kidney Inflammation and Chronic Kidney Disease in Sugarcane Workers. Nutrients 2020; 12:E1639. [PMID: 32498242 PMCID: PMC7352879 DOI: 10.3390/nu12061639] [Citation(s) in RCA: 45] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2020] [Revised: 05/22/2020] [Accepted: 05/25/2020] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND Chronic kidney disease of non-traditional origin (CKDnt) is common among Mesoamerican sugarcane workers. Recurrent heat stress and dehydration is a leading hypothesis. Evidence indicate a key role of inflammation. METHODS Starting in sports and heat pathophysiology literature, we develop a theoretical framework of how strenuous work in heat could induce kidney inflammation. We describe the release of pro-inflammatory substances from a leaky gut and/or injured muscle, alone or in combination with tubular fructose and uric acid, aggravation by reduced renal blood flow and increased tubular metabolic demands. Then, we analyze longitudinal data from >800 sugarcane cutters followed across harvest and review the CKDnt literature to assess empirical support of the theoretical framework. RESULTS Inflammation (CRP elevation and fever) and hyperuricemia was tightly linked to kidney injury. Rehydrating with sugary liquids and NSAID intake increased the risk of kidney injury, whereas electrolyte solution consumption was protective. Hypokalemia and hypomagnesemia were associated with kidney injury. DISCUSSION Heat stress, muscle injury, reduced renal blood flow and fructose metabolism may induce kidney inflammation, the successful resolution of which may be impaired by daily repeating pro-inflammatory triggers. We outline further descriptive, experimental and intervention studies addressing the factors identified in this study.
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Affiliation(s)
- Erik Hansson
- School of Public Health and Community Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Box 414, 405 30 Gothenburg, Sweden;
- La Isla Network, 1441 L Street NW, Washington, DC 20005, USA; (J.G.); (I.W.); (C.W.); (R.A.I.L.); (U.E.); (D.H.W.)
| | - Jason Glaser
- La Isla Network, 1441 L Street NW, Washington, DC 20005, USA; (J.G.); (I.W.); (C.W.); (R.A.I.L.); (U.E.); (D.H.W.)
- Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK
| | - Kristina Jakobsson
- School of Public Health and Community Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Box 414, 405 30 Gothenburg, Sweden;
- La Isla Network, 1441 L Street NW, Washington, DC 20005, USA; (J.G.); (I.W.); (C.W.); (R.A.I.L.); (U.E.); (D.H.W.)
- Occupational and Environmental Medicine, Sahlgrenska University Hospital, Box 414, 405 30 Gothenburg, Sweden
| | - Ilana Weiss
- La Isla Network, 1441 L Street NW, Washington, DC 20005, USA; (J.G.); (I.W.); (C.W.); (R.A.I.L.); (U.E.); (D.H.W.)
| | - Catarina Wesseling
- La Isla Network, 1441 L Street NW, Washington, DC 20005, USA; (J.G.); (I.W.); (C.W.); (R.A.I.L.); (U.E.); (D.H.W.)
- Institute of Environmental Medicine, Karolinska Institutet, Nobels väg 13, 171 65 Solna, Sweden;
| | - Rebekah A. I. Lucas
- La Isla Network, 1441 L Street NW, Washington, DC 20005, USA; (J.G.); (I.W.); (C.W.); (R.A.I.L.); (U.E.); (D.H.W.)
- School of Sport, Exercise & Rehabilitation Sciences, University of Birmingham, 142 Edgbaston Park Rd, Birmingham B15 2TT, UK
| | - Jason Lee Kai Wei
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, 2 Medical Drive, MD9, National University of Singapore, Singapore 117593, Singapore;
- Global Asia Institute, National University of Singapore, 10 Lower Kent Ridge Rd, Singapore 119076, Singapore
- N.1 Institute for Health, National University of Singapore, 28 Medical Dr, Singapore 117456, Singapore
| | - Ulf Ekström
- La Isla Network, 1441 L Street NW, Washington, DC 20005, USA; (J.G.); (I.W.); (C.W.); (R.A.I.L.); (U.E.); (D.H.W.)
- Department of Laboratory Medicine, Division of Clinical Chemistry and Pharmacology, Lund University, 221 85 Lund, Sweden
| | - Julia Wijkström
- Division of Renal Medicine, Department of Clinical Science Intervention and Technology, Karolinska Institutet, 141 86 Stockholm, Sweden;
| | - Theo Bodin
- Institute of Environmental Medicine, Karolinska Institutet, Nobels väg 13, 171 65 Solna, Sweden;
| | - Richard J. Johnson
- Division of Renal Diseases and Hypertension, School of Medicine, University of Colorado Denver, Aurora, CO 80045, USA;
| | - David H. Wegman
- La Isla Network, 1441 L Street NW, Washington, DC 20005, USA; (J.G.); (I.W.); (C.W.); (R.A.I.L.); (U.E.); (D.H.W.)
- Department of Work Environment, University of Massachusetts Lowell, Lowell, MA 01845, USA
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Burley CV, Lucas RAI, Whittaker AC, Mullinger K, Lucas SJE. The CO 2 stimulus duration and steady-state time point used for data extraction alters the cerebrovascular reactivity outcome measure. Exp Physiol 2020; 105:893-903. [PMID: 32083357 DOI: 10.1113/ep087883] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2019] [Accepted: 02/19/2020] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the central question of this study? Cerebrovascular reactivity (CVR) is a common functional test to assess brain health, and impaired CVR has been associated with all-cause cardiovascular mortality: does the duration of the CO2 stimulus and the time point used for data extraction alter the CVR outcome measure? What is the main finding and its importance? This study demonstrated CVR measures calculated from 1 and 2 min CO2 stimulus durations were significantly higher than CVR calculated from a 4 min CO2 stimulus. CVRs calculated from the first 2 min of the CO2 stimulus were significantly higher than CVR values calculated from the final minute if the duration was ≥4 min. This study highlights the need for consistent methodological approaches. ABSTRACT Cerebrovascular reactivity to carbon dioxide (CVR) is a common functional test to assess brain vascular health, though conflicting age and fitness effects have been reported. Studies have used different CO2 stimulus durations to induce CVR and extracted data from different time points for analysis. Therefore, this study examined whether these differences alter CVR and explain conflicting findings. Eighteen healthy volunteers (24 ± 5 years) inhaled CO2 for four stimulus durations (1, 2, 4 and 5 min) of 5% CO2 (in air) via the open-circuit Douglas bag method, in a randomized order. CVR data were derived from transcranial Doppler (TCD) measures of middle cerebral artery blood velocity (MCAv), with concurrent ventilatory sensitivity to the CO2 stimulus ( V ̇ E , C O 2 ). Repeated measures ANOVAs compared CVR and V ̇ E , C O 2 measures between stimulus durations and steady-state time points. An effect of stimulus duration was observed (P = 0.002, η² = 0.140), with 1 min (P = 0.010) and 2 min (P < 0.001) differing from 4 min, and 2 min differing from 5 min (P = 0.019) durations. V ̇ E , C O 2 sensitivity increased ∼3-fold from 1 min to 4 and 5 min durations (P < 0.001, η² = 0.485). CVRs calculated from different steady-state time points within each stimulus duration were different (P < 0.001, η² = 0.454), specifically for 4 min (P = 0.001) and 5 min (P < 0.001), but not 2 min stimulus durations (P = 0.273). These findings demonstrate that methodological differences alter the CVR measure.
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Affiliation(s)
- Claire V Burley
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK.,Centre for Human Brain Health, University of Birmingham, Birmingham, UK
| | - Rebekah A I Lucas
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK
| | - Anna C Whittaker
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK
| | - Karen Mullinger
- Centre for Human Brain Health, University of Birmingham, Birmingham, UK.,School of Psychology, University of Birmingham, Birmingham, UK.,School of Physics and Astronomy, University of Nottingham, Nottingham, UK
| | - Samuel J E Lucas
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK.,Centre for Human Brain Health, University of Birmingham, Birmingham, UK.,Department of Physiology, University of Otago, New Zealand
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20
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Abstract
OBJECTIVE Menopausal hot flushes negatively impact quality of life and may be a biomarker of cardiovascular and metabolic disease risk; therefore understanding the physiology of hot flushes is important. Current thinking is that a small elevation (∼0.03-0.05C) in core temperature surpasses a sweating threshold (that is reduced in the menopause), sweating is activated, and a hot flush ensues. Nevertheless, more recent studies examining thermoregulatory control question whether core temperature per se can explain the trigger for a hot flush. The primary aim of this study was to assess the contribution of increases in core temperature on the occurrence of menopausal hot flushes. METHODS For this purpose, 108 hot flushes were objectively assessed in a laboratory setting in 72 symptomatic postmenopausal women (aged 45.8 ± 5.1 years; body mass index 25.9 ± 4.5 kg/m) from five previously reported studies. Women rested, wearing a tube-lined suit (or trousers), which was perfused with 34C water. A subset then underwent mild heat stress (48°C water). Sweat rate, skin blood flow, blood pressure, heart rate, skin, and core temperature were measured continuously throughout. A hot flush was objectively identified during rest (spontaneous hot flush) or mild heating as an abrupt increase in sternal sweat rate. Further, a subset of symptomatic postmenopausal women (n = 22) underwent whole-body passive heating for 60 minutes to identify core temperature thresholds and sensitivities for sweat rate and cutaneous vasodilation, which were compared to a subset of premenopausal women (n = 18). Data were analyzed using t tests and/or general linear modeling, and are presented as mean (95% confidence interval). RESULTS In the 20 minutes before a spontaneous hot flush, core temperature increased by 0.03 ± 0.12C (P < 0.05), but only 51% of hot flushes were preceded by an increase in core temperature. During mild heating, 76% of hot flushes were preceded by an increase in core temperature. The temperature thresholds for sweating were similar, but the vasodilatory threshold was higher in postmenopausal compared with premenopausal women (37.1 ± 0.2 vs 36.8 ± 0.3°C; P = 0.06). CONCLUSION We provide new evidence that menopausal hot flushes are unlikely triggered by an increase in core temperature. These findings provide important information about the physiology of hot flushes that have implications for treatment and management options for menopausal hot flushes.
