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Deshayes TA, Sodabi DGA, Dubord M, Gagnon D. Shifting focus: Time to look beyond the classic physiological adaptations associated with human heat acclimation. Exp Physiol 2024; 109:335-349. [PMID: 37885125 PMCID: PMC10988689 DOI: 10.1113/ep091207] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2023] [Accepted: 10/12/2023] [Indexed: 10/28/2023]
Abstract
Planet Earth is warming at an unprecedented rate and our future is now assured to be shaped by the consequences of more frequent hot days and extreme heat. Humans will need to adapt both behaviorally and physiologically to thrive in a hotter climate. From a physiological perspective, countless studies have shown that human heat acclimation increases thermoeffector output (i.e., sweating and skin blood flow) and lowers cardiovascular strain (i.e., heart rate) during heat stress. However, the mechanisms mediating these adaptations remain understudied. Furthermore, several possible benefits of heat acclimation for other systems and functions involved in maintaining health and performance during heat stress remain to be elucidated. This review summarizes recent advances in human heat acclimation, with emphasis on recent studies that (1) advanced our understanding of the mechanisms mediating improved thermoeffector output and (2) investigated adaptations that go beyond those classically associated with heat acclimation. We highlight that these studies have contributed to a better understanding of the integrated physiological responses underlying human heat acclimation while leaving key unanswered questions that will need to be addressed in the future.
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Affiliation(s)
- Thomas A. Deshayes
- Montreal Heart InstituteMontréalCanada
- School of Kinesiology and Exercise ScienceUniversité de MontréalMontréalCanada
| | - Dèwanou Gilles Arnaud Sodabi
- Montreal Heart InstituteMontréalCanada
- School of Kinesiology and Exercise ScienceUniversité de MontréalMontréalCanada
| | - Marianne Dubord
- Montreal Heart InstituteMontréalCanada
- School of Kinesiology and Exercise ScienceUniversité de MontréalMontréalCanada
| | - Daniel Gagnon
- Montreal Heart InstituteMontréalCanada
- School of Kinesiology and Exercise ScienceUniversité de MontréalMontréalCanada
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2
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Zhang J, You S, Yu L, Zhang Y, Li Z, Zhao N, Zhang B, Kang L, Sun S. The hysteresis damage of cold exposure on tissue and transcript levels in mice. J Therm Biol 2024; 120:103823. [PMID: 38442663 DOI: 10.1016/j.jtherbio.2024.103823] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Revised: 02/18/2024] [Accepted: 02/20/2024] [Indexed: 03/07/2024]
Abstract
OBJECTIVES Although cold stress-induced damage to the heart and thyroid has been reported, specific organ associations between the heart and thyroid with delayed injury mechanisms have not been investigated. In this study, we determined the damage time and transcript levels of a large number of genes in the heart and thyroid after cold exposure. Meanwhile, we analysed the relationship between heart and thyroid injury in human medical records to determine the association of delayed injury from cold exposure. METHODS Mice were exposed to cold stress and hysteresis injury. Gene changes at the transcriptional level were detected using high throughput sequencing technology. The most variable genes were verified at the protein level using Western Blotting and medical records were collected and analysed. RESULTS The damage was the most severe when the animals were allowed to recover to room temperature for 4 h after exposure to cold stress. During this process, STAT1 and ATF3 genes were acutely up-regulated. Analysis of human medical records showed the highest correlation between AST and T4 under cold stress (p = 0.0011). CONCLUSIONS Exposure to cold increases blood level of free thyroid hormone and biomarkers of myocardial injury, as well as related mRNA levels. These changes were more pronounced after return to room temperature.
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Affiliation(s)
- Jing Zhang
- Shihezi University College of Chemistry and Chemical Engineering, College of Pharmacy / Key Laboratory of Xinjiang Phytomedicine Resource and Utilization, Ministry of Education, Shihezi, 832002, Xinjiang, China; Xinjiang University of Science&Technology, School of Medicine, Korla, 841000, China
| | - Shiwan You
- Shihezi University College of Chemistry and Chemical Engineering, College of Pharmacy / Key Laboratory of Xinjiang Phytomedicine Resource and Utilization, Ministry of Education, Shihezi, 832002, Xinjiang, China
| | - Lan Yu
- Shanxi Key Laboratory of Natural Products & Chemical Biology, College of Chemistry & Pharmacy, Northwest Agriculture and Forestry University, Yangling, Shaanxi, 712100, China
| | - Yuling Zhang
- Shihezi University College of Chemistry and Chemical Engineering, College of Pharmacy / Key Laboratory of Xinjiang Phytomedicine Resource and Utilization, Ministry of Education, Shihezi, 832002, Xinjiang, China
| | - Zuoping Li
- Shihezi University College of Chemistry and Chemical Engineering, College of Pharmacy / Key Laboratory of Xinjiang Phytomedicine Resource and Utilization, Ministry of Education, Shihezi, 832002, Xinjiang, China
| | - Na Zhao
- Shihezi University College of Chemistry and Chemical Engineering, College of Pharmacy / Key Laboratory of Xinjiang Phytomedicine Resource and Utilization, Ministry of Education, Shihezi, 832002, Xinjiang, China
| | - Bo Zhang
- Key Laboratory of Medicinal and Edible Plants Resources Development of Sichuan Education Department, Sichuan Industrial Institute of Antibiotics, School of Pharmacy, Chengdu University, Chengdu, 610106, China.
| | - Lihua Kang
- Shihezi University College of Chemistry and Chemical Engineering, College of Pharmacy / Key Laboratory of Xinjiang Phytomedicine Resource and Utilization, Ministry of Education, Shihezi, 832002, Xinjiang, China.
| | - Shiguo Sun
- Shihezi University College of Chemistry and Chemical Engineering, College of Pharmacy / Key Laboratory of Xinjiang Phytomedicine Resource and Utilization, Ministry of Education, Shihezi, 832002, Xinjiang, China; Shanxi Key Laboratory of Natural Products & Chemical Biology, College of Chemistry & Pharmacy, Northwest Agriculture and Forestry University, Yangling, Shaanxi, 712100, China.
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3
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Garcia CK, Gambino BJ, Robinson GP, Rua MT, Alzahrani JM, Clanton TL. Delayed metabolic disturbances in the myocardium after exertional heat stroke: contrasting effects of exertion and thermal load. J Appl Physiol (1985) 2023; 135:1186-1198. [PMID: 37795530 PMCID: PMC10979828 DOI: 10.1152/japplphysiol.00372.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Revised: 09/05/2023] [Accepted: 09/27/2023] [Indexed: 10/06/2023] Open
Abstract
Epidemiological studies report higher risks of cardiovascular disease in humans exposed to heat stroke earlier in life. Previously, we explored mechanistic links between heat stroke and developing cardiac abnormalities using a preclinical mouse model of exertional heat stroke (EHS). Profound metabolic abnormalities developed in the ventricles of females but not males after 2 wk of recovery. Here we tested whether this lack of response in males could be attributed to the lower exercise performances or reduced thermal loads they experienced with the same running protocol. We systematically altered environmental temperature (Te) during EHS to manipulate heat exposure and exercise performance in the males. Three groups of adult C57BL/6 male mice were studied: "EHS-34" (Te = 34°C), "EHS-41" (Te = 41°C), and "EHS-39.5" (Te = 39.5°C). Mice ran until symptom limitation (unconsciousness), reaching max core temperature (Tc,max). After a 2-wk recovery, the mice were euthanized, and the ventricles were removed for untargeted metabolomics. Results were compared against age-matched nonexercise controls. The EHS-34 mice greatly elevated their exercise performance but reached lower Tc,max and lower thermal loads. The EHS-41 mice exhibited equivalent thermal loads, exercise times, and Tc,max compared with EHS-39.5. The ventricles from EHS-34 mice exhibited the greatest metabolic disturbances in the heart, characterized by shifts toward glucose metabolism, reductions in acylcarnitines, increased amino acid metabolites, elevations in antioxidants, altered TCA cycle flux, and increased xenobiotics. In conclusion, delayed metabolic disturbances following EHS in male myocardium appear to be greatly amplified by higher levels of exertion in the heat, even with lower thermal loads and max core temperatures.NEW & NOTEWORTHY Epidemiological data demonstrate greater cardiovascular risk in patients with previous heat stroke exposure. Using a preclinical mouse model of exertional heat stroke, male mice were exposed to one of three environmental temperatures (Te) during exercise. Paradoxically, after 2 wk, the mice in the lowest Te, exhibiting the largest exercise response and lowest heat load, had the greatest ventricular metabolic disturbances. Metabolic outcomes resemble developing left ventricular hypertrophy or stress-induced heart disease.
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Affiliation(s)
- Christian K Garcia
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida, United States
| | - Bryce J Gambino
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida, United States
| | - Gerard P Robinson
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida, United States
| | - Michael T Rua
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida, United States
| | - Jamal M Alzahrani
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida, United States
| | - Thomas L Clanton
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida, United States
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4
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Goswami N. Compensatory hemodynamic changes in response to central hypovolemia in humans: lower body negative pressure: updates and perspectives. J Muscle Res Cell Motil 2023; 44:89-94. [PMID: 36380185 PMCID: PMC10329599 DOI: 10.1007/s10974-022-09635-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2022] [Accepted: 10/19/2022] [Indexed: 11/16/2022]
Abstract
Central hypovolemia is accompanied by hemodynamic compensatory responses. Understanding the complex systemic compensatory responses to altered hemodynamic patterns during conditions of central hypovolemia-as induced by standing up and/or lower body negative pressure (LBNP)-in humans are important. LBNP has been widely used to understand the integrated physiological responses, which occur during sit to stand tests (orthostasis), different levels of hemorrhages (different levels of LBNP simulate different amount of blood loss) as well as a countermeasure against the cephalad fluid shifts which are seen during spaceflight. Additionally, LBNP application (used singly or together with head up tilt, HUT) is useful in understanding the physiology of orthostatic intolerance. The role seasonal variations in hormonal, autonomic and circulatory state play in LBNP-induced hemodynamic responses and LBNP tolerance as well as sex-based differences during central hypovolemia and the adaptations to exercise training have been investigated using LBNP. The data generated from LBNP studies have been useful in developing better models for prediction of orthostatic tolerance and/or for developing countermeasures. This review examines how LBNP application influences coagulatory parameters and outlines the effects of temperature changes on LBNP responses. Finally, the review outlines how LBNP can be used as innovative teaching tool and for developing research capacities and interests of medical students and students from other disciplines such as mathematics and computational biology.
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Affiliation(s)
- Nandu Goswami
- Division of Physiology, Gravitational Physiology and Medicine Research Unit, Otto Löwi Research Center of Vascular Biology, Inflammation, and Immunity, Medical University of Graz, Neue Stiftingtalstrasse 6, D-5, 8036, Graz, Austria.
- College of Medicine, Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai, United Arab Emirates.
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Kagelmann N, Janke D, Maggioni MA, Gunga HC, Riveros Rivera A, Genov M, Noppe A, Habazettl H, Bothe TL, Nordine M, Castiglioni P, Opatz O. Peripheral skin cooling during hyper-gravity: hemodynamic reactions. Front Physiol 2023; 14:1173171. [PMID: 37256071 PMCID: PMC10225582 DOI: 10.3389/fphys.2023.1173171] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2023] [Accepted: 04/27/2023] [Indexed: 06/01/2023] Open
Abstract
Introduction: Orthostatic dysregulation occurs during exposure to an increased gravitational vector and is especially common upon re-entering standard Earth gravity (1 g) after an extended period in microgravity (0 g). External peripheral skin cooling (PSC) has recently been described as a potent countermeasure against orthostatic dysregulation during heat stress and in lower body negative pressure (LBNP) studies. We therefore hypothesized that PSC may also be an effective countermeasure during hyper-gravity exposure (+Gz). Methods: To investigate this, we designed a randomized short-arm human centrifuge (SAHC) experiment ("Coolspin") to investigate whether PSC could act as a stabilizing factor in cardiovascular function during +Gz. Artificial gravity between +1 g and +4 g was generated by a SAHC. 18 healthy male volunteers completed two runs in the SAHC. PSC was applied during one of the two runs and the other run was conducted without cooling. Each run consisted of a 10-min baseline trial followed by a +Gz step protocol marked by increasing g-forces, with each step being 3 min long. The following parameters were measured: blood pressure (BP), heart rate (HR), stroke volume (SV), total peripheral resistance (TPR), cardiac output (CO). Furthermore, a cumulative stress index for each subject was calculated. Results: +Gz led to significant changes in primary as well as in secondary outcome parameters such as HR, SV, TPR, CO, and BP. However, none of the primary outcome parameters (HR, cumulative stress-index, BP) nor secondary outcome parameters (SV, TPR, CO) showed any significant differences-whether the subject was cooled or not cooled. Systolic BP did, however, tend to be higher amongst the PSC group. Conclusion: In conclusion, PSC during +Gz did not confer any significant impact on hemodynamic activity or orthostatic stability during +Gz. This may be due to lower PSC responsiveness of the test subjects, or an insufficient level of body surface area used for cooling. Further investigations are warranted in order to comprehensively pinpoint the exact degree of PSC needed to serve as a useful countermeasure system during +Gz.
