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Caldwell HG, Hoiland RL, Bain AR, Howe CA, Carr JMJR, Gibbons TD, Durrer CG, Tymko MM, Stacey BS, Bailey DM, Sekhon MS, MacLeod DB, Ainslie PN. Evidence for direct CO 2 -mediated alterations in cerebral oxidative metabolism in humans. Acta Physiol (Oxf) 2024; 240:e14197. [PMID: 38958262 DOI: 10.1111/apha.14197] [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: 11/15/2023] [Revised: 06/18/2024] [Accepted: 06/20/2024] [Indexed: 07/04/2024]
Abstract
AIM How the cerebral metabolic rates of oxygen and glucose utilization (CMRO2 and CMRGlc, respectively) are affected by alterations in arterial PCO2 (PaCO2) is equivocal and therefore was the primary question of this study. METHODS This retrospective analysis involved pooled data from four separate studies, involving 41 healthy adults (35 males/6 females). Participants completed stepwise steady-state alterations in PaCO2 ranging between 30 and 60 mmHg. The CMRO2 and CMRGlc were assessed via the Fick approach (CBF × arterial-internal jugular venous difference of oxygen or glucose content, respectively) utilizing duplex ultrasound of the internal carotid artery and vertebral artery to calculate cerebral blood flow (CBF). RESULTS The CMRO2 was altered by 0.5 mL × min-1 (95% CI: -0.6 to -0.3) per mmHg change in PaCO2 (p < 0.001) which corresponded to a 9.8% (95% CI: -13.2 to -6.5) change in CMRO2 with a 9 mmHg change in PaCO2 (inclusive of hypo- and hypercapnia). The CMRGlc was reduced by 7.7% (95% CI: -15.4 to -0.08, p = 0.045; i.e., reduction in net glucose uptake) and the oxidative glucose index (ratio of oxygen to glucose uptake) was reduced by 5.6% (95% CI: -11.2 to 0.06, p = 0.049) with a + 9 mmHg increase in PaCO2. CONCLUSION Collectively, the CMRO2 is altered by approximately 1% per mmHg change in PaCO2. Further, glucose is incompletely oxidized during hypercapnia, indicating reductions in CMRO2 are either met by compensatory increases in nonoxidative glucose metabolism or explained by a reduction in total energy production.
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Affiliation(s)
- Hannah G Caldwell
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Ryan L Hoiland
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
- Department of Anesthesiology, Pharmacology and Therapeutics, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, British Columbia, Canada
- Collaborative Entity for REsearching Brain Ischemia (CEREBRI), University of British Columbia, Vancouver, British Columbia, Canada
| | - Anthony R Bain
- Department of Kinesiology, Faculty of Human Kinetics, University of Windsor, Windsor, Ontario, Canada
| | - Connor A Howe
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Jay M J R Carr
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Travis D Gibbons
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Cody G Durrer
- Centre for Physical Activity Research, Rigshospitalet, Copenhagen, Denmark
| | - Michael M Tymko
- Division of Critical Care Medicine, Department of Medicine, Faculty of Medicine, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada
- Human Cerebrovascular Physiology Laboratory, Department of Human Health and Nutritional Sciences, College of Biological Science, University of Guelph, Guelph, Ontario, Canada
| | - Benjamin S Stacey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Damian M Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Mypinder S Sekhon
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, British Columbia, Canada
- Collaborative Entity for REsearching Brain Ischemia (CEREBRI), University of British Columbia, Vancouver, British Columbia, Canada
- Division of Critical Care Medicine, Department of Medicine, Faculty of Medicine, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada
- Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, British Columbia, Canada
| | - David B MacLeod
- Human Pharmacology and Physiology Lab, Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina, USA
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
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Hao X, Yang Y, Liu J, Zhang D, Ou M, Ke B, Zhu T, Zhou C. The Modulation by Anesthetics and Analgesics of Respiratory Rhythm in the Nervous System. Curr Neuropharmacol 2024; 22:217-240. [PMID: 37563812 PMCID: PMC10788885 DOI: 10.2174/1570159x21666230810110901] [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: 11/23/2022] [Revised: 04/27/2023] [Accepted: 02/28/2023] [Indexed: 08/12/2023] Open
Abstract