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Affiliation(s)
- Helen Jones
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, England
| | - Tom G Bailey
- Centre for Research on Exercise, Physical Activity and Health, School of Human Movement and Nutrition Sciences, The University of Queensland, Australia
| | - David A Barr
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, England
| | - Madeleine France
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, England
| | - Rebekah A I Lucas
- School of Sport, Exercise and Rehabilitative Sciences, University of Birmingham, Birmingham, UK
| | - Craig G Crandall
- Department of Internal Medicine, University of Texas Southwestern and Texas Health Presbyterian Hospital Dallas, TX
| | - David A Low
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, England
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21
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Kirby NV, Lucas SJE, Lucas RAI. Nine-, but Not Four-Days Heat Acclimation Improves Self-Paced Endurance Performance in Females. Front Physiol 2019; 10:539. [PMID: 31156449 PMCID: PMC6532023 DOI: 10.3389/fphys.2019.00539] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Accepted: 04/16/2019] [Indexed: 11/13/2022] Open
Abstract
Although emerging as a cost and time efficient way to prepare for competition in the heat, recent evidence indicates that "short-term" heat acclimation (<7 days) may not be sufficient for females to adapt to repeated heat stress. Furthermore, self-paced performance following either short-term, or longer (>7 days) heat acclimation has not been examined in a female cohort. Therefore, the aim of this study was to investigate self-paced endurance performance in hot conditions following 4- and 9-days of a high-intensity isothermic heat acclimation protocol in a female cohort. Eight female endurance athletes (mean ± SD, age 27 ± 5 years, mass 61 ± 5 kg, VO2peak 47 ± 6 ml⋅kg⋅min-1) performed 15-min self-paced cycling time trials in hot conditions (35°C, 30%RH) before (HTT1), and after 4-days (HTT2), and 9-days (HTT3) isothermic heat acclimation (HA, with power output manipulated to increase and maintain rectal temperature (T rec) at ∼38.5°C for 90-min cycling in 40°C, 30%RH) with permissive dehydration. There were no significant changes in distance cycled (p = 0.47), mean power output (p = 0.55) or cycling speed (p = 0.44) following 4-days HA (i.e., from HTT1 to HTT2). Distance cycled (+3.2%, p = 0.01; +1.8%, p = 0.04), mean power output (+8.1%, p = 0.01; +4.8%, p = 0.05) and cycling speed (+3.0%, p = 0.01; +1.6%, p = 0.05) were significantly greater in HTT3 than in HTT1 and HTT2, respectively. There was an increase in the number of active sweat glands per cm2 in HTT3 as compared to HTT1 (+32%; p = 0.02) and HTT2 (+22%; p < 0.01), whereas thermal sensation immediately before HTT3 decreased ("Slightly Warm," p = 0.03) compared to ratings taken before HTT1 ("Warm") in 35°C, 30%RH. Four-days HA was insufficient to improve performance in the heat in females as observed following 9-days HA.
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Affiliation(s)
- Nathalie V. Kirby
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom
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22
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Huang M, Brothers RM, Ganio MS, Lucas RAI, Cramer MN, Moralez G, Convertino VA, Crandall CG. Tolerance to a haemorrhagic challenge during heat stress is improved with inspiratory resistance breathing. Exp Physiol 2018; 103:1243-1250. [PMID: 29947436 PMCID: PMC6119106 DOI: 10.1113/ep087102] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2018] [Accepted: 06/22/2018] [Indexed: 02/06/2023]
Abstract
NEW FINDINGS What is the central question of this study? Does inspiratory resistance breathing improve tolerance to simulated haemorrhage in individuals with elevated internal temperatures? What is the main finding and its importance? The main finding of this study is that inspiratory resistance breathing modestly improves tolerance to a simulated progressive haemorrhagic challenge during heat stress. These findings demonstrate a scenario in which exploitation of the respiratory pump can ameliorate serious conditions related to systemic hypotension. ABSTRACT Heat exposure impairs human blood pressure control and markedly reduces tolerance to a simulated haemorrhagic challenge. Inspiratory resistance breathing enhances blood pressure control and improves tolerance during simulated haemorrhage in normothermic individuals. However, it is unknown whether similar improvements occur with this manoeuvre in heat stress conditions. In this study, we tested the hypothesis that inspiratory resistance breathing improves tolerance to simulated haemorrhage in individuals with elevated internal temperatures. On two separate days, eight subjects performed a simulated haemorrhage challenge [lower-body negative pressure (LBNP)] to presyncope after an increase in internal temperature of 1.3 ± 0.1°C. During one trial, subjects breathed through an inspiratory impedance device set at 0 cmH2 O of resistance (Sham), whereas on a subsequent day the device was set at -7 cmH2 O of resistance (ITD). Tolerance was quantified as the cumulative stress index. Subjects were more tolerant to the LBNP challenge during the ITD protocol, as indicated by a > 30% larger cumulative stress index (Sham, 520 ± 306 mmHg min; ITD, 682 ± 324 mmHg min; P < 0.01). These data indicate that inspiratory resistance breathing modestly improves tolerance to a simulated progressive haemorrhagic challenge during heat stress.
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Affiliation(s)
- Mu Huang
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas, TX, USA
- Department of Health Care Sciences, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - R Matthew Brothers
- Department of Kinesiology, University of Texas, Arlington, Arlington, TX, USA
| | - Matthew S Ganio
- Department of Health, Human Performance and Recreation, University of Arkansas, Fayetteville, AR, USA
| | - Rebekah A I Lucas
- School of Sport, Exercise & Rehabilitation Sciences, The University of Birmingham, Edgbaston, Birmingham, UK
| | - Matthew N Cramer
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas, TX, USA
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Gilbert Moralez
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas, TX, USA
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | | | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas, TX, USA
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
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23
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Lucas RAI, Wilson LC, Ainslie PN, Fan JL, Thomas KN, Cotter JD. Independent and interactive effects of incremental heat strain, orthostatic stress, and mild hypohydration on cerebral perfusion. Am J Physiol Regul Integr Comp Physiol 2017; 314:R415-R426. [PMID: 29212807 DOI: 10.1152/ajpregu.00109.2017] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The purpose of this study was to identify the dose-dependent effects of heat strain and orthostasis [via lower body negative pressure (LBNP)], with and without mild hypohydration, on systemic function and cerebral perfusion. Eleven men (means ± SD: 27 ± 7 y; body mass 77 ± 6 kg), resting supine in a water-perfused suit, underwent progressive passive heating [0.5°C increments in core temperature (Tc; esophageal to +2.0°C)] while euhydrated (EUH) or hypohydrated (HYPO; 1.5-2% body mass deficit). At each thermal state, mean cerebral artery blood velocity (MCAvmean; transcranial Doppler), partial pressure of end-tidal carbon dioxide ([Formula: see text]), heart rate (HR) and mean arterial blood pressure (MAP; photoplethysmography) were measured continuously during LBNP (0, -15, -30, and -45 mmHg). Four subjects became intolerant before +2.0°C Tc, unrelated to hydration status. Without LBNP, decreases in [Formula: see text] accounted fully for reductions in MCAvmean across all Tc. With LBNP at heat tolerance (+1.5 or +2.0°C), [Formula: see text] accounted for 69 ± 25% of the change in MCAvmean. The HYPO condition did not affect MCAvmean or any cardiovascular variables during combined LBNP and passive heat stress (all P > 0.13). These findings indicate that hypocapnia accounted fully for the reduction in MCAvmean when passively heat stressed in the absence of LBNP and for two- thirds of the reduction when at heat tolerance combined with LBNP. Furthermore, when elevations in Tc are matched, mild hypohydration does not influence cerebrovascular or cardiovascular responses to LBNP, even when stressed by a combination of hyperthermia and LBNP.