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Affiliation(s)
- Niklas Kagelmann
- Charité—Universitätsmedizin Berlin, Institute of Physiology, Center for Space Medicine and Extreme Environments Berlin, Berlin, Germany
| | - David Janke
- Charité—Universitätsmedizin Berlin, Institute of Physiology, Center for Space Medicine and Extreme Environments Berlin, Berlin, Germany
| | - Martina Anna Maggioni
- Charité—Universitätsmedizin Berlin, Institute of Physiology, Center for Space Medicine and Extreme Environments Berlin, Berlin, Germany
- Department of Biomedical Sciences for Health, Università degli Studi di Milano, Milan, Italy
| | - Hanns-Christian Gunga
- Charité—Universitätsmedizin Berlin, Institute of Physiology, Center for Space Medicine and Extreme Environments Berlin, Berlin, Germany
| | - Alain Riveros Rivera
- Department of Physiological Sciences, Pontificia Universidad Javeriana, Bogotá, Colombia
| | - Magdalena Genov
- Charité—Universitätsmedizin Berlin, Institute of Physiology, Center for Space Medicine and Extreme Environments Berlin, Berlin, Germany
| | - Alexandra Noppe
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
| | - Helmut Habazettl
- Charité—Universitätsmedizin Berlin, Institute of Physiology, Center for Space Medicine and Extreme Environments Berlin, Berlin, Germany
| | - Tomas Lucca Bothe
- Charité—Universitätsmedizin Berlin, Institute of Physiology, Center for Space Medicine and Extreme Environments Berlin, Berlin, Germany
- Charité—Universitätsmedizin Berlin, Institute of Translational Physiology, Berlin, Germany
| | - Michael Nordine
- Department of Anaesthesiology, Intensive Care Medicine and Pain Therapy, University Hospital Frankfurt, Goethe University Frankfurt, Frankfurt, Germany
| | - Paolo Castiglioni
- Department of Biotechnology and Life Sciences (DBSV), University of Insubria, Varese, Italy
- IRCCS Fondazione Don Carlo Gnocchi ONLUS, Milan, Italy
| | - Oliver Opatz
- Charité—Universitätsmedizin Berlin, Institute of Physiology, Center for Space Medicine and Extreme Environments Berlin, Berlin, Germany
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6
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Roths M, Freestone AD, Rudolph TE, Michael A, Baumgard LH, Selsby JT. Environment-induced heat stress causes structural and biochemical changes in the heart. J Therm Biol 2023; 113:103492. [PMID: 37055111 DOI: 10.1016/j.jtherbio.2023.103492] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2022] [Revised: 01/27/2023] [Accepted: 01/29/2023] [Indexed: 02/07/2023]
Abstract
Prolonged exposure to heat can lead to environment-induced heat stress (EIHS), which may jeopardize human health, but the extent to which EIHS affects cardiac architecture and myocardial cell health are unknown. We hypothesized EIHS would alter cardiac structure and cause cellular dysfunction. To test this hypothesis, 3-mo old female pigs were exposed to thermoneutral (TN; 20.6 ± 0.2 °C; n = 8) or EIHS (37.4 ± 0.2 °C; n = 8) conditions for 24 h, hearts were removed and dimensions measured, and portions of the left ventricle (LV) and right ventricle (RV) were collected. Environment-induced heat stress increased rectal temperature 1.3 °C (P < 0.01), skin temperature 11 °C (P < 0.01) and respiratory rate 72 breaths per minute (P < 0.01). Heart weight and length (apex to base) were decreased by 7.6% (P = 0.04) and 8.5% (P = 0.01), respectively, by EIHS, but heart width was similar between groups. Left ventricle wall thickness was increased (22%; P = 0.02) and water content was decreased (8.6%; P < 0.01) whereas in RV, wall thickness was decreased (26%; P = 0.04) and water content was similar in EIHS compared to TN. We also discovered ventricle-specific biochemical changes such that in RV EIHS increased heat shock proteins, decreased AMPK and AKT signaling, decreased activation of mTOR (35%; P < 0.05), and increased expression of proteins that participate in autophagy. In LV, heat shock proteins, AMPK and AKT signaling, activation of mTOR, and autophagy-related proteins were largely similar between groups. Biomarkers suggest EIHS-mediated reductions in kidney function. These data demonstrate EIHS causes ventricular-dependent changes and may undermine cardiac health, energy homeostasis, and function.
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7
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Savioli G, Zanza C, Longhitano Y, Nardone A, Varesi A, Ceresa IF, Manetti AC, Volonnino G, Maiese A, La Russa R. Heat-Related Illness in Emergency and Critical Care: Recommendations for Recognition and Management with Medico-Legal Considerations. Biomedicines 2022; 10:biomedicines10102542. [PMID: 36289804 PMCID: PMC9599879 DOI: 10.3390/biomedicines10102542] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2022] [Revised: 09/22/2022] [Accepted: 10/06/2022] [Indexed: 11/30/2022] Open
Abstract
Hyperthermia is an internal body temperature increase above 40.5 °C; normally internal body temperature is kept constant through natural homeostatic mechanisms. Heat-related illnesses occur due to exposure to high environmental temperatures in conditions in which an organism is unable to maintain adequate homeostasis. This can happen, for example, when the organism is unable to dissipate heat adequately. Heat dissipation occurs through evaporation, conduction, convection, and radiation. Heat disease exhibits a continuum of signs and symptoms ranging from minor to major clinical pictures. Minor clinical pictures include cramps, syncope, edema, tetany, and exhaustion. Major clinical pictures include heatstroke and life-threatening heat stroke and typically are expressed in the presence of an extremely high body temperature. There are also some categories of people at greater risk of developing these diseases, due to exposure in particular geographic areas (e.g., hot humid environments), to unchangeable predisposing conditions (e.g., advanced age, young age (i.e., children), diabetes, skin disease with reduced sweating), to modifiable risk factors (e.g., alcoholism, excessive exercise, infections), to partially modifiable risk factors (obesity), to certain types of professional activity (e.g., athletes, military personnel, and outdoor laborers) or to the effects of drug treatment (e.g., beta-blockers, anticholinergics, diuretics). Heat-related illness is largely preventable.
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Affiliation(s)
- Gabriele Savioli
- Emergency Department, IRCCS Policlinico San Matteo, 27100 Pavia, Italy
- Doctoral Program Experimental Medicine, Department of Clinical-Surgical, Diagnostic and Pediatric Sciences, University of Pavia, 27100 Pavia, Italy
| | - Christian Zanza
- Foundation “Ospedale Alba-Bra”, Department of Emergency Medicine, Anesthesia and Critical Care Medicine, Michele and Pietro Ferrero Hospital, 12060 Verduno, Italy
- Correspondence:
| | - Yaroslava Longhitano
- Foundation “Ospedale Alba-Bra”, Department of Emergency Medicine, Anesthesia and Critical Care Medicine, Michele and Pietro Ferrero Hospital, 12060 Verduno, Italy
| | - Alba Nardone
- Department of Internal Medicine, Università degli Studi of Pavia, 27100 Pavia, Italy
| | - Angelica Varesi
- Department of Internal Medicine, Università degli Studi of Pavia, 27100 Pavia, Italy
| | | | - Alice Chiara Manetti
- Department of Surgical, Medical and Molecular Pathology and Critical Care Medicine, Institute of Legal Medicine, University of Pisa, 56126 Pisa, Italy
| | - Gianpietro Volonnino
- Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Sapienza University, 00185 Rome, Italy
| | - Aniello Maiese
- Department of Surgical, Medical and Molecular Pathology and Critical Care Medicine, Institute of Legal Medicine, University of Pisa, 56126 Pisa, Italy
| | - Raffaele La Russa
- Department of Clinical and Experimental Medicine, University of Foggia, 71122 Foggia, Italy
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Fischer M, Moralez G, Sarma S, MacNamara JP, Cramer MN, Huang M, Romero SA, Hieda M, Shibasaki M, Ogoh S, Crandall CG. Altered cardiac β1 responsiveness in hyperthermic older adults. Am J Physiol Regul Integr Comp Physiol 2022; 323:R581-R588. [PMID: 36094450 PMCID: PMC9602700 DOI: 10.1152/ajpregu.00040.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Revised: 08/30/2022] [Accepted: 09/06/2022] [Indexed: 11/22/2022]
Abstract
Compared with younger adults, passive heating induced increases in cardiac output are attenuated by ∼50% in older adults. This attenuated response may be associated with older individuals' inability to maintain stroke volume through ionotropic mechanisms and/or through altered chronotropic mechanisms. The purpose of this study was to identify the interactive effect of age and hyperthermia on cardiac responsiveness to dobutamine-induced cardiac stimulation. Eleven young (26 ± 4 yr) and 8 older (68 ± 5 yr) participants underwent a normothermic and a hyperthermic (baseline core temperature +1.2°C) trial on the same day. In both thermal conditions, after baseline measurements, intravenous dobutamine was administered for 12 min at 5 µg/kg/min, followed by 12 min at 15 µg/kg/min. Primary measurements included echocardiography-based assessments of cardiac function, gastrointestinal and skin temperatures, heart rate, and mean arterial pressure. Heart rate responses to dobutamine were similar between groups in both thermal conditions (P > 0.05). The peak systolic mitral annular velocity (S'), i.e., an index of left ventricular longitudinal systolic function, was similar between groups for both thermal conditions at baseline. While normothermic, the increase in S' between groups was similar with dobutamine administration. However, while hyperthermic, the increase in S' was attenuated in the older participants with dobutamine (P < 0.001). Healthy, older individuals show attenuated inotropic, but maintained chronotropic responsiveness to dobutamine administration during hyperthermia. These data suggest that older individuals have a reduced capacity to increase cardiomyocyte contractility, estimated by changes in S', via β1-adrenergic mechanisms while hyperthermic.
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Affiliation(s)
- Mads Fischer
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
- Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark
| | - Gilbert Moralez
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
- Applied Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Satyam Sarma
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - James P MacNamara
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - Matthew N Cramer
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - Mu Huang
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
- Applied Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Steven A Romero
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
- Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, Texas
| | - Michinari Hieda
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
- School of Medicine, Kyushu University, Fukuoka, Japan
| | - Manabu Shibasaki
- Department of Environmental Health, Nara Women's University, Nara, Japan
| | - Shigehiko Ogoh
- Department of Biomedical Engineering, Toyo University, Saitama, Japan
| | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
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Chou TH, Coyle EF. Cardiovascular responses to hot skin at rest and during exercise. Temperature (Austin) 2022; 10:326-357. [PMID: 37554384 PMCID: PMC10405766 DOI: 10.1080/23328940.2022.2109931] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Revised: 07/25/2022] [Accepted: 07/30/2022] [Indexed: 10/15/2022] Open
Abstract
Integrative cardiovascular responses to heat stress during endurance exercise depend on various variables, such as thermal stress and exercise intensity. This review addresses how increases in skin temperature alter and challenge the integrative cardiovascular system during upright submaximal endurance exercise, especially when skin is hot (i.e. >38°C). Current evidence suggests that exercise intensity plays a significant role in cardiovascular responses to hot skin during exercise. At rest and during mild intensity exercise, hot skin increases skin blood flow and abolishes cutaneous venous tone, which causes blood pooling in the skin while having little impact on stroke volume and thus cardiac output is increased with an increase in heart rate. When the heart rate is at relatively low levels, small increases in heart rate, skin blood flow, and cutaneous venous volume do not compromise stroke volume, so cardiac output can increase to fulfill the demands for maintaining blood pressure, heat dissipation, and the exercising muscle. On the contrary, during more intense exercise, hot skin does not abolish exercise-induced cutaneous venoconstriction possibly due to high sympathetic nerve activities; thus, it does not cause blood pooling in the skin. However, hot skin reduces stroke volume, which is associated with a decrease in ventricular filling time caused by an increase in heart rate. When the heart rate is high during moderate or intense exercise, even a slight reduction in ventricular filling time lowers stroke volume. Cardiac output is therefore not elevated when skin is hot during moderate intensity exercise.
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Affiliation(s)
- Ting-Heng Chou
- Center for Regenerative Medicine, The Research Institute at Nationwide Children’s Hospital, Columbus, OH, USA
| | - Edward F. Coyle
- Department of Kinesiology and Health Education, The University of Texas at Austin, Texas, Tx, USA
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10
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Extreme Heat and Cardiovascular Health: What a Cardiovascular Health Professional Should Know. Can J Cardiol 2021; 37:1828-1836. [PMID: 34802857 DOI: 10.1016/j.cjca.2021.08.008] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2021] [Revised: 07/23/2021] [Accepted: 08/09/2021] [Indexed: 01/22/2023] Open
Abstract
As global temperatures continue to rise, extreme heat events are becoming more frequent and intense. Extreme heat affects cardiovascular health as it is associated with a greater risk of adverse cardiovascular events, especially for adults with preexisting cardiovascular diseases. Nonetheless, the pathophysiology underlying the association between extreme heat and cardiovascular risk remains understudied. Furthermore, specific recommendations to mitigate the effects of extreme heat on cardiovascular health remain limited to guide clinical practice within the context of a warming climate. The overall objective of this review article is to raise awareness that extreme heat poses a risk for cardiovascular health. Specifically, the review discusses why cardiovascular healthcare professionals should care about extreme heat, how extreme heat affects cardiovascular health, and recommendations to minimise the cardiovascular consequences of extreme heat. Future research directions are also provided to further our understating of the cardiovascular health consequences of extreme heat. A better awareness and understanding of the cardiovascular consequences of extreme heat will help cardiovascular health professionals assess the risk and optimise the care of their patients exposed to an increasingly warm climate.