Rhythmic eupneic breathing in mammals depends on the coordinated activities of the neural system that sends cranial and spinal motor outputs to respiratory muscles. These outputs modulate lung ventilation and adjust respiratory airflow, which depends on the upper airway patency and ventilatory musculature. Anesthetics are widely used in clinical practice worldwide. In addition to clinically necessary pharmacological effects, respiratory depression is a critical side effect induced by most general anesthetics. Therefore, understanding how general anesthetics modulate the respiratory system is important for the development of safer general anesthetics. Currently used volatile anesthetics and most intravenous anesthetics induce inhibitory effects on respiratory outputs. Various general anesthetics produce differential effects on respiratory characteristics, including the respiratory rate, tidal volume, airway resistance, and ventilatory response. At the cellular and molecular levels, the mechanisms underlying anesthetic-induced breathing depression mainly include modulation of synaptic transmission of ligand-gated ionotropic receptors (e.g., γ-aminobutyric acid, N-methyl-D-aspartate, and nicotinic acetylcholine receptors) and ion channels (e.g., voltage-gated sodium, calcium, and potassium channels, two-pore domain potassium channels, and sodium leak channels), which affect neuronal firing in brainstem respiratory and peripheral chemoreceptor areas. The present review comprehensively summarizes the modulation of the respiratory system by clinically used general anesthetics, including the effects at the molecular, cellular, anatomic, and behavioral levels. Specifically, analgesics, such as opioids, which cause respiratory depression and the "opioid crisis", are discussed. Finally, underlying strategies of respiratory stimulation that target general anesthetics and/or analgesics are summarized.
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Affiliation(s)
- Xuechao Hao
- Department of Anesthesiology, West China Hospital of Sichuan University, Chengdu, 610041, China
| | - Yaoxin Yang
- Department of Anesthesiology, West China Hospital of Sichuan University, Chengdu, 610041, China
- Laboratory of Anesthesia and Critical Care Medicine, National-Local Joint Engineering Research Centre of Translational Medicine of Anesthesiology, West China Hospital of Sichuan University, Chengdu, 610041, China
| | - Jin Liu
- Department of Anesthesiology, West China Hospital of Sichuan University, Chengdu, 610041, China
- Laboratory of Anesthesia and Critical Care Medicine, National-Local Joint Engineering Research Centre of Translational Medicine of Anesthesiology, West China Hospital of Sichuan University, Chengdu, 610041, China
| | - Donghang Zhang
- Department of Anesthesiology, West China Hospital of Sichuan University, Chengdu, 610041, China
- Laboratory of Anesthesia and Critical Care Medicine, National-Local Joint Engineering Research Centre of Translational Medicine of Anesthesiology, West China Hospital of Sichuan University, Chengdu, 610041, China
| | - Mengchan Ou
- Department of Anesthesiology, West China Hospital of Sichuan University, Chengdu, 610041, China
| | - Bowen Ke
- Laboratory of Anesthesia and Critical Care Medicine, National-Local Joint Engineering Research Centre of Translational Medicine of Anesthesiology, West China Hospital of Sichuan University, Chengdu, 610041, China
| | - Tao Zhu
- Department of Anesthesiology, West China Hospital of Sichuan University, Chengdu, 610041, China
| | - Cheng Zhou
- Laboratory of Anesthesia and Critical Care Medicine, National-Local Joint Engineering Research Centre of Translational Medicine of Anesthesiology, West China Hospital of Sichuan University, Chengdu, 610041, China
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Kelly T, Brown C, Bryant-Ekstrand M, Lord R, Dawkins T, Drane A, Futral JE, Barak O, Dragun T, Stembridge M, Spajić B, Drviš I, Duke JW, Ainslie PN, Foster GE, Dujic Z, Lovering AT. Blunted hypoxic pulmonary vasoconstriction in apnoea divers. Exp Physiol 2022; 107:1225-1240. [PMID: 35993480 DOI: 10.1113/ep090326] [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: 01/13/2022] [Accepted: 08/11/2022] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is new and noteworthy? What is the central question of this study? Does the hyperbaric, hypercapnic, acidotic, hypoxic stress of apnoea diving lead to greater pulmonary vasoreactivity and increased right-heart work in apnoea divers? What is the main finding and its importance? Compared to sex- and age-matched controls, Divers had a significantly lower change in total pulmonary resistance in response to short duration isocapnic hypoxia. With oral sildenafil (50 mg), there were no differences in total pulmonary resistance between groups, suggesting Divers can maintain normal pulmonary artery tone in hypoxic conditions. Blunted hypoxic pulmonary vasoconstriction