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Affiliation(s)
- R A I Lucas
- Department of Physiology, University of Otago , Dunedin , New Zealand.,School of Physical Education, Sport and Exercise Sciences, University of Otago , Dunedin , New Zealand.,School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham , Birmingham , United Kingdom
| | - L C Wilson
- Department of Physiology, University of Otago , Dunedin , New Zealand.,School of Physical Education, Sport and Exercise Sciences, University of Otago , Dunedin , New Zealand.,Department of Medicine, University of Otago , Dunedin , New Zealand
| | - P N Ainslie
- Department of Physiology, University of Otago , Dunedin , New Zealand.,Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia Okanagan , Kelowna , Canada
| | - J L Fan
- Department of Physiology, University of Otago , Dunedin , New Zealand.,Institute of Sports Science, Faculty of Biology and Medicine, University of Lausanne , Lausanne , Switzerland.,Lemanic Neuroscience Doctoral School, University of Lausanne , Lausanne , Switzerland
| | - K N Thomas
- Department of Physiology, University of Otago , Dunedin , New Zealand.,School of Physical Education, Sport and Exercise Sciences, University of Otago , Dunedin , New Zealand.,Department of Surgical Sciences, Dunedin School of Medicine, University of Otago . New Zealand
| | - J D Cotter
- School of Physical Education, Sport and Exercise Sciences, University of Otago , Dunedin , New Zealand
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Wegman DH, Apelqvist J, Bottai M, Ekström U, García-Trabanino R, Glaser J, Hogstedt C, Jakobsson K, Jarquín E, Lucas RAI, Weiss I, Wesseling C, Bodin T. Intervention to diminish dehydration and kidney damage among sugarcane workers. Scand J Work Environ Health 2017; 44:16-24. [PMID: 28691728 DOI: 10.5271/sjweh.3659] [Citation(s) in RCA: 61] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Objective The aim of this study was to assess the potential to reduce kidney function damage during the implementation of a water, rest, shade (WRS) and efficiency intervention program among sugarcane workers. Methods A WRS intervention program adapted from the US Occupational Safety and Health Administration (OSHA) coupled with an efficiency program began two months into the 5-month harvest. One of the two groups of workers studied was provided with portable water reservoirs, mobile shaded tents, and scheduled rest periods. Health data (anthropometric and questionnaires), blood, and urine were collected at baseline and at three subsequent times over the course of the harvest. Daily wet bulb globe temperatures (WBGT) were recorded. Results Across a working day there were changes in biomarkers indicating dehydration (urine osmolality) and serum albumin and reduced estimated glomerular filtration rate (eGFR). Cross-shift eGFR decrease was present in both groups; -10.5 mL/min/1.73m2 [95% confidence interval (95% CI) -11.8- -9.1], but smaller for the intervention group after receiving the program. Decreased eGFR over the 5-month harvest was seen in both groups: in the one receiving the intervention -3.4 mL/min/1.73m 2(95% CI -5.5- -1.3) and in the other -5.3 (95% CI -7.9- -2.7). The decrease appeared to halt after the introduction of the intervention in the group receiving the program. Conclusion A WRS and efficiency intervention program was successfully introduced for workers in sugarcane fields and appears to reduce the impact of heat stress on acute and over-harvest biomarkers of kidney function. Further research is needed to determine whether biomarker changes predict reduced risk of chronic kidney disease in this type of work.
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Affiliation(s)
- David H Wegman
- University of Massachusetts Lowell, 7 Camden Place, Cambridge, MA 02138, USA.
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Quam VGM, Rocklöv J, Quam MBM, Lucas RAI. Assessing Greenhouse Gas Emissions and Health Co-Benefits: A Structured Review of Lifestyle-Related Climate Change Mitigation Strategies. Int J Environ Res Public Health 2017; 14:ijerph14050468. [PMID: 28448460 PMCID: PMC5451919 DOI: 10.3390/ijerph14050468] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Revised: 04/12/2017] [Accepted: 04/13/2017] [Indexed: 11/24/2022]
Abstract
This is the first structured review to identify and summarize research on lifestyle choices that improve health and have the greatest potential to mitigate climate change. Two literature searches were conducted on: (1) active transport health co-benefits, and (2) dietary health co-benefits. Articles needed to quantify both greenhouse gas emissions and health or nutrition outcomes resulting from active transport or diet changes. A data extraction tool (PRISMA) was created for article selection and evaluation. A rubric was devised to assess the biases, limitations and uncertainties of included articles. For active transport 790 articles were retrieved, nine meeting the inclusion criteria. For diet 2524 articles were retrieved, 23 meeting the inclusion criteria. A total of 31 articles were reviewed and assessed using the rubric, as one article met the inclusion criteria for both active transport and diet co-benefits. Methods used to estimate the effect of diet or active transport modification vary greatly precluding meta-analysis. The scale of impact on health and greenhouse gas emissions (GHGE) outcomes depends predominately on the aggressiveness of the diet or active transport scenario modelled, versus the modelling technique. Effective mitigation policies, infrastructure that supports active transport and low GHGE food delivery, plus community engagement are integral in achieving optimal health and GHGE outcomes. Variation in culture, nutritional and health status, plus geographic density will determine which mitigation scenario(s) best suit individual communities.
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Affiliation(s)
- Vivian G M Quam
- Department of Public Health and Clinical Medicine, Epidemiology and Global Health, Umeå University, 901 87 Umeå, Sweden.
- College of Veterinary Medicine, University of Georgia, Athens, GA 30602, USA.
| | - Joacim Rocklöv
- Department of Public Health and Clinical Medicine, Epidemiology and Global Health, Umeå University, 901 87 Umeå, Sweden.
| | - Mikkel B M Quam
- Department of Public Health and Clinical Medicine, Epidemiology and Global Health, Umeå University, 901 87 Umeå, Sweden.
| | - Rebekah A I Lucas
- Department of Public Health and Clinical Medicine, Epidemiology and Global Health, Umeå University, 901 87 Umeå, Sweden.
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham B15 2TT, UK.
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26
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Pearson J, Lucas RAI, Schlader ZJ, Gagnon D, Crandall CG. Elevated skin and core temperatures both contribute to reductions in tolerance to a simulated haemorrhagic challenge. Exp Physiol 2017; 102:255-264. [PMID: 27981648 DOI: 10.1113/ep085896] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Accepted: 12/01/2016] [Indexed: 12/20/2022]
Abstract
NEW FINDINGS What is the central question of this study? Combined increases in skin and core temperatures reduce tolerance to a simulated haemorrhagic challenge. The aim of this study was to examine the separate and combined influences of increased skin and core temperatures upon tolerance to a simulated haemorrhagic challenge. What is the main finding and its importance? Skin and core temperatures increase during many occupational settings, including military procedures, in hot environments. The study findings demonstrate that both increased skin temperature and increased core temperature can impair tolerance to a simulated haemorrhagic challenge; therefore, a soldier's tolerance to haemorrhagic injury is likely to be impaired during any military activity that results in increased skin and/or core temperatures. Tolerance to a simulated haemorrhagic insult, such as lower-body negative pressure (LBNP), is profoundly reduced when accompanied by whole-body heat stress. The aim of this study was to investigate the separate and combined influence of elevated skin (Tskin ) and core temperatures (Tcore ) on LBNP tolerance. We hypothesized that elevations in Tskin as well as Tcore would both contribute to reductions in LBNP tolerance and that the reduction in LBNP tolerance would be greatest when both Tskin and Tcore were elevated. Nine participants underwent progressive LBNP to presyncope on four occasions, as follows: (i) control, with neutral Tskin (34.3 ± 0.5°C) and Tcore (36.8 ± 0.2°C); (ii) primarily skin hyperthermia, with high Tskin (37.6 ± 0.2°C) and neutral Tcore (37.1 ± 0.2°C); (iii) primarily core hyperthermia, with neutral Tskin (35.0 ± 0.5°C) and high Tcore (38.3 ± 0.2°C); and (iv) combined skin and core hyperthermia, with high Tskin (38.8 ± 0.6°C) and high Tcore (38.1 ± 0.2°C). The LBNP tolerance was quantified via the cumulative stress index (in millimetres of mercury × minutes). The LBNP tolerance was reduced during the skin hyperthermia (569 ± 151 mmHg min) and core hyperthermia trials (563 ± 194 mmHg min) relative to control conditions (1010 ± 246 mmHg min; both P < 0.05). However, LBNP tolerance did not differ between skin hyperthermia and core hyperthermia trials (P = 0.92). The lowest LBNP tolerance was observed during combined skin and core hyperthermia (257 ± 106 mmHg min; P < 0.05 relative to all other trials). These data indicate that elevated skin temperature, as well as elevated core temperature, can both contribute to reductions in LBNP tolerance in heat-stressed individuals. However, heat stress-induced reductions in LBNP tolerance are greatest in conditions when both skin and core temperatures are elevated.
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Affiliation(s)
- James Pearson
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas and Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas.,Department of Biology, University of Colorado at Colorado Springs, Colorado, USA
| | - Rebekah A I Lucas
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas and Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas.,School of Sport, Exercise and Rehabilitation Sciences, The University of Birmingham, Edgbaston, Birmingham, UK
| | - Zachary J Schlader
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas and Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas.,Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York, USA
| | - Daniel Gagnon
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas and Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas and Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas
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Ganio MS, Schlader ZJ, Pearson J, Lucas RAI, Gagnon D, Rivas E, Kowalske KJ, Crandall CG. Nongrafted Skin Area Best Predicts Exercise Core Temperature Responses in Burned Humans. Med Sci Sports Exerc 2016; 47:2224-32. [PMID: 26378947 DOI: 10.1249/mss.0000000000000655] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
UNLABELLED Grafted skin impairs heat dissipation, but it is unknown to what extent this affects body temperature during exercise in the heat. PURPOSE We examined core body temperature responses during exercise in the heat in a group of individuals with a large range of grafts covering their body surface area (BSA; 0%-75%). METHODS Forty-three individuals (19 females) were stratified into groups based on BSA grafted: control (0% grafted, n = 9), 17%-40% (n = 19), and >40% (n = 15). Subjects exercised at a fixed rate of metabolic heat production (339 ± 70 W; 4.3 ± 0.8 W·kg) in an environmental chamber set at 40°C, 30% relative humidity for 90 min or until exhaustion (n = 8). Whole-body sweat rate and core temperatures were measured. RESULTS Whole-body sweat rates were similar between the groups (control: 14.7 ± 3.4 mL·min, 17%-40%: 12.6 ± 4.0 mL·min; and >40%: 11.7 ± 4.4 mL·min; P > 0.05), but the increase in core temperature at the end of exercise in the >40% BSA grafted group (1.6°C ± 0.5°C) was greater than the 17%-40% (1.2°C ± 0.3°C) and control (0.9°C ± 0.2°C) groups (P < 0.05). Absolute BSA of nongrafted skin (expressed in square meters) was the strongest independent predictor of the core temperature increase (r = 0.41). When regrouping all subjects, individuals with the lowest BSA of nongrafted skin (<1.0 m) had greater increases in core temperature (1.6°C ± 0.5°C) than those with more than 1.5 m nongrafted skin (1.0°C ± 0.3°C; P < 0.05). CONCLUSIONS These data imply that individuals with grafted skin have greater increases in core temperature when exercising in the heat and that the magnitude of this increase is best explained by the amount of nongrafted skin available for heat dissipation.