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11
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Rathod SB, Sorte SR, Patel S. The Effect of High Temperature on Cardiovascular Autonomic Function Tests in Steel Plant Furnace Worker. Indian J Occup Environ Med 2021; 25:67-71. [PMID: 34421240 PMCID: PMC8341409 DOI: 10.4103/ijoem.ijoem_193_20] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Revised: 06/20/2020] [Accepted: 07/28/2020] [Indexed: 11/07/2022] Open
Abstract
Background: The high temperature in the working environment could be one of the risk factors for cardiovascular diseases in steel plant workers. The excessive high temperature at the working place leads to altered autonomic activity and is related to more cardiovascular risk. Aims and Objectives: The effect of high temperature on cardiovascular autonomic function tests in steel plant furnace worker. Material and Method: This was a case-control study for which 50 steel plant furnace workers and 50 controls were selected. The cardiovascular sympathetic function status in worker and control were analyzed by three tests: (i) Blood pressure (BP) response to sustained isometric handgrip test, (ii) BP response to the cold pressor test, and (iii) BP response to standing from a supine position (orthostasis). Statistical analysis was done by using an independent t-test. Results: Diastolic BP (DBP) response to sustained isometric handgrip and systolic BP (SBP) and DBP response to the cold pressor test showed that the increase BP in workers were more than controls but the difference was not statistically significant (P > 0.05). SBP response to standing from the supine position showed statistically significant (P < 0.001) greater fall in steel plant workers. Conclusion: The sympathetic autonomic dysfunction was seen in steel furnace workers in response to environmental stressor–excessive heat.
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Affiliation(s)
- Sachin B Rathod
- Department of Physiology, Shri Shankaracharya Institute of Medical Sciences, Bhilai, Chattishgarh, India
| | - Smita R Sorte
- Department of Physiology, AIIMS, Nagpur, Maharashtra, India
| | - Sandeep Patel
- Shri Shankaracharya Institute of Medical Sciences, Bhilai, Chattishgarh, India
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12
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Brunt VE, Minson CT. Heat therapy: mechanistic underpinnings and applications to cardiovascular health. J Appl Physiol (1985) 2021; 130:1684-1704. [PMID: 33792402 DOI: 10.1152/japplphysiol.00141.2020] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Cardiovascular diseases (CVD) are the leading cause of death worldwide, and novel therapies are drastically needed to prevent or delay the onset of CVD to reduce the societal and healthcare burdens associated with these chronic diseases. One such therapy is "heat therapy," or chronic, repeated use of hot baths or saunas. Although using heat exposure to improve health is not a new concept, it has received renewed attention in recent years as a growing number of studies have demonstrated robust and widespread beneficial effects of heat therapy on cardiovascular health. Here, we review the existing literature, with particular focus on the molecular mechanisms that underscore the cardiovascular benefits of this practice.
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Affiliation(s)
- Vienna E Brunt
- Department of Integrative Physiology, University of Colorado Boulder, Boulder, Colorado.,Department of Human Physiology, University of Oregon, Eugene, Oregon
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13
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Okamoto LE, Celedonio JE, Smith EC, Gamboa A, Shibao CA, Diedrich A, Paranjape SY, Black BK, Muldowney JAS, Peltier AC, Habermann R, Crandall CG, Biaggioni I. Local Passive Heat for the Treatment of Hypertension in Autonomic Failure. J Am Heart Assoc 2021; 10:e018979. [PMID: 33739123 PMCID: PMC8174330 DOI: 10.1161/jaha.120.018979] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Background Supine hypertension affects a majority of patients with autonomic failure; it is associated with end‐organ damage and can worsen daytime orthostatic hypotension by inducing pressure diuresis and volume loss during the night. Because sympathetic activation prevents blood pressure (BP) from falling in healthy subjects exposed to heat, we hypothesized that passive heat had a BP‐lowering effect in patients with autonomic failure and could be used to treat their supine hypertension. Methods and Results In Protocol 1 (n=22), the acute effects of local heat (40–42°C applied with a heating pad placed over the abdomen for 2 hours) versus sham control were assessed in a randomized crossover fashion. Heat acutely decreased systolic BP by −19±4 mm Hg (versus 3±4 with sham, P<0.001) owing to decreases in stroke volume (−18±5% versus −4±4%, P=0.013 ) and cardiac output (−15±5% versus −2±4%, P=0.013). In Protocol 2 (proof‐of‐concept overnight study; n=12), we compared the effects of local heat (38°C applied with a water‐perfused heating pad placed under the torso from 10 pm to 6 am) versus placebo pill. Heat decreased nighttime systolic BP (maximal change −28±6 versus −2±6 mm Hg, P<0.001). BP returned to baseline by 8 am. The nocturnal systolic BP decrease correlated with a decrease in urinary volume (r=0.57, P=0.072) and an improvement in the morning upright systolic BP (r=−0.76, P=0.007). Conclusions Local heat therapy effectively lowered overnight BP in patients with autonomic failure and supine hypertension and offers a novel approach to treat this condition. Future studies are needed to assess the long‐term safety and efficacy in improving nighttime fluid loss and daytime orthostatic hypotension. Registration URL: https://www.clinicaltrials.gov; Unique identifiers: NCT02417415 and NCT03042988.
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Affiliation(s)
- Luis E Okamoto
- Vanderbilt Autonomic Dysfunction Center Vanderbilt University Medical Center Nashville TN.,Division of Clinical Pharmacology Vanderbilt University Medical Center Nashville TN.,Department of Medicine Vanderbilt University Medical Center Nashville TN
| | - Jorge E Celedonio
- Vanderbilt Autonomic Dysfunction Center Vanderbilt University Medical Center Nashville TN.,Division of Clinical Pharmacology Vanderbilt University Medical Center Nashville TN.,Department of Medicine Vanderbilt University Medical Center Nashville TN
| | - Emily C Smith
- Vanderbilt Autonomic Dysfunction Center Vanderbilt University Medical Center Nashville TN.,Division of Clinical Pharmacology Vanderbilt University Medical Center Nashville TN.,Department of Medicine Vanderbilt University Medical Center Nashville TN
| | - Alfredo Gamboa
- Vanderbilt Autonomic Dysfunction Center Vanderbilt University Medical Center Nashville TN.,Division of Clinical Pharmacology Vanderbilt University Medical Center Nashville TN.,Department of Medicine Vanderbilt University Medical Center Nashville TN
| | - Cyndya A Shibao
- Vanderbilt Autonomic Dysfunction Center Vanderbilt University Medical Center Nashville TN.,Division of Clinical Pharmacology Vanderbilt University Medical Center Nashville TN.,Department of Medicine Vanderbilt University Medical Center Nashville TN
| | - André Diedrich
- Vanderbilt Autonomic Dysfunction Center Vanderbilt University Medical Center Nashville TN.,Division of Clinical Pharmacology Vanderbilt University Medical Center Nashville TN.,Department of Medicine Vanderbilt University Medical Center Nashville TN.,Department of Biomedical Engineering Vanderbilt University Medical Center Nashville TN
| | - Sachin Y Paranjape
- Vanderbilt Autonomic Dysfunction Center Vanderbilt University Medical Center Nashville TN.,Division of Clinical Pharmacology Vanderbilt University Medical Center Nashville TN.,Department of Medicine Vanderbilt University Medical Center Nashville TN
| | - Bonnie K Black
- Vanderbilt Autonomic Dysfunction Center Vanderbilt University Medical Center Nashville TN.,Division of Clinical Pharmacology Vanderbilt University Medical Center Nashville TN.,Department of Medicine Vanderbilt University Medical Center Nashville TN
| | - James A S Muldowney
- Vanderbilt Autonomic Dysfunction Center Vanderbilt University Medical Center Nashville TN.,Division of Clinical Pharmacology Vanderbilt University Medical Center Nashville TN.,Division of Cardiology Vanderbilt University Medical Center Nashville TN.,Department of Medicine Vanderbilt University Medical Center Nashville TN
| | - Amanda C Peltier
- Vanderbilt Autonomic Dysfunction Center Vanderbilt University Medical Center Nashville TN.,Division of Clinical Pharmacology Vanderbilt University Medical Center Nashville TN.,Department of Neurology Vanderbilt University Medical Center Nashville TN
| | - Ralf Habermann
- Vanderbilt Autonomic Dysfunction Center Vanderbilt University Medical Center Nashville TN.,Division of Clinical Pharmacology Vanderbilt University Medical Center Nashville TN.,Division of Geriatrics Vanderbilt University Medical Center Nashville TN.,Department of Medicine Vanderbilt University Medical Center Nashville TN
| | - Craig G Crandall
- Institute for Exercise and Environmental Medicine Texas Health Presbyterian Hospital and UT Southwestern Medical Center Dallas TX
| | - Italo Biaggioni
- Vanderbilt Autonomic Dysfunction Center Vanderbilt University Medical Center Nashville TN.,Division of Clinical Pharmacology Vanderbilt University Medical Center Nashville TN.,Department of Medicine Vanderbilt University Medical Center Nashville TN.,Department of Pharmacology Vanderbilt University Medical Center Nashville TN
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14
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Convertino VA, Koons NJ, Suresh MR. Physiology of Human Hemorrhage and Compensation. Compr Physiol 2021; 11:1531-1574. [PMID: 33577122 DOI: 10.1002/cphy.c200016] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Hemorrhage is a leading cause of death following traumatic injuries in the United States. Much of the previous work in assessing the physiology and pathophysiology underlying blood loss has focused on descriptive measures of hemodynamic responses such as blood pressure, cardiac output, stroke volume, heart rate, and vascular resistance as indicators of changes in organ perfusion. More recent work has shifted the focus toward understanding mechanisms of compensation for reduced systemic delivery and cellular utilization of oxygen as a more comprehensive approach to understanding the complex physiologic changes that occur following and during blood loss. In this article, we begin with applying dimensional analysis for comparison of animal models, and progress to descriptions of various physiological consequences of hemorrhage. We then introduce the complementary side of compensation by detailing the complexity and integration of various compensatory mechanisms that are activated from the initiation of hemorrhage and serve to maintain adequate vital organ perfusion and hemodynamic stability in the scenario of reduced systemic delivery of oxygen until the onset of hemodynamic decompensation. New data are introduced that challenge legacy concepts related to mechanisms that underlie baroreflex functions and provide novel insights into the measurement of the integrated response of compensation to central hypovolemia known as the compensatory reserve. The impact of demographic and environmental factors on tolerance to hemorrhage is also reviewed. Finally, we describe how understanding the physiology of compensation can be translated to applications for early assessment of the clinical status and accurate triage of hypovolemic and hypotensive patients. © 2021 American Physiological Society. Compr Physiol 11:1531-1574, 2021.
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Affiliation(s)
- Victor A Convertino
- Battlefield Healthy & Trauma Center for Human Integrative Physiology, United States Army Institute of Surgical Research, JBSA San Antonio, Texas, USA
| | - Natalie J Koons
- Battlefield Healthy & Trauma Center for Human Integrative Physiology, United States Army Institute of Surgical Research, JBSA San Antonio, Texas, USA
| | - Mithun R Suresh
- Battlefield Healthy & Trauma Center for Human Integrative Physiology, United States Army Institute of Surgical Research, JBSA San Antonio, Texas, USA
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15
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Gravel H, Chaseling GK, Barry H, Debray A, Gagnon D. Cardiovascular control during heat stress in older adults: time for an update. Am J Physiol Heart Circ Physiol 2020; 320:H411-H416. [PMID: 33275528 DOI: 10.1152/ajpheart.00536.2020] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It is generally accepted that older adults display an impaired cardiovascular response to heat stress, and it has been suggested that this impaired response contributes to their increased risk of mortality during extreme heat events. Seminal studies have shown that cutaneous vasodilation, the redistribution of blood flow from visceral organs, and the increase in cardiac output are blunted in older adults during passive heating. The blunted rise of cardiac output was initially attributed to an inability to maintain stroke volume, suggesting that cardiac systolic and/or diastolic function does not adequately respond to the constraints of heat stress in older adults. Recent studies evaluated potential mechanisms underlying these seminal findings and their results challenge some of these initial observations. Notably, stroke volume is maintained during heat exposure in older adults and studies have provided evidence for preserved cardiac systolic and diastolic functions in this population. Nonetheless, a blunted increase in cardiac output during heat exposure remains a consistent observation in older adults, although it is now attributed to a blunted increase in heart rate. Recent studies have also evaluated the possibility that the attenuated capacity of aged skin to vasodilate contributes to a blunted increase in cardiac output during heat stress. The objective of this Mini-Review is to highlight these recent advances and challenge the long-standing view that the control of stroke volume during heat exposure is compromised in older adults. By doing so, our intent is to stimulate future studies to evaluate several unanswered questions in this area of research.