may be beneficial during apnoea diving. ABSTRACT Competitive apnoea divers repetitively dive to depths beyond 50 m. During the final portions of ascent, Divers experience significant hypoxaemia. Additionally, hyperbaria during diving increases thoracic blood volume while simultaneously reducing lung volume, increasing pulmonary artery pressure. We hypothesized that Divers would have exaggerated hypoxic pulmonary vasoconstriction leading to increased right-heart work due to their repetitive hypoxaemia and hyperbaria, and that the administration of sildenafil would have a greater effect in reducing pulmonary resistance in Divers. We recruited 16 Divers and 16 age and sex matched non-diving controls (Controls). Using a double-blinded, placebo-controlled, cross-over design, participants were evaluated for normal cardiac and lung function, then their cardiopulmonary responses to 20-30 minutes of isocapnic hypoxia (end-tidal PO2 = 50 mm Hg) were measured one hour following ingestion of 50 mg sildenafil or placebo. Cardiac structure and cardiopulmonary function were similar at baseline. With placebo, Divers had a significantly smaller increase in total pulmonary resistance than controls after 20-30 minutes isocapnic hypoxia (Δ -3.85 ± 72.85 vs 73.74 ± 91.06 dynes/sec/cm-5 , p = .0222). With sildenafil, Divers and Controls had similarly blunted increases in total pulmonary resistance after 20-30 minutes of hypoxia. Divers also had a significantly lower systemic vascular resistance following sildenafil in normoxia. These data indicate that repetitive apnoea diving leads to a blunted hypoxic pulmonary vasoconstriction. We suggest this is a beneficial adaption allowing for increased cardiac output with reduced right heart work and thus reducing cardiac oxygen utilization under hypoxemic conditions. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Tyler Kelly
- Department of Human Physiology, University of Oregon, Eugene, Oregon, USA
| | - Courtney Brown
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada
| | | | - Rachel Lord
- School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, Wales, UK
| | - Tony Dawkins
- School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, Wales, UK
| | - Aimee Drane
- School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, Wales, UK
| | - Joel E Futral
- Department of Human Physiology, University of Oregon, Eugene, Oregon, USA
| | - Otto Barak
- Department of Physiology, University of Novi Sad, Novi Sad, Serbia
| | - Tanja Dragun
- Department of Integrative Physiology, University of Split School of Medicine, Split, Croatia
| | - Michael Stembridge
- School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, Wales, UK
| | - Boris Spajić
- Faculty of Kinesiology, University of Zagreb, Zagreb, Croatia
| | - Ivan Drviš
- Faculty of Kinesiology, University of Zagreb, Zagreb, Croatia
| | - Joseph W Duke
- Department of Biological Sciences, Northern Arizona University, Flagstaff, Arizona, USA
| | - Philip N Ainslie
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada
| | - Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada
| | - Zeljko Dujic
- Department of Integrative Physiology, University of Split School of Medicine, Split, Croatia
| | - Andrew T Lovering
- Department of Human Physiology, University of Oregon, Eugene, Oregon, USA
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Fernandes LG, Trenhago PR, Feijóo RA, Blanco PJ. Integrated cardiorespiratory system model with short timescale control mechanisms. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2021; 37:e3332. [PMID: 32189436 DOI: 10.1002/cnm.3332] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Revised: 12/26/2019] [Accepted: 02/19/2020] [Indexed: 06/10/2023]
Abstract
A compartmental model of the cardiorespiratory system featuring pulsatile blood flow and gas transport, as well as closed loop mechanisms of cardiorespiratory regulation is presented. Short timescale regulatory action includes baroreflex, peripheral and central chemoreflex feedback. The cardiorespiratory model is composed by compartments to describe blood flow and gas exchange in the major systemic and pulmonic regions. The control systems include formulations to afferent activity of arterial baroreceptor and peripheral and central chemoreceptors. Simulations described here include situations of hypoxia, hypercapnia, and hemorrhage. The overall responses of our simulations agree with physiological (experimental) and theoretical data. Our results suggest that the present model could be used to further understand the interplay among major regulatory mechanisms in the functioning of the cardiovascular and respiratory systems in cases of normal and abnormal physiological conditions.