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Affiliation(s)
- Matthew S Ganio
- 1Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas, TX; and Department of Internal Medicine University of Texas Southwestern Medical Center, Dallas, TX; 2Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, AR; 3Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY; 4Department of Biology, University of Colorado - Colorado Springs, Colorado Springs, CO; 5Center for Global Health Research, Umeå University, Umeå, SWEDEN; 6Department of Kinesiology, Texas Woman's University, Denton, TX; 7Department of Physical Medicine and Rehabilitation, University of Texas Southwestern Medical Center, Dallas, TX
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Bodin T, García-Trabanino R, Weiss I, Jarquín E, Glaser J, Jakobsson K, Lucas RAI, Wesseling C, Hogstedt C, Wegman DH. Intervention to reduce heat stress and improve efficiency among sugarcane workers in El Salvador: Phase 1. Occup Environ Med 2016; 73:409-16. [PMID: 27073211 PMCID: PMC4893112 DOI: 10.1136/oemed-2016-103555] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Accepted: 03/24/2016] [Indexed: 11/04/2022]
Abstract
BACKGROUND Chronic heat stress and dehydration from strenuous work in hot environments is considered an essential component of the epidemic of chronic kidney disease in Central America. OBJECTIVE (1) To assess feasibility of providing an intervention modelled on OSHA's Water.Rest.Shade programme (WRS) during sugarcane cutting and (2) to prevent heat stress and dehydration without decreasing productivity. METHODS Midway through the 6-month harvest, the intervention introduced WRS practices. A 60-person cutting group was provided water supplied in individual backpacks, mobile shaded rest areas and scheduled rest periods. Ergonomically improved machetes and efficiency strategies were also implemented. Health data (anthropometric, blood, urine, questionnaires) were collected preharvest, preintervention, mid-intervention and at the end of harvest. A subsample participated in focus group discussions. Daily wet bulb globe temperatures (WBGT) were recorded. The employer provided individual production records. RESULTS Over the harvest WBGT was >26°C from 9:00 onwards reaching average maximum of 29.3±1.7°C, around 13:00. Postintervention self-reported water consumption increased 25%. Symptoms associated with heat stress and with dehydration decreased. Individual daily production increased from 5.1 to a high of 7.3 tons/person/day postintervention. This increase was greater than in other cutting groups at the company. Focus groups reported a positive perception of components of the WRS, and the new machete and cutting programmes. CONCLUSIONS A WRS intervention is feasible in sugarcane fields, and appears to markedly reduce the impact of the heat stress conditions for the workforce. With proper attention to work practices, production can be maintained with less impact on worker health.
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Affiliation(s)
- T Bodin
- Institute of Environmental Medicine, Karolinska Institute, Stockholm, Sweden
| | - R García-Trabanino
- Association of Nephrology and Hypertension of El Salvador, San Salvador, El Salvador
| | - I Weiss
- La Isla Foundation, Ada, Michigan, USA
| | - E Jarquín
- Agency for Development and Agricultural Health (AGDYSA), San Salvador, El Salvador
| | - J Glaser
- La Isla Foundation, Ada, Michigan, USA
| | - K Jakobsson
- Department of Public Health and Community Medicine, Gothenburg University, Gothenburg, Sweden
| | - R A I Lucas
- School of Sport, Exercise & Rehabilitation Sciences, University of Birmingham, Birmingham, UK
| | - C Wesseling
- Institute of Environmental Medicine, Karolinska Institute, Stockholm, Sweden
| | - C Hogstedt
- Institute of Environmental Medicine, Karolinska Institute, Stockholm, Sweden
| | - D H Wegman
- Department of Work Environment, University of Massachusetts Lowell, Lowell, Massachusetts, USA
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Lucas RAI, Pearson J, Schlader ZJ, Crandall CG. Cardiopulmonary and arterial baroreceptor unloading during passive hyperthermia does not contribute to hyperthermia-induced hyperventilation. Exp Physiol 2015; 100:1309-18. [PMID: 26299270 DOI: 10.1113/ep085259] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Accepted: 08/18/2015] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the central question of this study? Does baroreceptor unloading during passive hyperthermia contribute to increases in ventilation and decreases in end-tidal carbon dioxide during that exposure? What is the main finding and its importance? Hyperthermic hyperventilation is not mitigated by expanding central blood volume and reloading the cardiopulmonary baroreceptors via rapid saline infusion or by reloading the arterial baroreceptors via phenylephrine administration. The absence of a reduction in ventilation upon reloading the baroreceptors to pre-hyperthermic levels indicates that cardiopulmonary and arterial baroreceptor unloading with hyperthermia is unlikely to contribute to hyperthermic hyperventilation in humans. This study tested the hypothesis that baroreceptor unloading during passive hyperthermia contributes to increases in ventilation and decreases in end-tidal partial pressure of carbon dioxide (P ET ,CO2) during that exposure. Two protocols were performed, in which healthy subjects underwent passive hyperthermia (increasing intestinal temperature by ∼1.8°C) to cause a sustained increase in ventilation and reduction in P ET ,CO2. Upon attaining hyperthermic hyperventilation, in protocol 1 (n = 10; three females) a bolus (19 ± 2 ml kg(-1) ) of warm (∼38°C) isotonic saline was rapidly (5-10 min) infused intravenously to restore reductions in central venous pressure, whereas in protocol 2 (n = 11; five females) phenylephrine was infused intravenously (60-120 μg min(-1) ) to return mean arterial pressure to normothermic levels. In protocol 1, hyperthermia increased ventilation (by 2.2 ± 1.7 l min(-1) , P < 0.01), while reducing P ET ,CO2 (by 4 ± 3 mmHg, P = 0.04) and central venous pressure (by 5 ± 1 mmHg, P <0.01). Saline infusion increased central venous pressure by 5 ± 1 mmHg (P < 0.01), restoring it to normothermic values, but did not change ventilation or P ET ,CO2 (P > 0.05). In protocol 2, hyperthermia increased ventilation (by 5.0 ± 2.7 l min(-1) , P <0.01) and reduced P ET ,CO2 (by 5 ± 2 mmHg, P < 0.01) and mean arterial pressure (by 9 ± 7 mmHg, P <0.01). Phenylephrine infusion increased mean arterial pressure by 12 ± 3 mmHg (P < 0.01), restoring it to normothermic values, but did not change ventilation or P ET ,CO2 (P > 0.05). The absence of a reduction in ventilation upon reloading the cardiopulmonary and arterial baroreceptors to pre-hyperthermic levels indicates that baroreceptor unloading with hyperthermia is unlikely to contribute to hyperthermic hyperventilation in humans.
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Affiliation(s)
- Rebekah A I Lucas
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas, TX, USA.,School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK
| | - James Pearson
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas, TX, USA.,Department of Biology, University of Colorado at Colorado Springs, Colorado Springs, CO, USA
| | - Zachary J Schlader
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas, TX, USA.,Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, USA
| | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas, TX, USA
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Schlader ZJ, Ganio MS, Pearson J, Lucas RAI, Gagnon D, Rivas E, Kowalske KJ, Crandall CG. Heat acclimation improves heat exercise tolerance and heat dissipation in individuals with extensive skin grafts. J Appl Physiol (1985) 2015; 119:69-76. [PMID: 25930025 DOI: 10.1152/japplphysiol.00176.2015] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2015] [Accepted: 04/23/2015] [Indexed: 11/22/2022] Open
Abstract
Burn survivors with extensive skin grafts have impaired heat dissipation and thus heat tolerance. This study tested the hypothesis that heat acclimation (HA) improves these factors in this population. Thirty-four burn survivors were stratified into highly [>40% body surface area (BSA) grafted, n = 15] and moderately (17-40% BSA grafted, n = 19) grafted groups. Nine healthy nonburned subjects served as controls. Subjects underwent 7 days of HA involving 90 min of exercise at ∼ 50% peak oxygen uptake in 40°C, 30% relative humidity. On days 1 and 7, subjects exercised in the heat at a fixed rate of metabolic heat production. Pre-HA, all controls and 18/19 subjects in the 17-40% group completed 90 min of exercise. Conversely, heat exercise tolerance was lower (P < 0.01) in the > 40% group, with 7/15 subjects not completing 90 min of exercise. Post-HA, heat exercise tolerance was similar between groups (P = 0.39) as all subjects, except one, completed 90 min of exercise. Pre-HA, the magnitude of the increase in internal temperature during exercise occurred sequentially (P ≤ 0.03) according to BSA grafted (>40%: 1.6 ± 0.5°C; 17-40%: 1.2 ± 0.3°C; control: 0.9 ± 0.2°C). HA attenuated (P < 0.01) increases in internal temperature in the control (by 0.2 ± 0.3°C), 17-40% (by 0.3 ± 0.3°C), and > 40% (by 0.3 ± 0.4°C) groups, the magnitude of which was similar between groups (P = 0.42). These data indicate that HA improves heat tolerance and dissipation in burn survivors with grafted skin, and the magnitude of these improvements are not influenced by the extent of skin grafting.