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Affiliation(s)
- Hugo Gravel
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Research Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Department of Pharmacology and Physiology, Université de Montréal, Montreal, Quebec, Canada
| | - Georgia K Chaseling
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Research Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Department of Pharmacology and Physiology, Université de Montréal, Montreal, Quebec, Canada
| | - Hadiatou Barry
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Research Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Department of Pharmacology and Physiology, Université de Montréal, Montreal, Quebec, Canada
| | - Amélie Debray
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Research Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Department of Medicine, Université de Montréal, Montreal, Quebec, Canada
| | - Daniel Gagnon
- Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Research Centre, Montreal Heart Institute, Montreal, Quebec, Canada.,Department of Pharmacology and Physiology, Université de Montréal, Montreal, Quebec, Canada.,School of Kinesiology and Exercise Science, Université de Montréal, Montreal, Quebec, Canada
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16
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Trachsel LD, Barry H, Gravel H, Behzadi P, Henri C, Gagnon D. Cardiac function during heat stress: impact of short-term passive heat acclimation. Am J Physiol Heart Circ Physiol 2020; 319:H753-H764. [DOI: 10.1152/ajpheart.00407.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A lower heart rate during heat exposure is a classic marker of heat acclimation (HA). It remains unknown if improved cardiac function contributes to this response. A 7-day passive HA protocol did not alter cardiac systolic function during passive heating, whereas it improved some indexes of diastolic function in young adults. Nonetheless, heart rate during heating was unaffected by HA. These results suggest that passive HA induces limited adaptations in cardiac function during passive heating.
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Affiliation(s)
- Lukas D. Trachsel
- Cardiovascular Prevention and Rehabilitation Center, Montreal Heart Institute, Montreal, Canada
- Department of Medicine, Université de Montréal, Montreal, Canada
- University Clinic for Cardiology, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland
| | - Hadiatou Barry
- Cardiovascular Prevention and Rehabilitation Center, Montreal Heart Institute, Montreal, Canada
- Department of Pharmacology and Physiology, Université de Montréal, Montreal, Canada
| | - Hugo Gravel
- Cardiovascular Prevention and Rehabilitation Center, Montreal Heart Institute, Montreal, Canada
- Department of Pharmacology and Physiology, Université de Montréal, Montreal, Canada
| | - Parya Behzadi
- Cardiovascular Prevention and Rehabilitation Center, Montreal Heart Institute, Montreal, Canada
- Department of Pharmacology and Physiology, Université de Montréal, Montreal, Canada
| | - Christine Henri
- Department of Medicine, Université de Montréal, Montreal, Canada
- Research Centre, Montreal Heart Institute, Montreal, Canada
| | - Daniel Gagnon
- Cardiovascular Prevention and Rehabilitation Center, Montreal Heart Institute, Montreal, Canada
- Department of Pharmacology and Physiology, Université de Montréal, Montreal, Canada
- Research Centre, Montreal Heart Institute, Montreal, Canada
- School of Human Kinetics and Exercise Science, Université de Montréal, Montreal, Canada
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17
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Kuzmenko NV, Pliss MG, Galagudza MM, Tsyrlin VA. Effects of Hyper- and Hypothermia on Hemodynamic Parameters in People of Different Age Groups: Meta-Analysis. ADVANCES IN GERONTOLOGY 2020. [DOI: 10.1134/s2079057020020095] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
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18
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Abstract
People undertaking prolonged vigorous exercise experience substantial bodily fluid losses due to thermoregulatory sweating. If these fluid losses are not replaced, endurance capacity may be impaired in association with a myriad of alterations in physiological function, including hyperthermia, hyperventilation, cardiovascular strain with reductions in brain, skeletal muscle and skin blood perfusion, greater reliance on muscle glycogen and cellular metabolism, alterations in neural activity and, in some conditions, compromised muscle metabolism and aerobic capacity. The physiological strain accompanying progressive exercise-induced dehydration to a level of ~ 4% of body mass loss can be attenuated or even prevented by: (1) ingesting fluids during exercise, (2) exercising in cold environments, and/or (3) working at intensities that require a small fraction of the overall body functional capacity. The impact of dehydration upon physiological function therefore depends on the functional demand evoked by exercise and environmental stress, as cardiac output, limb blood perfusion and muscle metabolism are stable or increase during small muscle mass exercise or resting conditions, but are impaired during whole-body moderate to intense exercise. Progressive dehydration is also associated with an accelerated drop in perfusion and oxygen supply to the human brain during submaximal and maximal endurance exercise. Yet their consequences on aerobic metabolism are greater in the exercising muscles because of the much smaller functional oxygen extraction reserve. This review describes how dehydration differentially impacts physiological function during exercise requiring low compared to high functional demand, with an emphasis on the responses of the human brain, heart and skeletal muscles.
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19
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Parsons IT, Stacey MJ, Woods DR. Heat Adaptation in Military Personnel: Mitigating Risk, Maximizing Performance. Front Physiol 2019; 10:1485. [PMID: 31920694 PMCID: PMC6928107 DOI: 10.3389/fphys.2019.01485] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2019] [Accepted: 11/21/2019] [Indexed: 12/22/2022] Open
Abstract
The study of heat adaptation in military personnel offers generalizable insights into a variety of sporting, recreational and occupational populations. Conversely, certain characteristics of military employment have few parallels in civilian life, such as the imperative to achieve mission objectives during deployed operations, the opportunity to undergo training and selection for elite units or the requirement to fulfill essential duties under prolonged thermal stress. In such settings, achieving peak individual performance can be critical to organizational success. Short-notice deployment to a hot operational or training environment, exposure to high intensity exercise and undertaking ceremonial duties during extreme weather may challenge the ability to protect personnel from excessive thermal strain, especially where heat adaptation is incomplete. Graded and progressive acclimatization can reduce morbidity substantially and impact on mortality rates, yet individual variation in adaptation has the potential to undermine empirical approaches. Incapacity under heat stress can present the military with medical, occupational and logistic challenges requiring dynamic risk stratification during initial and subsequent heat stress. Using data from large studies of military personnel observing traditional and more contemporary acclimatization practices, this review article (1) characterizes the physical challenges that military training and deployed operations present (2) considers how heat adaptation has been used to augment military performance under thermal stress and (3) identifies potential solutions to optimize the risk-performance paradigm, including those with broader relevance to other populations exposed to heat stress.
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Affiliation(s)
- Iain T. Parsons
- Academic Department of Military Medicine, Research and Clinical Innovation, Royal Centre for Defence Medicine, Birmingham, United Kingdom
- School of Cardiovascular Medicine & Sciences, Faculty of Life Sciences & Medicine, King’s College London, London, United Kingdom
| | - Michael J. Stacey
- Academic Department of Military Medicine, Research and Clinical Innovation, Royal Centre for Defence Medicine, Birmingham, United Kingdom
- Department of Diabetes and Endocrinology, Imperial College Healthcare NHS Trust, London, United Kingdom
| | - David R. Woods
- Academic Department of Military Medicine, Research and Clinical Innovation, Royal Centre for Defence Medicine, Birmingham, United Kingdom
- Department of Sport and Exercise Endocrinology, Carnegie Research Institute, Leeds Beckett University, Leeds, United Kingdom
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20
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Engelland RE, Hemingway HW, Tomasco OG, Olivencia-Yurvati AH, Romero SA. Acute lower leg hot water immersion protects macrovascular dilator function following ischaemia-reperfusion injury in humans. Exp Physiol 2019; 105:302-311. [PMID: 31707732 DOI: 10.1113/ep088154] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Accepted: 11/08/2019] [Indexed: 12/14/2022]
Abstract
NEW FINDINGS • What is the central question of this study? What is the effect of lower leg hot water immersion on vascular ischaemia-reperfusion injury induced in the arm of young healthy humans? • What is the main finding and its importance? Lower leg hot water immersion successfully protects against vascular ischaemia-reperfusion injury in humans. This raises the possibility that targeted heating of the lower legs may be an alternative therapeutic approach to whole-body heating that is equally efficacious at protecting against vascular ischaemia-reperfusion injury. ABSTRACT Reperfusion that follows a period of ischaemia paradoxically reduces vasodilator function in humans and contributes to the tissue damage associated with an ischaemic event. Acute whole-body hot water immersion protects against vascular ischaemia-reperfusion (I-R) injury in young healthy humans. However, the effect of acute lower leg heating on I-R injury is unclear. Therefore, the purpose of this study was to test the hypothesis that, compared with thermoneutral control immersion, acute lower leg hot water immersion would prevent the decrease in macro- and microvascular dilator functions following I-R injury in young healthy humans. Ten young healthy subjects (5 female) immersed their lower legs into a circulated water bath for 60 min under two randomized conditions: (1) thermoneutral control immersion (∼33°C) and (2) hot water immersion (∼42°C). Macrovascular (brachial artery flow-mediated dilatation) and microvascular (forearm reactive hyperaemia) dilator functions were assessed using Doppler ultrasound at three time points: (1) pre-immersion, (2) 60 min post-immersion, and (3) post-I/R (20 min of arm ischaemia followed by 20 min of reperfusion). Ischaemia-reperfusion injury reduced macrovascular dilator function following control immersion (pre-immersion 6.0 ± 2.1% vs. post-I/R 3.6 ± 2.1%; P < 0.05), but was well-maintained with prior hot water immersion (pre-immersion 5.8 ± 2.1% vs. post-I/R 5.3 ± 2.1%; P = 0.8). Microvascular dilator function did not differ between conditions or across time. Taken together, acute lower leg hot water immersion prevents the decrease in macrovascular dilator function that occurs following I-R injury in young healthy humans.
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Affiliation(s)
- Rachel E Engelland
- Human Vascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - Holden W Hemingway
- Human Vascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - Olivia G Tomasco
- Human Vascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - Albert H Olivencia-Yurvati
- Human Vascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA.,Department of Surgery, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - Steven A Romero
- Human Vascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
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21
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Tai Y, Saeki K, Yamagami Y, Yoshimoto K, Kurumatani N, Nishio K, Obayashi K. Association between timing of hot water bathing before bedtime and night-/sleep-time blood pressure and dipping in the elderly: a longitudinal analysis for repeated measurements in home settings. Chronobiol Int 2019; 36:1714-1722. [DOI: 10.1080/07420528.2019.1675685] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Affiliation(s)
- Yoshiaki Tai
- Department of General Medicine, Nara Medical University School of Medicine, Nara, Japan
- Department of Epidemiology, Nara Medical University School of Medicine, Nara, Japan
| | - Keigo Saeki
- Department of Epidemiology, Nara Medical University School of Medicine, Nara, Japan
| | - Yuki Yamagami
- Department of Epidemiology, Nara Medical University School of Medicine, Nara, Japan
| | - Kiyomi Yoshimoto
- Department of General Medicine, Nara Medical University School of Medicine, Nara, Japan
| | - Norio Kurumatani
- Department of Epidemiology, Nara Medical University School of Medicine, Nara, Japan
| | - Kenji Nishio
- Department of General Medicine, Nara Medical University School of Medicine, Nara, Japan
| | - Kenji Obayashi
- Department of Epidemiology, Nara Medical University School of Medicine, Nara, Japan
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22
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Bihari S, Wiersema UF, Perry R, Schembri D, Bouchier T, Dixon D, Wong T, Bersten AD. Efficacy and safety of 20% albumin fluid loading in healthy subjects: a comparison of four resuscitation fluids. J Appl Physiol (1985) 2019; 126:1646-1660. [DOI: 10.1152/japplphysiol.01058.2018] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Recently, buffered salt solutions and 20% albumin (small volume resuscitation) have been advocated as an alternative fluid for intravenous resuscitation. The relative comparative efficacy and potential adverse effects of these solutions have not been evaluated. In a randomized, double blind, cross-over study of six healthy male subjects we compared the pulmonary and hemodynamic effects of intravenous administration of 30 ml/kg of 0.9% saline, Hartmann's solution and 4% albumin, and 6 ml/kg of 20% albumin (albumin dose equivalent). Lung tests (spirometry, ultrasound, impulse oscillometry, diffusion capacity, and plethysmography), two- to three-dimensional Doppler echocardiography, carotid applanation tonometry, blood gases, serum/urine markers of endothelial, and kidney injury were measured before and after each fluid bolus. Data were analyzed with repeated measures ANOVA with effect of fluid type examined as an interaction. Crystalloids caused lung edema [increase in ultrasound B line ( P = 0.006) and airway resistance ( P = 0.009)], but evidence of lung injury [increased angiopoietin-2 ( P = 0.019)] and glycocalyx injury [increased syndecan ( P = 0.026)] was only observed with 0.9% saline. The colloids caused greater left atrial stretch, decrease in lung volumes, and increase in diffusion capacity than the crystalloids, but without pulmonary edema. Stroke work increased proportionally to increase in preload with all four fluids ( R2 = 0.71). There was a greater increase in cardiac output and stroke volume after colloid administration, associated with a reduction in afterload. Hartmann’s solution did not significantly alter ventricular performance. Markers of kidney injury were not affected by any of the fluids administrated. Bolus administration of 20% albumin is both effective and safe in healthy subjects. NEW & NOTEWORTHY Bolus administration of 20% albumin is both effective and safe in healthy subjects when compared with other commonly available crystalloids and colloidal solution.