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Affiliation(s)
- Luciano G Fernandes
- Instituto de Ciências Biológicas e da Saúde, Universidade Federal Rural do Rio de Janeiro, Seropédica, Rio de Janeiro, Brazil
- Instituto Nacional de Ciência e Tecnologia em Medicina Assistida por Computação Científica, Petrópolis, Rio de Janeiro, Brazil
| | - Paulo R Trenhago
- Instituto Nacional de Ciência e Tecnologia em Medicina Assistida por Computação Científica, Petrópolis, Rio de Janeiro, Brazil
- Laboratório Nacional de Computação Científica, Petrópolis, Rio de Janeiro, Brazil
| | - Raúl A Feijóo
- Instituto Nacional de Ciência e Tecnologia em Medicina Assistida por Computação Científica, Petrópolis, Rio de Janeiro, Brazil
- Laboratório Nacional de Computação Científica, Petrópolis, Rio de Janeiro, Brazil
| | - Pablo J Blanco
- Instituto Nacional de Ciência e Tecnologia em Medicina Assistida por Computação Científica, Petrópolis, Rio de Janeiro, Brazil
- Laboratório Nacional de Computação Científica, Petrópolis, Rio de Janeiro, Brazil
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Physiology, pathophysiology and (mal)adaptations to chronic apnoeic training: a state-of-the-art review. Eur J Appl Physiol 2021; 121:1543-1566. [PMID: 33791844 PMCID: PMC8144079 DOI: 10.1007/s00421-021-04664-x] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Accepted: 03/04/2021] [Indexed: 02/08/2023]
Abstract
Breath-hold diving is an activity that humans have engaged in since antiquity to forage for resources, provide sustenance and to support military campaigns. In modern times, breath-hold diving continues to gain popularity and recognition as both a competitive and recreational sport. The continued progression of world records is somewhat remarkable, particularly given the extreme hypoxaemic and hypercapnic conditions, and hydrostatic pressures these athletes endure. However, there is abundant literature to suggest a large inter-individual variation in the apnoeic capabilities that is thus far not fully understood. In this review, we explore developments in apnoea physiology and delineate the traits and mechanisms that potentially underpin this variation. In addition, we sought to highlight the physiological (mal)adaptations associated with consistent breath-hold training. Breath-hold divers (BHDs) are evidenced to exhibit a more pronounced diving-response than non-divers, while elite BHDs (EBHDs) also display beneficial adaptations in both blood and skeletal muscle. Importantly, these physiological characteristics are documented to be primarily influenced by training-induced stimuli. BHDs are exposed to unique physiological and environmental stressors, and as such possess an ability to withstand acute cerebrovascular and neuronal strains. Whether these characteristics are also a result of training-induced adaptations or genetic predisposition is less certain. Although the long-term effects of regular breath-hold diving activity are yet to be holistically established, preliminary evidence has posed considerations for cognitive, neurological, renal and bone health in BHDs. These areas should be explored further in longitudinal studies to more confidently ascertain the long-term health implications of extreme breath-holding activity.