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Affiliation(s)
- Zachary J Schlader
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas and Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas; Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York
| | - Matthew S Ganio
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas and Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas; Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas
| | - James Pearson
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas and Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas; Department of Biology, University of Colorado at Colorado Springs, Colorado
| | - Rebekah A I Lucas
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas and Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas; School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK
| | - Daniel Gagnon
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas and Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Eric Rivas
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas and Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas; Department of Kinesiology, Texas Woman's University, Denton, Texas; and
| | - Karen J Kowalske
- Department of Physical Medicine and Rehabilitation, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas and Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas;
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Schlader ZJ, Gagnon D, Lucas RAI, Pearson J, Crandall CG. Baroreceptor unloading does not limit forearm sweat rate during severe passive heat stress. J Appl Physiol (1985) 2015; 118:449-54. [PMID: 25525210 DOI: 10.1152/japplphysiol.00800.2014] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This study tested the hypothesis that sweat rate during passive heat stress is limited by baroreceptor unloading associated with heat stress. Two protocols were performed in which healthy subjects underwent passive heat stress that elicited an increase in intestinal temperature of ∼1.8°C. Upon attaining this level of hyperthermia, in protocol 1 (n = 10, 3 females) a bolus (19 ml/kg) of warm (∼38°C) isotonic saline was rapidly (5-10 min) infused intravenously to elevate central venous pressure (CVP), while in protocol 2 (n = 11, 5 females) phenylephrine was infused intravenously (60-120 μg/min) to return mean arterial pressure (MAP) to normothermic levels. In protocol 1, heat stress reduced CVP from 3.9 ± 1.9 mmHg (normothermia) to -0.6 ± 1.4 mmHg (P < 0.001), while saline infusion returned CVP to normothermic levels (5.1 ± 1.7 mmHg; P > 0.999). Sweat rate was elevated by heat stress (1.21 ± 0.44 mg·cm(-2)·min(-1)) but remained unchanged during rapid saline infusion (1.26 ± 0.47 mg·cm(-2)·min(-1), P = 0.5), whereas cutaneous vascular conductance increased from 77 ± 10 to 101 ± 20% of local heating max (P = 0.029). In protocol 2, MAP was reduced with heat stress from 85 ± 7 mmHg to 76 ± 8 mmHg (P = 0.048). Although phenylephrine infusion returned MAP to normothermic levels (88 ± 7 mmHg; P > 0.999), sweat rate remained unchanged during phenylephrine infusion (1.39 ± 0.22 vs. 1.41 ± 0.24 mg·cm(-2)·min(-1); P > 0.999). These data indicate that both cardiopulmonary and arterial baroreceptor unloading do not limit increases in sweat rate during passive heat stress.
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Affiliation(s)
- Zachary J Schlader
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas, and the University of Texas Southwestern Medical Center, Dallas, Texas; Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York
| | - Daniel Gagnon
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas, and the University of Texas Southwestern Medical Center, Dallas, Texas
| | - Rebekah A I Lucas
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas, and the University of Texas Southwestern Medical Center, Dallas, Texas; Department of Public Health and Clinical Medicine, Umeå University, Umeå Sweden; and
| | - James Pearson
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas, and the University of Texas Southwestern Medical Center, Dallas, Texas; Department of Biology, University of Colorado at Colorado Springs, Colorado Springs, Colorado
| | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas, and the University of Texas Southwestern Medical Center, Dallas, Texas;
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Lucas RAI, Sarma S, Schlader ZJ, Pearson J, Crandall CG. Age-related changes to cardiac systolic and diastolic function during whole-body passive hyperthermia. Exp Physiol 2015; 100:422-34. [PMID: 25641368 DOI: 10.1113/expphysiol.2014.083014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2014] [Accepted: 01/13/2015] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the central question of this study? The effect of ageing on hyperthermia-induced changes in cardiac function is unknown. What is the main finding and its importance? Using echocardiography, we show that during hyperthermia the systolic and diastolic function can be appropriately augmented to meet cardiac demand in healthy older adults, although overall age-related impairments remain. One exception was late diastolic ventricular filling [i.e. E/A ratio and A/(A + E) ratio], which in the older adults was not further augmented during hyperthermia, unlike their young counterparts. To meet cardiac demand, therefore, healthy older adults appear to depend on an increased left ventricular systolic strain and proportion of their cardiac reserve. The effect of ageing on hyperthermia-induced changes in cardiac function is unknown. This study tested the hypothesis that hyperthermia-induced changes in left ventricular systolic and diastolic function are attenuated in older adults when compared with young adults. Eight older (71 ± 5 years old) and eight young adults (29 ± 5 years old), matched for sex, physical activity and body mass index, underwent whole-body passive hyperthermia. Mean arterial pressure (Finometer Pro), heart rate, forearm vascular conductance (venous occlusion plethysmography) and echocardiographic indices of diastolic and systolic function were measured during a normothermic supine period and again after an increase in internal temperature of ∼1.0 °C. Hyperthermia decreased mean arterial pressure and left ventricular end-diastolic volumes and increased heart rate to a similar extent in both groups (P > 0.05). Ageing did not alter the magnitude of hyperthermia-induced changes in indices of systolic (lateral mitral annular S' velocity) or diastolic function (lateral mitral annular E' velocity, peak early diastolic filling and isovolumic relaxation time; P > 0.05). However, with hyperthermia the global longitudinal systolic strain increased in the older group, but was unchanged in the young group (P = 0.03). Also, older adults were unable to augment late diastolic ventricular filling [i.e. E/A ratio and A/(A + E) ratio] during hyperthermia, unlike the young (P < 0.05). These findings indicate that older adults depend on a greater systolic contribution (global longitudinal systolic strain) to meet hyperthermic demand and that the atrial contribution to diastolic filling was not further augmented in older adults when compared with young adults.
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Affiliation(s)
- Rebekah A I Lucas
- University of Texas Southwestern Medical Center, Dallas, TX, USA; Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas, TX, USA; Department of Public Health and Clinical Medicine, Division of Epidemiology and Global Health, Umeå University, Umeå, Sweden
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Burgess KR, Lucas SJE, Shepherd K, Dawson A, Swart M, Thomas KN, Lucas RAI, Donnelly J, Peebles KC, Basnyat R, Ainslie PN. Influence of cerebral blood flow on central sleep apnea at high altitude. Sleep 2014; 37:1679-87. [PMID: 25197804 DOI: 10.5665/sleep.4080] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2013] [Accepted: 03/14/2014] [Indexed: 11/03/2022] Open
Abstract
STUDY OBJECTIVES To further our understanding of central sleep apnea (CSA) at high altitude during acclimatization, we tested the hypothesis that pharmacologically altering cerebral blood flow (CBF) would alter the severity of CSA at high altitude. DESIGN The study was a randomized, placebo-controlled single-blind study. SETTING A field study at 5,050 m in Nepal. PATIENTS OR PARTICIPANTS We studied 12 normal volunteers. INTERVENTIONS Between days 5 to 10 at high altitude, CBF velocity (CBFv) was increased by intravenous (IV) acetazolamide (10 mg/kg) and reduced by oral indomethacin (100 mg). MEASUREMENTS AND RESULTS Arterial blood gases, hypoxic and hypercapnic ventilatory responses, and CBFv and its reactivity to carbon dioxide were measured awake. Overnight polysomnography was performed. The central apnea-hypopnea index was elevated following administration of indomethacin (89.2 ± 43.7 to 112.5 ± 32.9 events/h; mean ± standard deviation; P < 0.05) and was reduced following IV acetazolamide (89.2 ± 43.7 to 47.1 ± 48.1 events/h; P < 0.001). Intravenous acetazolamide elevated CBFv at high altitude by 28% (95% confidence interval [CI]: 22-34%) but did not affect ventilatory responses. The elevation in CBFv was partly mediated via a selective rise in partial pressure of arterial carbon dioxide (PaCO2) (28 ± 4 to 31 ± 3 mm Hg) and an associated fall in pH (P < 0.01). Oral indomethacin reduced CBFv by 23% (95% CI: 16-30%), blunted CBFv reactivity, and increased the hypercapnic ventilatory response by 66% (95% CI: 30-102%) but had no effect on PaCO2 or pH. CONCLUSION Our findings indicate an important role for cerebral blood flow regulation in the pathophysiology of central sleep apnea at high altitude.