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Affiliation(s)
- Shailesh Bihari
- Intensive and Critical Care Unit, Flinders Medical Centre, Bedford Park, South Australia, Australia
- College of Medicine and Public Health, Flinders University, Adelaide, South Australia, Australia
| | - Ubbo F Wiersema
- Intensive and Critical Care Unit, Flinders Medical Centre, Bedford Park, South Australia, Australia
| | - Rebecca Perry
- College of Medicine and Public Health, Flinders University, Adelaide, South Australia, Australia
- Department of Cardiovascular Medicine, Flinders Medical Centre, Bedford Park, South Australia, Australia
- Department of Heart Health, South Australian Health and Medical Research Institute, Adelaide, Australia
| | - David Schembri
- Department of Respiratory Medicine, Flinders Medical Centre, Bedford Park, South Australia, Australia
| | - Tara Bouchier
- College of Medicine and Public Health, Flinders University, Adelaide, South Australia, Australia
| | - Dani Dixon
- Intensive and Critical Care Unit, Flinders Medical Centre, Bedford Park, South Australia, Australia
- College of Medicine and Public Health, Flinders University, Adelaide, South Australia, Australia
| | - Teresa Wong
- Intensive and Critical Care Unit, Flinders Medical Centre, Bedford Park, South Australia, Australia
| | - Andrew D Bersten
- Intensive and Critical Care Unit, Flinders Medical Centre, Bedford Park, South Australia, Australia
- College of Medicine and Public Health, Flinders University, Adelaide, South Australia, Australia
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23
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Goswami N, Blaber AP, Hinghofer-Szalkay H, Convertino VA. Lower Body Negative Pressure: Physiological Effects, Applications, and Implementation. Physiol Rev 2019; 99:807-851. [PMID: 30540225 DOI: 10.1152/physrev.00006.2018] [Citation(s) in RCA: 109] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
This review presents lower body negative pressure (LBNP) as a unique tool to investigate the physiology of integrated systemic compensatory responses to altered hemodynamic patterns during conditions of central hypovolemia in humans. An early review published in Physiological Reviews over 40 yr ago (Wolthuis et al. Physiol Rev 54: 566-595, 1974) focused on the use of LBNP as a tool to study effects of central hypovolemia, while more than a decade ago a review appeared that focused on LBNP as a model of hemorrhagic shock (Cooke et al. J Appl Physiol (1985) 96: 1249-1261, 2004). Since then there has been a great deal of new research that has applied LBNP to investigate complex physiological responses to a variety of challenges including orthostasis, hemorrhage, and other important stressors seen in humans such as microgravity encountered during spaceflight. The LBNP stimulus has provided novel insights into the physiology underlying areas such as intolerance to reduced central blood volume, sex differences concerning blood pressure regulation, autonomic dysfunctions, adaptations to exercise training, and effects of space flight. Furthermore, approaching cardiovascular assessment using prediction models for orthostatic capacity in healthy populations, derived from LBNP tolerance protocols, has provided important insights into the mechanisms of orthostatic hypotension and central hypovolemia, especially in some patient populations as well as in healthy subjects. This review also presents a concise discussion of mathematical modeling regarding compensatory responses induced by LBNP. Given the diverse applications of LBNP, it is to be expected that new and innovative applications of LBNP will be developed to explore the complex physiological mechanisms that underline health and disease.
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Affiliation(s)
- Nandu Goswami
- Physiology Section, Otto Loewi Research Center for Vascular Biology, Immunology and Inflammation, Medical University of Graz , Graz , Austria ; Department of Biomedical Physiology and Kinesiology, Simon Fraser University , Burnaby, British Columbia , Canada ; Battlefield Health & Trauma Center for Human Integrative Physiology, Combat Casualty Care Research Program, US Army Institute of Surgical Research, JBSA Fort Sam Houston, Texas
| | - Andrew Philip Blaber
- Physiology Section, Otto Loewi Research Center for Vascular Biology, Immunology and Inflammation, Medical University of Graz , Graz , Austria ; Department of Biomedical Physiology and Kinesiology, Simon Fraser University , Burnaby, British Columbia , Canada ; Battlefield Health & Trauma Center for Human Integrative Physiology, Combat Casualty Care Research Program, US Army Institute of Surgical Research, JBSA Fort Sam Houston, Texas
| | - Helmut Hinghofer-Szalkay
- Physiology Section, Otto Loewi Research Center for Vascular Biology, Immunology and Inflammation, Medical University of Graz , Graz , Austria ; Department of Biomedical Physiology and Kinesiology, Simon Fraser University , Burnaby, British Columbia , Canada ; Battlefield Health & Trauma Center for Human Integrative Physiology, Combat Casualty Care Research Program, US Army Institute of Surgical Research, JBSA Fort Sam Houston, Texas
| | - Victor A Convertino
- Physiology Section, Otto Loewi Research Center for Vascular Biology, Immunology and Inflammation, Medical University of Graz , Graz , Austria ; Department of Biomedical Physiology and Kinesiology, Simon Fraser University , Burnaby, British Columbia , Canada ; Battlefield Health & Trauma Center for Human Integrative Physiology, Combat Casualty Care Research Program, US Army Institute of Surgical Research, JBSA Fort Sam Houston, Texas
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24
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Tseng MF, Chou CL, Chung CH, Chien WC, Chen YK, Yang HC, Chu P. Association between heat stroke and ischemic heart disease: A national longitudinal cohort study in Taiwan. Eur J Intern Med 2019; 59:97-103. [PMID: 30297250 DOI: 10.1016/j.ejim.2018.09.019] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Revised: 09/21/2018] [Accepted: 09/27/2018] [Indexed: 12/16/2022]
Abstract
The purpose of this study is to determine the relationship between heat stroke and ischemic heart disease (IHD), in a nationwide population using a longitudinal approach. We retrospectively examined the data from the National Health Insurance Research Database (NHIRD) in Taiwan, for patients examined between 2000 and 2013. In total, 628 patients with a heat stroke episode were enrolled and matched with 1256 patients without any history of a heat stroke episode by propensity score matching at a ratio of 1:2. The mean follow-up years of the heat stroke group was 11.89 years and the mean follow up of the control group was 11.51 years. An association between heat stroke episodes and IHD (log-rank p < .001) was found in a univariate cox regression analysis. After multivariate adjustment, age, comorbidities (hypertension, diabetes, stroke), and lower insurance premiums were associated with IHD events in patients who had a heat stroke. IHD was independently associated with heat stroke following cox multivariate regression analysis and patients with a heat stroke episode had a higher incidence of IHD events compared to those without any heat stroke episode (2598.41/105 person-years vs. 1286.14/105 person-years, adjusted hazard ratio 3.527, 95% CI: 2.078-4.032, p < .001). The onset of IHD in patients who suffered a heat stroke was earlier than in those without a heat stroke episode (2.08 ± 3.45 vs. 3.61 ± 3.25 years, p < .001). In conclusion, clinicians should be aware about evaluating the IHD risk following a heat stroke episode in a patient.
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Affiliation(s)
- Min-Feng Tseng
- Department of Internal Medicine, Zuoying Branch of Kaohsiung Armed Forces General Hospital, Kaohsiung, Taiwan; Division of Nephrology, Department of Internal Medicine, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan
| | - Chu-Lin Chou
- Division of Nephrology, Department of Internal Medicine, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan; Department of Medical Research, Ping-Tung Christian Hospital, Ping-Tung, Taiwan
| | - Chi-Hsiang Chung
- School of Public Health, National Defense Medical Center, Taipei, Taiwan; Taiwanese Injury Prevention and Safety Promotion Association, Taipei, Taiwan
| | - Wu-Chien Chien
- School of Public Health, National Defense Medical Center, Taipei, Taiwan.
| | - Ying-Kai Chen
- Department of Internal Medicine, Zuoying Branch of Kaohsiung Armed Forces General Hospital, Kaohsiung, Taiwan
| | - Hsiu-Chien Yang
- Department of Internal Medicine, Zuoying Branch of Kaohsiung Armed Forces General Hospital, Kaohsiung, Taiwan
| | - Pauling Chu
- Division of Nephrology, Department of Internal Medicine, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan; Center for the Prevention and Treatment of Heat Stroke, Tri-Service General Hospital, Taipei, Taiwan.
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25
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Crandall CG, Rickards CA, Johnson BD. Impact of environmental stressors on tolerance to hemorrhage in humans. Am J Physiol Regul Integr Comp Physiol 2018; 316:R88-R100. [PMID: 30517019 DOI: 10.1152/ajpregu.00235.2018] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Hemorrhage is a leading cause of death in military and civilian settings, and ~85% of potentially survivable battlefield deaths are hemorrhage-related. Soldiers and civilians are exposed to a number of environmental and physiological conditions that have the potential to alter tolerance to a hemorrhagic insult. The objective of this review is to summarize the known impact of commonly encountered environmental and physiological conditions on tolerance to hemorrhagic insult, primarily in humans. The majority of the studies used lower body negative pressure (LBNP) to simulate a hemorrhagic insult, although some studies employed incremental blood withdrawal. This review addresses, first, the use of LBNP as a model of hemorrhage-induced central hypovolemia and, then, the effects of the following conditions on tolerance to LBNP: passive and exercise-induced heat stress with and without hypohydration/dehydration, exposure to hypothermia, and exposure to altitude/hypoxia. An understanding of the effects of these environmental and physiological conditions on responses to a hemorrhagic challenge, including tolerance, can enable development and implementation of targeted strategies and interventions to reduce the impact of such conditions on tolerance to a hemorrhagic insult and, ultimately, improve survival from blood loss injuries.
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Affiliation(s)
- Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center , Dallas, Texas
| | - Caroline A Rickards
- Department of Physiology and Anatomy, University of North Texas Health Science Center , Fort Worth, Texas
| | - Blair D Johnson
- Department of Exercise and Nutrition Sciences, University at Buffalo , Buffalo, New York
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26
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Rozenbaum Z, Topilsky Y, Khoury S, Assi M, Balchyunayte A, Laufer-Perl M, Berliner S, Pereg D, Entin-Meer M, Havakuk O. Relationship between climate and hemodynamics according to echocardiography. J Appl Physiol (1985) 2018; 126:322-329. [PMID: 30462569 DOI: 10.1152/japplphysiol.00519.2018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Studies performed in controlled laboratory conditions have shown that environmental thermal application may induce various circulatory changes. We aimed to demonstrate the effect of local climate on hemodynamics according to echocardiography. Echocardiographic studies conducted in ambulatory patients, 18 yr of age or older, between January 2012 and July 2016, at our medical center, for whom climate data on the day of the echocardiogram study were available, were retrospectively included in case climate data. Discomfort index, apparent temperature, temperature-humidity index, and thermal index were computed. Echocardiograms conducted in hotter months (June-November) were compared with those done in colder months (December-May). The cohort consisted of 11,348 individuals, 46.2% women, and mean age of 57.9 ± 18.1 yr. Climate indexes correlated directly with stroke volume ( r = 0.039) and e' (lateral r = 0.047; septal r = 0.038), and inversely with systolic pulmonary artery pressure (SPAP; r = -0.038) (all P values < 0.05). After adjustment for age and sex, echocardiograms conducted during June-November had a lower chance to show e' septal < 7 cm/s (odds ratio 0.88, 95% confidence interval 0.78-0.98, P = 0.017) and SPAP > 40 mmHg (odds ratio 0.81, 95% confidence interval 0.67-0.99, P = 0.04) compared with those conducted in other months. The authors concluded that climate may affect hemodynamics, according to echocardiographic assessment in ambulatory patients. NEW & NOTEWORTHY In the present study, we examined 11,348 individuals who underwent ambulatory echocardiography. Analyses of the echocardiographic studies demonstrated that environmental thermal stress, i.e., climate, may affect hemodynamics. Most notably were the effects on diastolic function. Higher values of mitral e', stroke volume, as well as ejection fraction, and lower values of systolic pulmonary artery pressure and tricuspid regurgitation were demonstrated on hotter days and seasons.
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Affiliation(s)
- Zach Rozenbaum
- Department of Cardiology, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - Yan Topilsky
- Department of Cardiology, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - Shafik Khoury
- Department of Cardiology, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - Milwidsky Assi
- Department of Cardiology, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - Asta Balchyunayte
- Department of Internal Medicine, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - Michal Laufer-Perl
- Department of Cardiology, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - Shlomo Berliner
- Department of Internal Medicine, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - David Pereg
- Department of Cardiology, Meir Medical Center, Kfar Saba, Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - Michal Entin-Meer
- Cardiovascular Research Laboratory, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
| | - Ofer Havakuk
- Department of Cardiology, Tel Aviv Medical Center , Tel Aviv , Israel.,Sackler Faculty of Medicine, Tel Aviv University , Tel Aviv , Israel
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27
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Fu Q, Levine BD. Exercise and non-pharmacological treatment of POTS. Auton Neurosci 2018; 215:20-27. [PMID: 30001836 DOI: 10.1016/j.autneu.2018.07.001] [Citation(s) in RCA: 73] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2018] [Revised: 06/29/2018] [Accepted: 07/01/2018] [Indexed: 12/11/2022]
Abstract
Recent research has demonstrated that cardiovascular deconditioning (i.e., cardiac atrophy and hypovolemia) contributes significantly to the Postural Orthostatic Tachycardia Syndrome (POTS) and its functional disability. Therefore, physical reconditioning with exercise training and volume expansion via increased salt and fluid intake should be initiated early in the course of treatment for patients with POTS if possible. The use of horizontal exercise (e.g., rowing, swimming, recumbent bike, etc.) at the beginning is a critical strategy, allowing patients to exercise while avoiding the upright posture that elicits their POTS symptoms. As patients become increasingly fit, the duration and intensity of exercise should be progressively increased, and upright exercise can be gradually added as tolerated. Supervised training is preferable to maximize functional capacity. Other non-pharmacological interventions, which include: 1) chronic volume expansion via sleeping in the head-up position; 2) reduction in venous pooling during orthostasis by lower body compression garments extending at least to the xiphoid or with an abdominal binder; and 3) physical countermeasure maneuvers, such as squeezing a rubber ball, leg crossing, muscle pumping, squatting, negative-pressure breathing, etc., may also be effective in preventing orthostatic intolerance and managing acute clinical symptoms in POTS patients. However, randomized clinical trials are needed to evaluate the efficacies of these non-pharmacological treatments of POTS.