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Busch SA, van Diepen S, Roberts R, Steele AR, Berthelsen LF, Smorschok MP, Bourgoin C, Steinback CD. Short-term hypoxia does not promote arrhythmia during voluntary apnea. Physiol Rep 2021; 9:e14703. [PMID: 33426815 PMCID: PMC7797307 DOI: 10.14814/phy2.14703] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2020] [Accepted: 12/06/2020] [Indexed: 12/19/2022] Open
Abstract
The presence of bradycardic arrhythmias during volitional apnea at altitude may be caused by chemoreflex activation/sensitization. We investigated whether bradyarrhythmic episodes became prevalent in apnea following short‐term hypoxia exposure. Electrocardiograms (ECG; lead II) were collected from 22 low‐altitude residents (F = 12; age=25 ± 5 years) at 671 m. Participants were exposed to normobaric hypoxia (Spo2 ~79 ± 3%) over a 5‐h period. ECG rhythms were assessed during both free‐breathing and maximal volitional end‐expiratory and end‐inspiratory apnea at baseline during normoxia and hypoxia exposure (20 min [AHX]; 5 h [HX5]). Free‐breathing HR became elevated at AHX (78 ± 10 bpm; p < 0.0001) and HX5 (80 ± 12 bpm; p < 0.0001) compared to normoxia (68 ± 10 bpm), whereas apnea caused significant bradycardia at AHX (nadir end‐expiratory −17 ± 14 bpm; p < 0.001) and HX5 (nadir end‐expiratory −19 ± 15 bpm; p < 0.001), but not during normoxia (nadir end‐expiratory −4 ± 13 bpm), with no difference in bradycardia responses between apneas at AHX and HX5. Conduction abnormalities were noted in five participants during normoxia (Premature Ventricular Contraction, Sinus Pause, Junctional Rhythm, Atrial Foci), which remained unchanged during apnea at AHX and HX5 (Premature Ventricular Contraction, Premature Atrial Contraction, Sinus Pause). End‐inspiratory apneas were overall longer across conditions (normoxia p < 0.05; AHX p < 0.01; HX5 p < 0.001), with comparable HR responses to end‐expiratory and fewer occurrences of arrhythmia. While short‐term hypoxia is sufficient to elicit bradycardia during apnea, the occurrence of arrhythmias in response to apnea was not affected. These findings indicate that previously observed bradyarrhythmic events in untrained individuals at altitude only become prevalent following chronic hypoxia specificlly.
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Affiliation(s)
- Stephen A Busch
- Neurovascular Health Laboratory, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Canada
| | - Sean van Diepen
- Department of Critical Care and Divison of Cardiology, Department of Medicine, University of Alberta, Edmonton, Canada
| | - Richard Roberts
- Department of Physiology, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Canada
| | - Andrew R Steele
- Neurovascular Health Laboratory, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Canada
| | - Lindsey F Berthelsen
- Neurovascular Health Laboratory, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Canada
| | - Megan P Smorschok
- Neurovascular Health Laboratory, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Canada
| | - Cody Bourgoin
- Neurovascular Health Laboratory, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Canada
| | - Craig D Steinback
- Neurovascular Health Laboratory, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Canada
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Ott EP, Jacob DW, Baker SE, Holbein WW, Scruggs ZM, Shoemaker JK, Limberg JK. Sympathetic neural recruitment strategies following acute intermittent hypoxia in humans. Am J Physiol Regul Integr Comp Physiol 2020; 318:R961-R971. [PMID: 32267729 DOI: 10.1152/ajpregu.00004.2020] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We examined the effect of acute intermittent hypoxia (IH) on sympathetic neural firing patterns and the role of the carotid chemoreceptors. We hypothesized exposure to acute IH would increase muscle sympathetic nerve activity (MSNA) via an increase in action potential (AP) discharge rates and within-burst firing. We further hypothesized any change in discharge patterns would be attenuated during acute chemoreceptor deactivation (hyperoxia). MSNA (microneurography) was assessed in 17 healthy adults (11 male/6 female; 31 ± 1 yr) during normoxic rest before and after 30 min of experimental IH. Prior to and following IH, participants were exposed to 2 min of 100% oxygen (hyperoxia). AP patterns were studied from the filtered raw MSNA signal using wavelet-based methodology. Compared with baseline, multiunit MSNA burst incidence (P < 0.01), AP incidence (P = 0.01), and AP content per burst (P = 0.01) were increased following IH. There was an increase in the probability of a particular AP cluster firing once (P < 0.01) and more than once (P = 0.03) per burst following IH. There was no effect of hyperoxia on multiunit MSNA at baseline or following IH (P > 0.05); however, hyperoxia following IH attenuated the probability of particular AP clusters firing more than once per burst (P < 0.01). Acute IH increases MSNA by increasing AP discharge rates and within-burst firing. A portion of the increase in within-burst firing following IH can be attributed to the carotid chemoreceptors. These data advance the mechanistic understanding of sympathetic activation following acute IH in humans.