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Affiliation(s)
- Keith R Burgess
- Peninsula Sleep Laboratory, Sydney, New South Wales, Australia and Department of Medicine, University of Sydney, Sydney, New South Wales, Australia
| | | | - Kelly Shepherd
- Peninsula Sleep Laboratory, Sydney, New South Wales, Australia
| | - Andrew Dawson
- Peninsula Sleep Laboratory, Sydney, New South Wales, Australia
| | - Marianne Swart
- Peninsula Sleep Laboratory, Sydney, New South Wales, Australia
| | | | | | | | | | - Rishi Basnyat
- Nepal International Clinic, Kathmandu, Nepal and Banner Good Samaritan Medical Center, Phoenix, Arizona
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Canada
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Abstract
New Findings What is the central question of this study? The relationship between changes in cerebral blood flow and arterial carbon dioxide tension is used to assess cerebrovascular function. Hypercapnia is generally evoked by two methods, i.e. steady-state and transient increases in carbon dioxide tension. In some cases, the hypercapnia is immediately preceded by a period of hypocapnia. It is unknown whether the cerebrovascular response differs between these methods and whether a period of hypocapnia blunts the subsequent response to hypercapnia. What is the main finding and its importance? The cerebrovascular response is similar between steady-state and transient hypercapnia. However, hyperventilation-induced hypocapnia attenuates the cerebral vasodilatory responses during a subsequent period of rebreathing-induced hypercapnia.
Cerebral vasomotor reactivity (CVMR) to changes in arterial carbon dioxide tension () is assessed during steady-state or transient changes in . This study tested the following two hypotheses: (i) that CVMR during steady-state changes differs from that during transient changes in ; and (ii) that CVMR during rebreathing-induced hypercapnia would be blunted when preceded by a period of hyperventilation. For each hypothesis, end-tidal carbon dioxide tension () middle cerebral artery blood velocity (CBFV), cerebrovascular conductance index (CVCI; CBFV/mean arterial pressure) and CVMR (slope of the linear regression between changes in CBFV and CVCI versus) were assessed in eight individuals. To address the first hypothesis, measurements were made during the following two conditions (randomized): (i) steady-state increases in of 5 and 10 Torr above baseline; and (ii) rebreathing-induced transient breath-by-breath increases in . The linear regression for CBFV versus (P = 0.65) and CVCI versus (P = 0.44) was similar between methods; however, individual variability in CBFV or CVCI responses existed among subjects. To address the second hypothesis, the same measurements were made during the following two conditions (randomized): (i) immediately following a brief period of hypocapnia induced by hyperventilation for 1 min followed by rebreathing; and (ii) during rebreathing only. The slope of the linear regression for CBFV versus (P < 0.01) and CVCI versus (P < 0.01) was reduced during hyperventilation plus rebreathing relative to rebreathing only. These results indicate that cerebral vasomotor reactivity to changes in is similar regardless of the employed methodology to induce changes in and that hyperventilation-induced hypocapnia attenuates the cerebral vasodilatory responses during a subsequent period of rebreathing-induced hypercapnia.
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Affiliation(s)
- R Matthew Brothers
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, TX, USA Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA Department of Kinesiology and Health Education, University of Texas at Austin, TX, USA
| | - Rebekah A I Lucas
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, TX, USA Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Yong-Sheng Zhu
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, TX, USA Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, TX, USA Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Rong Zhang
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, TX, USA Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
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Lucas RAI, Pearson J, Schlader ZJ, Crandall CG. Hypercapnia-induced increases in cerebral blood flow do not improve lower body negative pressure tolerance during hyperthermia. Am J Physiol Regul Integr Comp Physiol 2013; 305:R604-9. [PMID: 23864641 DOI: 10.1152/ajpregu.00052.2013] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Heat-related decreases in cerebral perfusion are partly the result of ventilatory-related reductions in arterial CO2 tension. Cerebral perfusion likely contributes to an individual's tolerance to a challenge like lower body negative pressure (LBNP). Thus increasing cerebral perfusion may prolong LBNP tolerance. This study tested the hypothesis that a hypercapnia-induced increase in cerebral perfusion improves LBNP tolerance in hyperthermic individuals. Eleven individuals (31 ± 7 yr; 75 ± 12 kg) underwent passive heat stress (increased intestinal temperature ∼1.3°C) followed by a progressive LBNP challenge to tolerance on two separate days (randomized). From 30 mmHg LBNP, subjects inhaled either (blinded) a hypercapnic gas mixture (5% CO2, 21% oxygen, balanced nitrogen) or room air (SHAM). LBNP tolerance was quantified via the cumulative stress index (CSI). Mean middle cerebral artery blood velocity (MCAvmean,) and end-tidal CO2 (PetCO2) were also measured. CO2 inhalation of 5% increased PetCO2 at ∼40 mmHg LBNP (by 16 ± 4 mmHg) and at LBNP tolerance (by 18 ± 5 mmHg) compared with SHAM (P < 0.01). Subsequently, MCAvmean was higher in the 5% CO2 trial during ∼40 mmHg LBNP (by 21 ± 12 cm/s, ∼31%) and at LBNP tolerance (by 18 ± 10 cm/s, ∼25%) relative to the SHAM (P < 0.01). However, hypercapnia-induced increases in MCAvmean did not alter LBNP tolerance (5% CO2 CSI: 339 ± 155 mmHg × min; SHAM CSI: 273 ± 158 mmHg × min; P = 0.26). These data indicate that inhaling a hypercapnic gas mixture increases cerebral perfusion during LBNP but does not improve LBNP tolerance when hyperthermic.
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Affiliation(s)
- Rebekah A I Lucas
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas, Texas and Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas
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Abstract
This study tested the hypothesis that hyperthermia attenuates the increase in cerebral perfusion during cognitive activation. Mean middle cerebral artery blood velocity (MCAV(mean)) served as an index of cerebral perfusion, while the nBack test (a test of working memory) was the cognitive task. Hyperthermia was characterized by elevations (P < 0.001) in skin (by 5.0 ± 0.8 °C) and intestinal temperatures (by 1.3 ± 0.1 °C) and reductions (P < 0.020) in mean arterial pressure (by 11 ± 10 mmHg), end-tidal CO2 tension (by 3 ± 6 mmHg) and MCAV(mean) (by 10 ± 9 cm s(-1)). Hyperthermia had no influence on nBack test performance (mean difference from normothermia to hyperthermia, -1 ± 11%; P = 0.276) or, counter to the hypothesis, the increase in MCAV(mean) during nBack testing (mean difference from normothermia to hyperthermia: 0 ± 16 cm s(-1); P = 0.608). These findings indicate that the capacity to increase cerebral perfusion during cognitive activation is unaffected by hyperthermia.
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Affiliation(s)
- Zachary J Schlader
- C. G. Crandall: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, 7232 Greenville Avenue, Dallas, TX 75231, USA.
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Schlader ZJ, Lucas RAI, Pearson J, Crandall CG. One of these things is not like the other: the heterogeneity of the cerebral circulation. J Physiol 2013; 591:395-7. [PMID: 23322292 DOI: 10.1113/jphysiol.2012.244772] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
- Zachary J Schlader
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas, Dallas, TX, USA.
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Pearson J, Ganio MS, Lucas RAI, Babb TG, Crandall CG. Heat stress does not augment ventilatory responses to presyncopal limited lower body negative pressure. Exp Physiol 2013; 98:1156-63. [PMID: 23585326 DOI: 10.1113/expphysiol.2013.072082] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Simulated haemorrhage, e.g. lower body negative pressure (LBNP), reduces central blood volume and mean arterial pressure, while ventilation increases. Passive whole-body heat stress likewise increases ventilation. The objective of this project was to test the hypothesis that ventilatory responses to reductions in central blood volume and arterial pressure during simulated haemorrhage are enhanced when individuals are heat stressed rather than normothermic. Eight healthy men (34 ± 9 years old, 176 ± 6 cm tall and 80.2 ± 4.2 kg body weight) underwent a simulated haemorrhagic challenge via LBNP until presyncope on two separate occasions, namely normothermic control and whole-body heat-stress trials. Baseline ventilation and core and mean skin temperatures were not different between trials (all P > 0.05). Prior to LBNP, heat stress increased core (from 36.8 ± 0.2 to 38.2 ± 0.2°C, P < 0.05) and mean skin temperatures (from 33.9 ± 0.5 to 38.1 ± 0.6°C, P < 0.05), as well as minute ventilation (from 8.01 ± 2.63 to 13.68 ± 6.68 l min(-1), P < 0.01). At presyncope, mean arterial pressure and middle cerebral artery blood velocity decreased in both trials (P < 0.05). At presyncope, ventilation increased to 23.22 ± 6.78 (P < 0.01) and 25.88 ± 10.16 l min(-1) (P < 0.01) in the normothermic and hyperthermic trials, respectively; however, neither the increase in ventilation from the pre-LBNP period nor the absolute ventilation was different between normothermic and hyperthermic trials (P > 0.05). These data suggest that the increase in ventilation during simulated haemorrhage induced via LBNP is not altered in heat-stressed humans.