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Affiliation(s)
- Qi Fu
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, The University of Texas Southwestern Medical Center, Dallas, TX, USA.
| | - Benjamin D Levine
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, The University of Texas Southwestern Medical Center, Dallas, TX, USA
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29
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Schlader ZJ, Coleman GL, Sackett JR, Sarker S, Chapman CL, Hostler D, Johnson BD. Behavioral thermoregulation in older adults with cardiovascular co-morbidities. Temperature (Austin) 2017; 5:70-85. [PMID: 29687045 PMCID: PMC5902208 DOI: 10.1080/23328940.2017.1379585] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2017] [Revised: 09/01/2017] [Accepted: 09/06/2017] [Indexed: 12/21/2022] Open
Abstract
We tested the hypotheses that older adults with cardiovascular co-morbidities will demonstrate greater changes in body temperature and exaggerated changes in blood pressure before initiating thermal behavior. We studied twelve healthy younger adults (Younger, 25 ± 4 y) and six older adults ('At Risk', 67 ± 4 y) taking prescription medications for at least two of the following conditions: hypertension, type II diabetes, hypercholesterolemia. Subjects underwent a 90-min test in which they voluntarily moved between cool (18.1 ± 1.8°C, RH: 29 ± 5%) and warm (40.2 ± 0.3°C, RH: 20 ± 0%) rooms when they felt 'too cool' (C→W) or 'too warm' (W→C). Mean skin and intestinal temperatures and blood pressure were measured. Data were analyzed as a change from pretest baseline. Changes in mean skin temperature were not different between groups at C→W (Younger: +0.2 ± 0.8°C, 'At Risk': +0.7 ± 1.8°C, P = 0.51) or W→C (Younger: +2.7 ± 0.6°C, 'At Risk': +2.9 ± 1.9°C, P = 0.53). Changes in intestinal temperature were not different at C→W (Younger: 0.0 ± 0.1°C, 'At Risk': +0.1 ± 0.2, P = 0.11), but differed at W→C (-0.1 ± 0.2°C vs. +0.1 ± 0.3°C, P = 0.02). Systolic pressure at C→W increased (Younger: +10 ± 9 mmHg, 'At Risk': +24 ± 17 mmHg) and at W→C decreased (Younger: -4 ± 13 mmHg, 'At Risk': -23 ± 19 mmHg) to a greater extent in 'At Risk' (P ≤ 0.05). Differences were also apparent for diastolic pressure at C→W (Younger: -2 ± 4 mmHg, 'At Risk': +17 ± 23 mmHg, P < 0.01), but not at W→C (Younger Y: +4 ± 13 mmHg, 'At Risk': -1 ± 6 mmHg, P = 0.29). Despite little evidence for differential control of thermal behavior, the initiation of behavior in 'at risk' older adults is preceded by exaggerated blood pressure responses.
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Affiliation(s)
- Zachary J. Schlader
- Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, USA
| | - Gregory L. Coleman
- Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, USA
| | - James R. Sackett
- Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, USA
| | - Suman Sarker
- Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, USA
| | - Christopher L. Chapman
- Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, USA
| | - David Hostler
- Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, USA
| | - Blair D. Johnson
- Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, USA
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30
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Gagnon D, Romero SA, Ngo H, Sarma S, Cornwell WK, Poh PYS, Stoller D, Levine BD, Crandall CG. Volume loading augments cutaneous vasodilatation and cardiac output of heat stressed older adults. J Physiol 2017; 595:6489-6498. [PMID: 28833129 DOI: 10.1113/jp274742] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Accepted: 08/11/2017] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Age-related changes in cutaneous microvascular and cardiac functions limit the extent of cutaneous vasodilatation and the increase in cardiac output that healthy older adults can achieve during passive heat stress. However, it is unclear if these age-related changes in microvascular and cardiac functions maximally restrain the levels of cutaneous vasodilatation and cardiac output that healthy older adults can achieve during heat stress. We observed that rapid volume loading, performed during passive heat stress, augments both cutaneous vasodilatation and cardiac output in healthy older humans. These findings demonstrate that the microcirculation of healthy aged skin can further dilate during passive heat exposure, despite peripheral limitations to vasodilatation. Furthermore, healthy older humans can augment cardiac output when cardiac pre-load is increased during heat stress. ABSTRACT Primary ageing markedly attenuates cutaneous vasodilatation and the increase in cardiac output during passive heating. However, it remains unclear if these responses are maximally restrained by age-related changes in cutaneous microvascular and cardiac functions. We hypothesized that rapid volume loading performed during heat stress would increase cardiac output in older adults without parallel increases in cutaneous vasodilatation. Twelve young (Y: 26 ± 5 years) and ten older (O: 69 ± 3 years) healthy adults were passively heated until core temperature increased by 1.5°C. Cardiac output (thermodilution), forearm vascular conductance (FVC, venous occlusion plethysmography) and cutaneous vascular conductance (CVC, laser-Doppler) were measured before and after rapid infusion of warmed saline (15 mL kg-1 , ∼7 min). While heat stressed, but prior to saline infusion, cardiac output (O: 6.8 ± 0.4 vs. Y: 9.4 ± 0.6 L min-1 ), FVC (O: 0.08 ± 0.01 vs. Y: 0.17 ± 0.02 mL (100 mL min-1 mmHg-1 )-1 ), and CVC (O: 1.29 ± 0.34 vs. Y: 1.93 ± 0.30 units mmHg-1 ) were lower in older adults (all P < 0.01). Rapid saline infusion increased cardiac output (O: +1.9 ± 0.3, Y: +1.8 ± 0.7 L min-1 ), FVC (O: +0.015 ± 0.007, Y: +0.048 ± 0.013 mL (100 mL min-1 mmHg-1 )-1 ), and CVC (O: +0.28 ± 0.10, Y: +0.29 ± 0.16 units mmHg-1 ) in both groups (all P < 0.01). The absolute increase in cardiac output and CVC were similar between groups, whereas FVC increased to a greater extent in young adults (P < 0.01). These results demonstrate that healthy older adults can achieve greater levels of cutaneous vasodilatation and cardiac output during passive heating.
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Affiliation(s)
- Daniel Gagnon
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX, USA.,Cardiovascular Prevention and Rehabilitation Centre, Montreal Heart Institute Research Centre, Montréal, QC, Canada.,Département de pharmacologie et physiologie, Faculté de Médecine, Université de Montréal, Montréal, QC, Canada
| | - Steven A Romero
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Hai Ngo
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Satyam Sarma
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - William K Cornwell
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX, USA.,Department of Medicine-Cardiology, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
| | - Paula Y S Poh
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Douglas Stoller
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Benjamin D Levine
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX, USA
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31
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James CA, Richardson AJ, Watt PW, Willmott AG, Gibson OR, Maxwell NS. Short-term heat acclimation improves the determinants of endurance performance and 5-km running performance in the heat. Appl Physiol Nutr Metab 2017; 42:285-294. [DOI: 10.1139/apnm-2016-0349] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study investigated the effect of 5 days of controlled short-term heat acclimation (STHA) on the determinants of endurance performance and 5-km performance in runners, relative to the impairment afforded by moderate heat stress. A control group (CON), matched for total work and power output (2.7 W·kg−1), differentiated thermal and exercise contributions of STHA on exercise performance. Seventeen participants (10 STHA, 7 CON) completed graded exercise tests (GXTs) in cool (13 °C, 50% relative humidity (RH), pre-training) and hot conditions (32 °C, 60% RH, pre- and post-training), as well as 5-km time trials (TTs) in the heat, pre- and post-training. STHA reduced resting (p = 0.01) and exercising (p = 0.04) core temperature alongside a smaller change in thermal sensation (p = 0.04). Both groups improved the lactate threshold (LT, p = 0.021), lactate turnpoint (LTP, p = 0.005) and velocity at maximal oxygen consumption (vV̇O2max; p = 0.031) similarly. Statistical differences between training methods were observed in TT performance (STHA, −6.2(5.5)%; CON, −0.6(1.7)%, p = 0.029) and total running time during the GXT (STHA, +20.8(12.7)%; CON, +9.8(1.2)%, p = 0.006). There were large mean differences in change in maximal oxygen consumption between STHA +4.0(2.2) mL·kg−1·min−1 (7.3(4.0)%) and CON +1.9(3.7) mL·kg−1·min−1 (3.8(7.2)%). Running economy (RE) deteriorated following both training programmes (p = 0.008). Similarly, RE was impaired in the cool GXT, relative to the hot GXT (p = 0.004). STHA improved endurance running performance in comparison with work-matched normothermic training, despite equality of adaptation for typical determinants of performance (LT, LTP, vV̇O2max). Accordingly, these data highlight the ergogenic effect of STHA, potentially via greater improvements in maximal oxygen consumption and specific thermoregulatory and associated thermal perception adaptations absent in normothermic training.
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Affiliation(s)
- Carl A. James
- Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Eastbourne BN20 7UR, UK
- National Sports Institute of Malaysia, Institut Sukan Negara, Bukit Jalil Stadium, Kuala Lumpur 57000, Malaysia
| | - Alan J. Richardson
- Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Eastbourne BN20 7UR, UK
| | - Peter W. Watt
- Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Eastbourne BN20 7UR, UK
| | - Ashley G.B. Willmott
- Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Eastbourne BN20 7UR, UK
| | - Oliver R. Gibson
- Centre for Human Performance, Exercise and Rehabilitation (CHPER), Brunel University London UB8 3PH, UK
| | - Neil S. Maxwell
- Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Eastbourne BN20 7UR, UK
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32
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Wilson TE. Renal sympathetic nerve, blood flow, and epithelial transport responses to thermal stress. Auton Neurosci 2016; 204:25-34. [PMID: 28043810 DOI: 10.1016/j.autneu.2016.12.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2016] [Revised: 11/28/2016] [Accepted: 12/20/2016] [Indexed: 12/12/2022]
Abstract
Thermal stress is a profound sympathetic stress in humans; kidney responses involve altered renal sympathetic nerve activity (RSNA), renal blood flow, and renal epithelial transport. During mild cold stress, RSNA spectral power but not total activity is altered, renal blood flow is maintained or decreased, and epithelial transport is altered consistent with a sympathetic stress coupled with central volume loaded state. Hypothermia decreases RSNA, renal blood flow, and epithelial transport. During mild heat stress, RSNA is increased, renal blood flow is decreased, and epithelial transport is increased consistent with a sympathetic stress coupled with a central volume unloaded state. Hyperthermia extends these directional changes, until heat illness results. Because kidney responses are very difficult to study in humans in vivo, this review describes and qualitatively evaluates an in vivo human skin model of sympathetically regulated epithelial tissue compared to that of the nephron. This model utilizes skin responses to thermal stress, involving 1) increased skin sympathetic nerve activity (SSNA), decreased skin blood flow, and suppressed eccrine epithelial transport during cold stress; and 2) increased SSNA, skin blood flow, and eccrine epithelial transport during heat stress. This model appears to mimic aspects of the renal responses. Investigations of skin responses, which parallel certain renal responses, may aid understanding of epithelial-sympathetic nervous system interactions during cold and heat stress.
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Affiliation(s)
- Thad E Wilson
- Division of Biomedical Sciences, Marian University College of Osteopathic Medicine, Indianapolis, IN, USA.
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Krnjajic D, Allen DR, Butts CL, Keller DM. Carotid baroreflex control of heart rate is enhanced, while control of mean arterial pressure is preserved during whole body heat stress in young healthy men. Am J Physiol Regul Integr Comp Physiol 2016; 311:R735-R741. [DOI: 10.1152/ajpregu.00152.2016] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2016] [Accepted: 07/29/2016] [Indexed: 11/22/2022]
Abstract
Whole body heat stress (WBH) results in numerous cardiovascular alterations that ultimately reduce orthostatic tolerance. While impaired carotid baroreflex (CBR) function during WBH has been reported as a potential reason for this decrement, study design considerations may limit interpretation of previous findings. We sought to test the hypothesis that CBR function is unaltered during WBH. CBR function was assessed in 10 healthy male subjects (age: 26 ± 3; height: 185 ± 7 cm; weight: 82 ± 10 kg; BMI: 24 ± 3 kg/m2; means ± SD) using 5-s trials of neck pressure (+45, +30, and +15 Torr) and neck suction (−20, −40, −60, and −80 Torr) during normothermia (NT) and passive WBH (Δ core temp ∼1°C). Analyses of stimulus response curves (four-parameter logistic model) for CBR control of heart rate (CBR-HR) and mean arterial pressure (CBR-MAP), as well as separate two-way ANOVA of the hypotensive and hypertensive stimuli (factor 1: thermal condition, factor 2: chamber pressure), were performed. For CBR-HR, maximal gain was increased during WBH (−0.73 ± 0.11) compared with NT (−0.39 ± 0.04, mean ± SE, P = 0.03). In addition, the CBR-HR responding range was increased during WBH (33 ± 5) compared with NT (19 ± 2 bpm, P = 0.03). Separate analysis of hypertensive stimulation revealed enhanced HR responses during WBH at −40, −60, and −80 Torr (condition × chamber pressure interaction, P = 0.049) compared with NT. For CBR-MAP, both logistic analysis and separate two-way ANOVA revealed no differences during WBH. Therefore, in response to passive WBH, CBR control of heart rate (enhanced) and arterial pressure (no change) is well preserved.