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Affiliation(s)
- J Pearson
- University of Texas SouthwesternMedical Center at Dallas and Institute for Exercise and EnvironmentalMedicine, Texas Health Presbyterian Hospital at Dallas, TX, USA
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Lucas RAI, Pearson J, Schlader ZJ, Crandall CG. Hyperthermic hyperventilation is not mitigated by cardiopulmonary baroreceptor loading. FASEB J 2013. [DOI: 10.1096/fasebj.27.1_supplement.1201.14] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Rebekah A. I. Lucas
- Texas Health Presbyterian Hospital DallasDallasTX
- University of Texas Southwestern Medical CenterDallasTX
| | - James Pearson
- Texas Health Presbyterian Hospital DallasDallasTX
- Cardiff UniversityCardiffUnited Kingdom
| | - Zachary J Schlader
- Texas Health Presbyterian Hospital DallasDallasTX
- University of Texas Southwestern Medical CenterDallasTX
| | - Craig G Crandall
- Texas Health Presbyterian Hospital DallasDallasTX
- University of Texas Southwestern Medical CenterDallasTX
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Burgess KR, Lucas SJE, Shepherd K, Dawson A, Swart M, Thomas KN, Lucas RAI, Donnelly J, Peebles KC, Basnyat R, Ainslie PN. Worsening of central sleep apnea at high altitude--a role for cerebrovascular function. J Appl Physiol (1985) 2013; 114:1021-8. [PMID: 23429871 DOI: 10.1152/japplphysiol.01462.2012] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Although periodic breathing during sleep at high altitude occurs almost universally, the likely mechanisms and independent effects of altitude and acclimatization have not been clearly reported. Data from 2005 demonstrated a significant relationship between decline in cerebral blood flow (CBF) at sleep onset and subsequent severity of central sleep apnea that night. We suspected that CBF would decline during partial acclimatization. We hypothesized therefore that reductions in CBF and its reactivity would worsen periodic breathing during sleep following partial acclimatization. Repeated measures of awake ventilatory and CBF responsiveness, arterial blood gases during wakefulness. and overnight polysomnography at sea level, upon arrival (days 2-4), and following partial acclimatization (days 12-15) to 5,050 m were made on 12 subjects. The apnea-hypopnea index (AHI) increased from to 77 ± 49 on days 2-4 to 116 ± 21 on days 12-15 (P = 0.01). The AHI upon initial arrival was associated with marked elevations in CBF (+28%, 68 ± 11 to 87 ± 17 cm/s; P < 0.05) and its reactivity to changes in PaCO2 [>90%, 2.0 ± 0.6 to 3.8 ± 1.5 cm·s(-1)·mmHg(-1) hypercapnia and 1.9 ± 0.4 to 4.1 ± 0.9 cm·s(-1)·mmHg(-1) for hypocapnia (P < 0.05)]. Over 10 days, the increases resolved and AHI worsened. During sleep at high altitude large oscillations in mean CBF velocity (CBFv) occurred, which were 35% higher initially (peak CBFv = 96 cm/s vs. peak CBFv = 71 cm/s) than at days 12-15. Our novel findings suggest that elevations in CBF and its reactivity to CO(2) upon initial ascent to high altitude may provide a protective effect on the development of periodic breathing during sleep (likely via moderating changes in central Pco2).
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Affiliation(s)
- Keith R Burgess
- Peninsula Sleep Laboratory, Sydney, New South Wales, Australia.
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Pearson J, Lucas RAI, Crandall CG. Elevated local skin temperature impairs cutaneous vasoconstrictor responses to a simulated haemorrhagic challenge while heat stressed. Exp Physiol 2012; 98:444-50. [PMID: 22903981 DOI: 10.1113/expphysiol.2012.068353] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
During a simulated haemorrhagic challenge, syncopal symptoms develop sooner when individuals are hyperthermic relative to normothermic. This is due, in part, to a large displacement of blood to the cutaneous circulation during hyperthermia, coupled with inadequate cutaneous vasoconstriction during the hypotensive challenge. The influence of local skin temperature on these cutaneous vasoconstrictor responses is unclear. This project tested the hypothesis that local skin temperature modulates cutaneous vasoconstriction during simulated haemorrhage in hyperthermic humans. Eight healthy participants (four men and four women; 32 ± 7 years old; 75.2 ± 10.8 kg) underwent lower-body negative pressure to presyncope while heat stressed via a water-perfused suit sufficiently to increase core temperature by 1.2 ± 0.2 °C. At forearm skin sites distal to the water-perfused suit, local skin temperature was either 35.2 ± 0.6 (mild heating) or 38.2 ± 0.2 °C (moderate heating) throughout heat stress and lower-body negative pressure, and remained at these temperatures until presyncope. The reduction in cutaneous vascular conductance during the final 90 s of lower-body negative pressure, relative to heat-stress baseline, was greatest at the mildly heated site (-10 ± 15% reduction) relative to the moderately heated site (-2 ± 12%; P = 0.05 for the magnitude of the reduction in cutaneous vascular conductance between sites), because vasoconstriction at the moderately heated site was either absent or negligible. In hyperthermic individuals, the extent of cutaneous vasoconstriction during a simulated haemorrhage can be modulated by local skin temperature. In situations where skin temperature is at least 38 °C, as is the case in soldiers operating in warm climatic conditions, a haemorrhagic insult is unlikely to be accompanied by cutaneous vasoconstriction.
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Affiliation(s)
- J Pearson
- University of Texas Southwestern Medical Center at Dallas and Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital at Dallas, TX 75023, USA
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Lucas RAI, Ganio MS, Pearson J, Crandall CG. Sweat loss during heat stress contributes to subsequent reductions in lower-body negative pressure tolerance. Exp Physiol 2012; 98:473-80. [PMID: 22872657 DOI: 10.1113/expphysiol.2012.068171] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The contribution of sweating to heat stress-induced reductions in haemorrhagic tolerance is not known. This study tested the hypothesis that fluid loss due to sweating contributes to reductions in simulated haemorrhagic tolerance in conditions of heat stress. Eight subjects (35 ± 8 years old; 77 ± 5 kg) underwent a normothermic time control and two heat stress trials (randomized). The two heat stress trials were as follows: (i) with slow intravenous infusion of lactated Ringer solution sufficient to offset sweat loss (IV trial); or (ii) without intravenous infusion (dehydration; DEH trial). Haemorrhage was simulated via progressive lower-body negative pressure (LBNP) to presyncope after core body (intestinal) temperature was raised by ~1.5 °C using a water-perfused suit or a normothermic time control period. The LBNP tolerance was quantified via a cumulative stress index. Middle cerebral artery blood velocity (transcranial Doppler) and mean blood pressure (Finometer®) were measured continuously. Relative changes in plasma volume were calculated from haematocrit and haemoglobin. Increases in core body temperature and sweat loss (~1.6% body mass deficit) were similar (P > 0.05) between heat stress trials. Slow intravenous infusion (1.2 ± 0.3 litres) prevented heat-induced reductions in plasma volume (IV trial, -0.6 ± 6.1%; and DEH trial, -6.6 ± 5.1%; P = 0.01). Intravenous infusion improved LBNP tolerance (632 ± 64 mmHg min) by ~20% when compared with the DEH trial (407 ± 117 mmHg min; P = 0.01), yet tolerance remained 44% lower in the IV trial relative to the time control normothermic trial (1138 ± 183 mmHg min; P < 0.01). These data indicate that although sweat-induced dehydration impairs simulated haemorrhagic tolerance, this impairment is secondary to the negative impact of heat stress itself.
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Affiliation(s)
- Rebekah A I Lucas
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas, TX 75231, USA
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Brothers RM, Ganio MS, Lucas RAI, Crandall CG. Tolerance to a hemorrhagic challenge during heat stress is improved with inspiratory resistance breathing. FASEB J 2012. [DOI: 10.1096/fasebj.26.1_supplement.1080.9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- R. Matthew Brothers
- Institute for Exercise and Environmental MedicineTexas Health Presbyterian Hospital DallasDallasTX
- University of Texas at AustinAustinTX
| | - Matthew S. Ganio
- Institute for Exercise and Environmental MedicineTexas Health Presbyterian Hospital DallasDallasTX
- University of ArkansasFayettevilleAR
| | - Rebekah A. I. Lucas
- Institute for Exercise and Environmental MedicineTexas Health Presbyterian Hospital DallasDallasTX
- University of Texas Southwestern Medical CenterDallasTX
| | - Craig G Crandall
- Institute for Exercise and Environmental MedicineTexas Health Presbyterian Hospital DallasDallasTX
- University of Texas Southwestern Medical CenterDallasTX
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Gagnon D, Ganio MS, Lucas RAI, Pearson J, Crandall CG, Kenny GP. Modified iodine-paper technique for the standardized determination of sweat gland activation. J Appl Physiol (1985) 2012; 112:1419-25. [PMID: 22323650 DOI: 10.1152/japplphysiol.01508.2011] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Quantifying sweat gland activation provides important information when explaining differences in sweat rate between populations and physiological conditions. However, no standard technique has been proposed to measure sweat gland activation, while the reliability of sweat gland activation measurements is unknown. We examined the interrater and internal reliability of the modified-iodine paper technique, as well as compared computer-aided analysis to manual counts of sweat gland activation. Iodine-impregnated paper was pressed against the skin of 35 participants in whom sweating was elicited by exercise in the heat or infusion of methylcholine. The number of active glands was subsequently determined by computer-aided analysis. In total, 382 measurements were used to evaluate: 1) agreement between computer analysis and manual counts; 2) the interrater reliability of computer analysis between independent investigators; and 3) the internal reliability of sweat gland activation measurements between duplicate samples. The number of glands identified with computer analysis did not differ from manual counts (68 ± 29 vs. 72 ± 24 glands/cm(2); P = 0.27). These measures were highly correlated (r = 0.77) with a mean bias ± limits of agreement of -4 ± 38 glands/cm(2). When comparing computer analysis measures between investigators, values were highly correlated (r = 0.95; P < 0.001) and the mean bias ± limits of agreement was 4 ± 18 glands/cm(2). Finally, duplicate measures of sweat gland activation were highly correlated (r = 0.88; P < 0.001) with a mean bias ± limits of agreement of 3 ± 29 glands/cm(2). These results favor the use of the modified-iodine paper technique with computer-aided analysis as a standard technique to reliably evaluate the number of active sweat glands.
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Affiliation(s)
- Daniel Gagnon
- Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ontario, Canada
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Ganio MS, Brothers RM, Lucas RAI, Hastings JL, Crandall CG. Validity of auscultatory and Penaz blood pressure measurements during profound heat stress alone and with an orthostatic challenge. Am J Physiol Regul Integr Comp Physiol 2011; 301:R1510-6. [PMID: 21832209 DOI: 10.1152/ajpregu.00247.2011] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Despite frequent reporting of blood pressure (BP) during profound passive heat stress, both with and without a hypotensive challenge, the method by which BP is measured often varies between laboratories. It is unknown whether auscultatory and finger BP measures accurately reflect intra-arterial BP during dynamic changes in cardiac output and peripheral resistance associated with the aforementioned conditions. The purpose of this investigation was to test the hypothesis that auscultatory BP measured at the brachial artery, and finger BP measured by the Penaz method, are valid measures of intra-arterial BP during a passive heat stress and a heat-stressed orthostatic challenge, via lower body negative pressure (LBNP). Absolute (specific aim 1) and the change in (specific aim 2) systolic (SBP), diastolic (DBP), and mean BPs (MBP) were compared at normothermia, after a core temperature increase of 1.47 ± 0.09°C, and during subsequent LBNP. Heat stress did not change auscultatory SBP (6 ± 11 mmHg; P = 0.16), but Penaz SBP (-22 ± 16 mmHg; P < 0.001) and intra-arterial SBP (-11 ± 13 mmHg P = 0.017) decreased. In contrast, DBP and MBP did not differ between methods throughout heat stress. Compared with BP before LBNP, the magnitude of the reduction in BP with all three methods was similar throughout LBNP (P > 0.05). In conclusion, auscultatory SBP and Penaz SBP failed to track the decrease in intra-arterial SBP that occurred during the profound heat stress, while decreases in arterial BP during an orthostatic challenge are comparable between methodologies.
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Affiliation(s)
- Matthew S Ganio
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, and University of Texas Southwestern Medical Center, Dallas, Texas, USA
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Brothers RM, Lucas RAI, Armstrong K, Hubing KA, Crandall CG, Zhang R. Cerebral Vasomotor Reactivity: Steady-State vs. Transient Changes in Carbon Dioxide Partial Pressure. Med Sci Sports Exerc 2011. [DOI: 10.1249/01.mss.0000402058.59566.eb] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Lucas RAI, Ganio MS, Brothers RM, Pearson J, Crandall CG. Cerebral Blood Flow Velocity at Hyperthermic Presyncope. Med Sci Sports Exerc 2011. [DOI: 10.1249/01.mss.0000401886.46697.da] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Lucas RAI, Ganio MS, Pearson J, Crandall CG. Dehydration during whole‐body heat stress contributes to subsequent reductions in lower‐body negative pressure (LBNP) tolerance. FASEB J 2011. [DOI: 10.1096/fasebj.25.1_supplement.1053.6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Rebekah A. I. Lucas
- Internal MedicineUniversity of Texas Southwestern Medical CenterDallasTX
- Institute for Exercise and Environmental MedicineTexas Health Presbyterian HospitalDallasTX
| | - Matthew S. Ganio
- Internal MedicineUniversity of Texas Southwestern Medical CenterDallasTX
- Institute for Exercise and Environmental MedicineTexas Health Presbyterian HospitalDallasTX
| | - James Pearson
- Internal MedicineUniversity of Texas Southwestern Medical CenterDallasTX
- Institute for Exercise and Environmental MedicineTexas Health Presbyterian HospitalDallasTX
| | - Craig G. Crandall
- Internal MedicineUniversity of Texas Southwestern Medical CenterDallasTX
- Institute for Exercise and Environmental MedicineTexas Health Presbyterian HospitalDallasTX
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Lucas SJE, Burgess KR, Thomas KN, Donnelly J, Peebles KC, Lucas RAI, Fan JL, Cotter JD, Basnyat R, Ainslie PN. Alterations in cerebral blood flow and cerebrovascular reactivity during 14 days at 5050 m. J Physiol 2010; 589:741-53. [PMID: 21041534 PMCID: PMC3052440 DOI: 10.1113/jphysiol.2010.192534] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Upon ascent to high altitude, cerebral blood flow (CBF) rises substantially before returning to sea-level values. The underlying mechanisms for these changes are unclear. We examined three hypotheses: (1) the balance of arterial blood gases upon arrival at and across 2 weeks of living at 5050 m will closely relate to changes in CBF; (2) CBF reactivity to steady-state changes in CO2 will be reduced following this 2 week acclimatisation period, and (3) reductions in CBF reactivity to CO2 will be reflected in an augmented ventilatory sensitivity to CO2. We measured arterial blood gases, middle cerebral artery blood flow velocity (MCAv, index of CBF) and ventilation () at rest and during steady-state hyperoxic hypercapnia (7% CO2) and voluntary hyperventilation (hypocapnia) at sea level and then again following 2–4, 7–9 and 12–15 days of living at 5050 m. Upon arrival at high altitude, resting MCAv was elevated (up 31 ± 31%; P < 0.01; vs. sea level), but returned to sea-level values within 7–9 days. Elevations in MCAv were strongly correlated (R2= 0.40) with the change in ratio (i.e. the collective tendency of arterial blood gases to cause CBF vasodilatation or constriction). Upon initial arrival and after 2 weeks at high altitude, cerebrovascular reactivity to hypercapnia was reduced (P < 0.05), whereas hypocapnic reactivity was enhanced (P < 0.05 vs. sea level). Ventilatory response to hypercapnia was elevated at days 2–4 (P < 0.05 vs. sea level, 4.01 ± 2.98 vs. 2.09 ± 1.32 l min−1 mmHg−1). These findings indicate that: (1) the balance of arterial blood gases accounts for a large part of the observed variability (∼40%) leading to changes in CBF at high altitude; (2) cerebrovascular reactivity to hypercapnia and hypocapnia is differentially affected by high-altitude exposure and remains distorted during partial acclimatisation, and (3) alterations in cerebrovascular reactivity to CO2 may also affect ventilatory sensitivity.
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Affiliation(s)
- Samuel J E Lucas
- Department of Physiology, University of Otago, Dunedin, New Zealand.
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Wilson LC, Cotter JD, Fan JL, Lucas RAI, Thomas KN, Ainslie PN. Cerebrovascular reactivity and dynamic autoregulation in tetraplegia. Am J Physiol Regul Integr Comp Physiol 2010; 298:R1035-42. [PMID: 20089710 DOI: 10.1152/ajpregu.00815.2009] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Humans with spinal cord injury have impaired cardiovascular function proportional to the level and completeness of the lesion. The effect on cerebrovascular function is unclear, especially for high-level lesions. The purpose of this study was to evaluate the integrity of dynamic cerebral autoregulation (CA) and the cerebrovascular reactivity in chronic tetraplegia (Tetra). After baseline, steady-state hypercapnia (5% CO(2)) and hypocapnia (controlled hyperventilation) were used to assess cerebrovascular reactivity in 6 men with Tetra (C5-C7 lesion) and 14 men without [able-bodied (AB)]. Middle cerebral artery blood flow velocity (MCAv), cerebral oxygenation, arterial blood pressure (BP), heart rate (HR), cardiac output (Q; model flow), partial pressure of end-tidal CO(2) (Pet(CO(2))), and plasma catecholamines were measured. Dynamic CA was assessed by transfer function analysis of spontaneous fluctuations in BP and MCAv. MCAv pulsatility index (MCAv PI) was calculated as (MCAv(systolic) - MCAv(diastolic))/MCAv(mean) and standardized by dividing by mean arterial pressure (MAP). Resting BP, total peripheral resistance, and catecholamines were lower in Tetra (P < 0.05), and standardized MCAv PI was approximately 36% higher in Tetra (P = 0.003). Resting MCAv, cerebral oxygenation, HR, and Pet(CO(2)) were similar between groups (P > 0.05). Although phase and transfer function gain relationships in dynamic CA were maintained with Tetra (P > 0.05), coherence in the very low-frequency range (0.02-0.07 Hz) was approximately 21% lower in Tetra (P = 0.006). Full (hypo- and hypercapnic) cerebrovascular reactivity to CO(2) was unchanged with Tetra (P > 0.05). During hypercapnia, standardized MCAv PI reactivity was enhanced by approximately 78% in Tetra (P = 0.016). Despite impaired cardiovascular function, chronic Tetra involves subtle changes in dynamic CA and cerebrovascular reactivity to CO(2). Changes are evident in coherence at baseline and MCAv PI during baseline and hypercapnic states in chronic Tetra, which may be indicative of cerebrovascular adaptation.
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Affiliation(s)
- Luke C Wilson
- Department of Physiology, University of British Columbia Okanagan, Kelowna, BC V1X, Canada
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