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Affiliation(s)
- Davor Krnjajic
- Department of Kinesiology, University of Texas, Arlington, Arlington, Texas
| | - Dustin R. Allen
- Department of Kinesiology, University of Texas, Arlington, Arlington, Texas
| | - Cory L. Butts
- Department of Kinesiology, University of Texas, Arlington, Arlington, Texas
| | - David M. Keller
- Department of Kinesiology, University of Texas, Arlington, Arlington, Texas
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Gagnon D, Romero SA, Ngo H, Sarma S, Cornwell WK, Poh PYS, Stoller D, Levine BD, Crandall CG. Healthy aging does not compromise the augmentation of cardiac function during heat stress. J Appl Physiol (1985) 2016; 121:885-892. [PMID: 27609201 DOI: 10.1152/japplphysiol.00643.2016] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2016] [Accepted: 09/06/2016] [Indexed: 11/22/2022] Open
Abstract
During heat stress, stroke volume is maintained in young adults despite reductions in cardiac filling pressures. This is achieved by a general augmentation of cardiac function, highlighted by a left and upward shift of the Frank-Starling relation. In contrast, healthy aged adults are unable to maintain stroke volume during heat stress. We hypothesized that this would be associated with a lack of shift in the Frank-Starling relation. Frank-Starling relations were examined in 11 aged [69 ± 4 (SD) yr, 4 men/7 women] and 12 young (26 ± 5 yr, 6 men/6 women) adults during normothermic and heat stress (1.5°C increase in core temperature) conditions. During heat stress, increases in cardiac output were attenuated in aged adults (+2.5 ± 0.3 (95% CI) vs. young: +4.5 ± 0.5 l/min, P < 0.01) because of an attenuated chronotropic response (+30 ± 4 vs. young: +42 ± 5 beats/min, P < 0.01). In contrast to our hypothesis, a leftward shift of the Frank-Starling relation maintained stroke volume during heat stress in aged adults (76 ± 8 vs. normothermic: 74 ± 8 ml, P = 0.38) despite reductions in cardiac filling pressure (6.6 ± 1.0 vs. normothermic: 8.9 ± 1.1 mmHg, P < 0.01). In a subset of participants, volume loading was used to return cardiac filling pressure during heat stress to normothermic values, which resulted in a greater stroke volume for a given cardiac filling pressure in both groups. These results demonstrate that the Frank-Starling relation shifts during heat stress in healthy young and aged adults, thereby preserving stroke volume despite reductions in cardiac filling pressures.
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Affiliation(s)
- Daniel Gagnon
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas; Cardiovascular Prevention and Rehabilitation Centre (ÉPIC), Montreal Heart Institute Research Centre, Montreal, Quebec, Canada; and Département de physiologie moléculaire et intégrative, Faculté de Médecine, Université de Montréal, Montreal, Quebec, Canada
| | - Steven A Romero
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - Hai Ngo
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - Satyam Sarma
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - William K Cornwell
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - Paula Y S Poh
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - Douglas Stoller
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - Benjamin D Levine
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas
| | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas;
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Dahl M, Hayes C, Steen Rasmussen B, Larsson A, Secher NH. Can a central blood volume deficit be detected by systolic pressure variation during spontaneous breathing? BMC Anesthesiol 2016; 16:58. [PMID: 27515038 PMCID: PMC4982018 DOI: 10.1186/s12871-016-0224-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2015] [Accepted: 07/14/2016] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND Whether during spontaneous breathing arterial pressure variations (APV) can detect a volume deficit is not established. We hypothesized that amplification of intra-thoracic pressure oscillations by breathing through resistors would enhance APV to allow identification of a reduced cardiac output (CO). This study tested that hypothesis in healthy volunteers exposed to central hypovolemia by head-up tilt. METHODS Thirteen healthy volunteers were exposed to central hypovolemia by 45° head-up tilt while breathing through a facemask with 7.5 cmH2O inspiratory and/or expiratory resistors. A brachial arterial catheter was used to measure blood pressure and thus systolic pressure variation (SPV), pulse pressure variation and stroke volume variation . Pulse contour analysis determined stroke volume (SV) and CO and we evaluated whether APV could detect a 10 % decrease in CO. RESULTS During head-up tilt SV decreased form 91 (±46) to 55 (±24) mL (mean ± SD) and CO from 5.8 (±2.9) to 4.0 (±1.8) L/min (p < 0.05), while heart rate increased (65 (±11) to 75 (±13) bpm; P < 0.05). Systolic pressure decreased from 127 (±14) to 121 (±13) mmHg during head-up tilt, while SPV tended to increase (from 21 (±15)% to 30 (±13)%). Yet during head-up tilt, a SPV ≥ 37 % predicted a decrease in CO ≥ 10 % with a sensitivity and specificity of 78 % and 100 %, respectively. CONCLUSION In spontaneously breathing healthy volunteers combined inspiratory and expiratory resistors enhance SPV during head-up tilted induced central hypovolemia and allow identifying a 10 % reduction in CO. Applying inspiratory and expiratory resistors might detect a fluid deficit in spontaneously breathing patients. TRIAL REGISTRATION ClinicalTrials.gov number NCT02549482 Registered September 10(th) 2015.
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Affiliation(s)
- Michael Dahl
- Department of Anesthesiology and Intensive Care Medicine, Aalborg University Hospital, Hobrovej 18-21, DK-9000, Aalborg, Denmark.
| | - Chris Hayes
- Department of Anesthesiology and Intensive Care Medicine, Aalborg University Hospital, Hobrovej 18-21, DK-9000, Aalborg, Denmark
| | - Bodil Steen Rasmussen
- Department of Anesthesiology and Intensive Care Medicine, Aalborg University Hospital, Hobrovej 18-21, DK-9000, Aalborg, Denmark
| | - Anders Larsson
- Hedenstierna laboratory, Section of Anesthesiology and Intensive Care, Department of Surgical Sciences, Uppsala University, ANIVA Ing. 70, 1. tv., S-75643, Uppsala, Sweden
| | - Niels H Secher
- Department of Anesthesiology, The Copenhagen Muscle Research Center Rigshospitalet 2043, University of Copenhagen, Blegdamsvej 9, DK-2100, Copenhagen, Denmark
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Bain AR, Nybo L, Ainslie PN. Cerebral Vascular Control and Metabolism in Heat Stress. Compr Physiol 2016; 5:1345-80. [PMID: 26140721 DOI: 10.1002/cphy.c140066] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
This review provides an in-depth update on the impact of heat stress on cerebrovascular functioning. The regulation of cerebral temperature, blood flow, and metabolism are discussed. We further provide an overview of vascular permeability, the neurocognitive changes, and the key clinical implications and pathologies known to confound cerebral functioning during hyperthermia. A reduction in cerebral blood flow (CBF), derived primarily from a respiratory-induced alkalosis, underscores the cerebrovascular changes to hyperthermia. Arterial pressures may also become compromised because of reduced peripheral resistance secondary to skin vasodilatation. Therefore, when hyperthermia is combined with conditions that increase cardiovascular strain, for example, orthostasis or dehydration, the inability to preserve cerebral perfusion pressure further reduces CBF. A reduced cerebral perfusion pressure is in turn the primary mechanism for impaired tolerance to orthostatic challenges. Any reduction in CBF attenuates the brain's convective heat loss, while the hyperthermic-induced increase in metabolic rate increases the cerebral heat gain. This paradoxical uncoupling of CBF to metabolism increases brain temperature, and potentiates a condition whereby cerebral oxygenation may be compromised. With levels of experimentally viable passive hyperthermia (up to 39.5-40.0 °C core temperature), the associated reduction in CBF (∼ 30%) and increase in cerebral metabolic demand (∼ 10%) is likely compensated by increases in cerebral oxygen extraction. However, severe increases in whole-body and brain temperature may increase blood-brain barrier permeability, potentially leading to cerebral vasogenic edema. The cerebrovascular challenges associated with hyperthermia are of paramount importance for populations with compromised thermoregulatory control--for example, spinal cord injury, elderly, and those with preexisting cardiovascular diseases.
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Affiliation(s)
- Anthony R Bain
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, Canada
| | - Lars Nybo
- Department of Nutrition, Exercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Philip N Ainslie
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, Canada
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Schlader ZJ, Sarker S, Mündel T, Coleman GL, Chapman CL, Sackett JR, Johnson BD. Hemodynamic responses upon the initiation of thermoregulatory behavior in young healthy adults. Temperature (Austin) 2016; 3:271-285. [PMID: 27857957 PMCID: PMC4965002 DOI: 10.1080/23328940.2016.1148938] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Revised: 01/26/2016] [Accepted: 01/27/2016] [Indexed: 11/30/2022] Open
Abstract
We tested the hypotheses that thermoregulatory behavior is initiated before changes in blood pressure and that skin blood flow upon the initiation of behavior is reflex mediated. Ten healthy young subjects moved between 40°C and 17°C rooms when they felt 'too warm' (W→C) or 'too cool' (C→W). Blood pressure, cardiac output, skin and rectal temperatures were measured. Changes in skin blood flow between locations were not different at 2 forearm locations. One was clamped at 34°C ensuring responses were reflex controlled. The temperature of the other was not clamped ensuring responses were potentially local and/or reflex controlled. Relative to pre-test Baseline, skin temperature was not different at C→W (33.5 ± 0.7°C, P = 0.24), but was higher at W→C (36.1 ± 0.5°C, P < 0.01). Rectal temperature was different from Baseline at C→W (-0.2 ± 0.1°C, P < 0.01) and W→C (-0.2 ± 0.1°C, P < 0.01). Blood pressure was different from Baseline at C→W (+7 ± 4 mmHg, P < 0.01) and W→C (-5 ± 5 mmHg, P < 0.01). Cardiac output was not different from Baseline at C→W (-0.1 ± 0.4 L/min, P = 0.56), but higher at W→C (0.4 ± 0.4 L/min, P < 0.01). Skin blood flow between locations was not different from Baseline at C→W (clamped: -6 ± 15 PU, not clamped: -3 ± 6 PU, P = 0.46) or W→C (clamped: +21 ± 23 PU, not clamped: +29 ± 15 PU, P = 0.26). These data indicate that the initiation of thermoregulatory behavior is preceded by moderate changes in blood pressure and that skin blood flow upon the initiation of this behavior is under reflex control.
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Affiliation(s)
- Zachary J. Schlader
- Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, USA
| | - Suman Sarker
- Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, USA
| | - Toby Mündel
- School of Sport and Exercise, Massey University, Palmerston North, New Zealand`
| | - Gregory L. Coleman
- Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, USA
| | | | - James R. Sackett
- Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, USA
| | - Blair D. Johnson
- Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, USA
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Schlader ZJ, Wilson TE, Crandall CG. Mechanisms of orthostatic intolerance during heat stress. Auton Neurosci 2015; 196:37-46. [PMID: 26723547 DOI: 10.1016/j.autneu.2015.12.005] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Revised: 11/30/2015] [Accepted: 12/14/2015] [Indexed: 01/04/2023]
Abstract
Heat stress profoundly and unanimously reduces orthostatic tolerance. This review aims to provide an overview of the numerous and multifactorial mechanisms by which this occurs in humans. Potential causal factors include changes in arterial and venous vascular resistance and blood distribution, and the modulation of cardiac output, all of which contribute to the inability to maintain cerebral perfusion during heat and orthostatic stress. A number of countermeasures have been established to improve orthostatic tolerance during heat stress, which alleviate heat stress induced central hypovolemia (e.g., volume expansion) and/or increase peripheral vascular resistance (e.g., skin cooling). Unfortunately, these countermeasures can often be cumbersome to use with populations prone to syncopal episodes. Identifying the mechanisms of inter-individual differences in orthostatic intolerance during heat stress has proven elusive, but could provide greater insights into the development of novel and personalized countermeasures for maintaining or improving orthostatic tolerance during heat stress. This development will be especially impactful in occuational settings and clinical situations that present with orthostatic intolerance and/or central hypovolemia. Such investigations should be considered of vital importance given the impending increased incidence of heat events, and associated cardiovascular challenges that are predicted to occur with the ensuing changes in climate.
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Affiliation(s)
- Zachary J Schlader
- Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, United States.
| | - Thad E Wilson
- Marian University College of Osteopathic Medicine, Indianapolis, IN, United States
| | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX, United States
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Greaney JL, Stanhewicz AE, Proctor DN, Alexander LM, Kenney WL. Impairments in central cardiovascular function contribute to attenuated reflex vasodilation in aged skin. J Appl Physiol (1985) 2015; 119:1411-20. [PMID: 26494450 PMCID: PMC4683344 DOI: 10.1152/japplphysiol.00729.2015] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Accepted: 10/20/2015] [Indexed: 01/08/2023] Open
Abstract
During supine passive heating, increases in skin blood flow (SkBF) and cardiac output (Qc) are both blunted in older adults. The aim here was to determine the effect of acutely correcting the peripheral vasodilatory capacity of aged skin on the integrated cardiovascular responses to passive heating. A secondary aim was to examine the SkBF-Qc relation during hyperthermia in the presence (upright posture) and absence (dynamic exercise) of challenges to central venous pressure. We hypothesized that greater increases in SkBF would be accompanied by greater increases in Qc. Eleven healthy older adults (69 ± 3 yr) underwent supine passive heating (0.8°C rise in core temperature; water-perfused suit) after ingesting sapropterin (BH4, a nitric oxide synthase cofactor; 10 mg/kg) or placebo (randomized double-blind crossover design). Twelve young (24 ± 1 yr) subjects served as a comparison group. SkBF (laser-Doppler flowmetry) and Qc (open-circuit acetylene wash-in) were measured during supine heating, heating + upright posture, and heating + dynamic exercise. Throughout supine and upright heating, sapropterin fully restored the SkBF response of older adults to that of young adults but Qc remained blunted. During heat + upright posture, SkBF failed to decrease in untreated older subjects. There were no age- or treatment-related differences in SkBF-Qc during dynamic exercise. The principal finding of this study was that the blunted Qc response to passive heat stress is directly related to age as opposed to the blunted peripheral vasodilatory capacity of aged skin. Furthermore, peripheral impairments to SkBF in the aged may contribute to inapposite responses during challenges to central venous pressure during hyperthermia.
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Affiliation(s)
- Jody L Greaney
- Department of Kinesiology, Noll Laboratory, The Pennsylvania State University, University Park, Pennsylvania
| | - Anna E Stanhewicz
- Department of Kinesiology, Noll Laboratory, The Pennsylvania State University, University Park, Pennsylvania
| | - David N Proctor
- Department of Kinesiology, Noll Laboratory, The Pennsylvania State University, University Park, Pennsylvania
| | - Lacy M Alexander
- Department of Kinesiology, Noll Laboratory, The Pennsylvania State University, University Park, Pennsylvania
| | - W Larry Kenney
- Department of Kinesiology, Noll Laboratory, The Pennsylvania State University, University Park, Pennsylvania
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Castellani JW, Tipton MJ. Cold Stress Effects on Exposure Tolerance and Exercise Performance. Compr Physiol 2015; 6:443-69. [PMID: 26756639 DOI: 10.1002/cphy.c140081] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Cold weather can have deleterious effects on health, tolerance, and performance. This paper will review the physiological responses and external factors that impact cold tolerance and physical performance. Tolerance is defined as the ability to withstand cold stress with minimal changes in physiological strain. Physiological and pathophysiological responses to short-term (cold shock) and long-term cold water and air exposure are presented. Factors (habituation, anthropometry, sex, race, and fitness) that influence cold tolerance are also reviewed. The impact of cold exposure on physical performance, especially aerobic performance, has not been thoroughly studied. The few studies that have been done suggest that aerobic performance is degraded in cold environments. Potential physiological mechanisms (decreases in deep body and muscle temperature, cardiovascular, and metabolism) are discussed. Likewise, strength and power are also degraded during cold exposure, primarily through a decline in muscle temperature. The review also discusses the concept of thermoregulatory fatigue, a reduction in the thermal effector responses of shivering and vasoconstriction, as a result of multistressor factors, including exhaustive exercise.
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Affiliation(s)
- John W Castellani
- Thermal and Mountain Medicine Division, U.S. Army Research Institute of Environmental Medicine, Natick, Massachusetts, USA
| | - Michael J Tipton
- Extreme Environments Laboratory, Department of Sport and Exercise Science, University of Portsmouth, Portsmouth, Hampshire, England, United Kingdom
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41
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Taylor NA. Overwhelming Physiological Regulation Through Personal Protection. J Strength Cond Res 2015; 29 Suppl 11:S111-8. [DOI: 10.1519/jsc.0000000000001030] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Ocobock C. The allocation and interaction model: A new model for predicting total energy expenditure of highly active humans in natural environments. Am J Hum Biol 2015; 28:372-80. [DOI: 10.1002/ajhb.22797] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2015] [Revised: 08/30/2015] [Accepted: 09/19/2015] [Indexed: 11/07/2022] Open
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Abstract
Heat stress increases human morbidity and mortality compared to normothermic conditions. Many occupations, disease states, as well as stages of life are especially vulnerable to the stress imposed on the cardiovascular system during exposure to hot ambient conditions. This review focuses on the cardiovascular responses to heat stress that are necessary for heat dissipation. To accomplish this regulatory feat requires complex autonomic nervous system control of the heart and various vascular beds. For example, during heat stress cardiac output increases up to twofold, by increases in heart rate and an active maintenance of stroke volume via increases in inotropy in the presence of decreases in cardiac preload. Baroreflexes retain the ability to regulate blood pressure in many, but not all, heat stress conditions. Central hypovolemia is another cardiovascular challenge brought about by heat stress, which if added to a subsequent central volumetric stress, such as hemorrhage, can be problematic and potentially dangerous, as syncope and cardiovascular collapse may ensue. These combined stresses can compromise blood flow and oxygenation to important tissues such as the brain. It is notable that this compromised condition can occur at cardiac outputs that are adequate during normothermic conditions but are inadequate in heat because of the increased systemic vascular conductance associated with cutaneous vasodilation. Understanding the mechanisms within this complex regulatory system will allow for the development of treatment recommendations and countermeasures to reduce risks during the ever-increasing frequency of severe heat events that are predicted to occur.
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Affiliation(s)
- Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas Marian University College of Osteopathic Medicine, Indianapolis, Indiana
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Smith DL, DeBlois JP, Wharton M, Rowland T. Myocardial functional responses do not contribute to maximal exercise performance in the heat. EXTREME PHYSIOLOGY & MEDICINE 2015; 4:11. [PMID: 26207175 PMCID: PMC4512040 DOI: 10.1186/s13728-015-0031-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/01/2015] [Accepted: 07/14/2015] [Indexed: 11/21/2022]
Abstract
BACKGROUND Both the extent and means by which maximal oxygen uptake ([Formula: see text]) is depressed by elevated ambient temperature are uncertain. Particularly, information is currently unavailable regarding the possible influence of alterations in myocardial function on [Formula: see text] and performance during exercise in the heat. This study investigated the effects of environmental heat on [Formula: see text], peak work capacity, and myocardial function during a standard, progressive cycle test to exhaustion. Twelve euhydrated men (aged 20.7 ± 1.7 years) performed a maximal cycle test in an environmental chamber in both heat stress [35°C, 30% relative humidity (RH)] and temperate (20°C, 30% RH) conditions with measurement of standard gas exchange variables, core temperature, and echocardiographic measures of cardiac function. RESULTS A small but statistically significant reduction of peak work capacity was observed in the heat stress versus temperate conditions (253 ± 30 and 259 ± 30 W, respectively, p = 0.02). Mean [Formula: see text] was not statistically different in the two conditions (p = 0.16) but values were 3.4% lower in the heat, and 9 of 12 participants demonstrated lower values in the heat stress trial. No differences in responses of heart rate, cardiac output, stroke volume, core temperature, hydration status, or myocardial systolic or diastolic function were observed between the two conditions, but perceived body temperature was higher in the heat. CONCLUSIONS The small, negative impact of heat on exercise performance and [Formula: see text] could not be explained by disturbances in myocardial functional responses to exercise in young adult males.
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Affiliation(s)
- Denise L Smith
- />First Responder Health and Safety Laboratory, Department of Health and Exercise Sciences, Skidmore College, Saratoga Springs, NY 12866 USA
| | - Jacob P DeBlois
- />First Responder Health and Safety Laboratory, Department of Health and Exercise Sciences, Skidmore College, Saratoga Springs, NY 12866 USA
| | | | - Thomas Rowland
- />First Responder Health and Safety Laboratory, Department of Health and Exercise Sciences, Skidmore College, Saratoga Springs, NY 12866 USA
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De Blois J, Kjellstrom T, Agewall S, Ezekowitz JA, Armstrong PW, Atar D. The Effects of Climate Change on Cardiac Health. Cardiology 2015; 131:209-17. [DOI: 10.1159/000398787] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2015] [Accepted: 04/08/2015] [Indexed: 11/19/2022]
Abstract
The earth's climate is changing and increasing ambient heat levels are emerging in large areas of the world. An important cause of this change is the anthropogenic emission of greenhouse gases. Climate changes have a variety of negative effects on health, including cardiac health. People with pre-existing medical conditions such as cardiovascular disease (including heart failure), people carrying out physically demanding work and the elderly are particularly vulnerable. This review evaluates the evidence base for the cardiac health consequences of climate conditions, with particular reference to increasing heat exposure, and it also explores the potential further implications.
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46
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The effects of cold and lower body negative pressure on cardiovascular homeostasis. BIOMED RESEARCH INTERNATIONAL 2015; 2015:728145. [PMID: 25866805 PMCID: PMC4383401 DOI: 10.1155/2015/728145] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/15/2014] [Revised: 11/18/2014] [Accepted: 11/20/2014] [Indexed: 11/18/2022]
Abstract
Purpose. The purpose of this study is to determine how cold exposure and lower body negative pressure effected cardiovascular variables. Methods. Eleven males (20.3 years ± 2.7) underwent two 20-minute exposures to LBNP. During the 2 trials, the subjects were exposed to cold air (10°C) (COLD) and to ambient temperature (23°C) (AMB). The trials consisted of a 100-minute pre-LBNP period followed by a 20-minute exposure to LBNP and then a 15-minute recovery period. Cardiovascular variables were recorded every 30 minutes using bioimpedance. Results. When LBNP was applied during the AMB trials, stroke volume immediately decreased. During the COLD trial, there was a five-minute delay before the decrease in stroke volume. Heart rate increased immediately after LBNP initiation during the AMB trials but there was a delay in the increase during the COLD trials. That same pattern was followed with mean arterial blood pressures. Cerebral oxygenation was significantly lower throughout the COLD trial as compared to the AMB trials. Six subjects reported symptoms of syncope or presyncope during the AMB trials but there were no reports of symptoms during the COLD trials. Conclusion. From analysis of this data, cold improved the subject's tolerance to LBNP.
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Gagnon D, Schlader ZJ, Crandall CG. Sympathetic activity during passive heat stress in healthy aged humans. J Physiol 2015; 593:2225-35. [PMID: 25752842 DOI: 10.1113/jp270162] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Accepted: 02/20/2015] [Indexed: 12/31/2022] Open
Abstract
KEY POINTS Cardiovascular adjustments to heat stress are attenuated in healthy aged individuals, which could contribute to their greater prevalence of heat-related illnesses and deaths during heat waves. The attenuated cardiovascular adjustments in the aged could be due to lower increases in sympathetic nerve activity during heat stress. We examined muscle sympathetic nerve activity (MSNA) and plasma catecholamine concentrations in healthy young and aged individuals during whole-body passive heat stress. The main finding of this study is that increases in MSNA and plasma catecholamine concentrations did not differ between young and aged healthy individuals during passive heating. Furthermore, the increase in these variables did not differ when a cold pressor test and lower body negative pressure were superimposed upon heating. These findings suggest that attenuated cardiovascular adjustments to heat stress in healthy aged individuals are unlikely to be related to attenuated increases in sympathetic activity. ABSTRACT Cardiovascular adjustments during heat stress are generally attenuated in healthy aged humans, which could be due to lower increases in sympathetic activity compared to the young. We compared muscle sympathetic nerve activity (MSNA) between 11 young (Y: 28 ± 4 years) and 10 aged (A: 70 ± 5 years) subjects prior to and during passive heating. Furthermore, MSNA responses were compared when a cold pressor test (CPT) and lower body negative pressure (LBNP) were superimposed upon heating. Baseline MSNA burst frequency (Y: 15 ± 4 vs. A: 31 ± 3 bursts min(-1) , P ≤ 0.01) and burst incidence (Y: 26 ± 8 vs. A: 50 ± 7 bursts (100 cardiac cycles (CC))(-1) , P ≤ 0.01) were greater in the aged. Heat stress increased core temperature to a similar extent in both groups (Y: +1.2 ± 0.1 vs. A: +1.2 ± 0.0°C, P = 0.99). Absolute levels of MSNA remained greater in the aged during heat stress (burst frequency: Y: 47 ± 6 vs. A: 63 ± 11 bursts min(-1) , P ≤ 0.01; burst incidence: Y: 48 ± 8 vs. A: 67 ± 9 bursts (100 CC)(-1) , P ≤ 0.01); however, the increase in both variables was similar between groups (both P ≥ 0.1). The CPT and LBNP further increased MSNA burst frequency and burst incidence, although the magnitude of increase was similar between groups (both P ≥ 0.07). These results suggest that increases in sympathetic activity during heat stress are not attenuated in healthy aged humans.
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Affiliation(s)
- Daniel Gagnon
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Centre, Dallas, TX, USA
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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] [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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Abstract
Clinical reports have suggested that patients with heart diseases may be particularly vulnerable to heat injury. This review examines the effects of heat stress on cardiovascular and autonomic functions in patients with chronic heart failure (CHF). Laboratory investigations have shown that cutaneous vasodilator responses to heating are impaired in patients, whereas activation of skin sympathetic nerve activation is not attenuated in CHF as compared to controls. Attenuated cutaneous vasodilation may increase the risk of a heat related illness when CHF subjects are exposed to hyperthermic conditions.
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Secher NH. Inhale your blood volume! Exp Physiol 2014; 99:1285. [DOI: 10.1113/expphysiol.2014.081844] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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