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Affiliation(s)
- Elizabeth P Ott
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - Dain W Jacob
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - Sarah E Baker
- Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota
| | | | | | - J Kevin Shoemaker
- School of Kinesiology, University of Western Ontario, London, Ontario, Canada
| | - Jacqueline K Limberg
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri.,Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota
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Hoiland RL, Fisher JA, Ainslie PN. Regulation of the Cerebral Circulation by Arterial Carbon Dioxide. Compr Physiol 2019; 9:1101-1154. [DOI: 10.1002/cphy.c180021] [Citation(s) in RCA: 101] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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9
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Moir ME, Klassen SA, Al-Khazraji BK, Woehrle E, Smith SO, Matushewski BJ, Kozić D, Dujić Ž, Barak OF, Shoemaker JK. Impaired dynamic cerebral autoregulation in trained breath-hold divers. J Appl Physiol (1985) 2019; 126:1694-1700. [PMID: 31070952 DOI: 10.1152/japplphysiol.00210.2019] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Breath-hold divers (BHD) experience repeated bouts of severe hypoxia and hypercapnia with large increases in blood pressure. However, the impact of long-term breath-hold diving on cerebrovascular control remains poorly understood. The ability of cerebral blood vessels to respond rapidly to changes in blood pressure represents the property of dynamic autoregulation. The current investigation tested the hypothesis that breath-hold diving impairs dynamic autoregulation to a transient hypotensive stimulus. Seventeen BHD (3 women, 11 ± 9 yr of diving) and 15 healthy controls (2 women) completed two or three repeated sit-to-stand trials during spontaneous breathing and poikilocapnic conditions. Heart rate (HR), finger arterial blood pressure (BP), and cerebral blood flow velocity (BFV) from the right middle cerebral artery were measured continuously with three-lead electrocardiography, finger photoplethysmography, and transcranial Doppler ultrasonography, respectively. End-tidal carbon dioxide partial pressure was measured with a gas analyzer. Offline, an index of cerebrovascular resistance (CVRi) was calculated as the quotient of mean BP and BFV. The rate of the drop in CVRi relative to the change in BP provided the rate of regulation [RoR; (∆CVRi/∆T)/∆BP]. The BHD demonstrated slower RoR than controls (P ≤ 0.001, d = 1.4). Underlying the reduced RoR in BHD was a longer time to reach nadir CVRi compared with controls (P = 0.004, d = 1.1). In concert with the longer CVRi response, the time to reach peak BFV following standing was longer in BHD than controls (P = 0.01, d = 0.9). The data suggest impaired dynamic autoregulatory mechanisms to hypotension in BHD. NEW & NOTEWORTHY Impairments in dynamic cerebral autoregulation to hypotension are associated with breath-hold diving. Although weakened autoregulation was observed acutely in this group during apneic stress, we are the first to report on chronic adaptations in cerebral autoregulation. Impaired vasomotor responses underlie the reduced rate of regulation, wherein breath-hold divers demonstrate a prolonged dilatory response to transient hypotension. The slower cerebral vasodilation produces a longer perturbation in cerebral blood flow velocity, increasing the risk of cerebral ischemia.
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Affiliation(s)
- M Erin Moir
- School of Kinesiology, University of Western Ontario , London, Ontario , Canada
| | - Stephen A Klassen
- School of Kinesiology, University of Western Ontario , London, Ontario , Canada
| | - Baraa K Al-Khazraji
- School of Kinesiology, University of Western Ontario , London, Ontario , Canada
| | - Emilie Woehrle
- School of Kinesiology, University of Western Ontario , London, Ontario , Canada
| | - Sydney O Smith
- School of Kinesiology, University of Western Ontario , London, Ontario , Canada
| | - Brad J Matushewski
- School of Kinesiology, University of Western Ontario , London, Ontario , Canada
| | - Duško Kozić
- Faculty of Medicine, University of Novi Sad, Novi Sad, Serbia
| | - Željko Dujić
- Department of Physiology, University of Split School of Medicine , Split , Croatia
| | - Otto F Barak
- Faculty of Medicine, University of Novi Sad, Novi Sad, Serbia.,Faculty of Sports and Physical Education, University of Novi Sad, Novi Sad, Serbia
| | - J Kevin Shoemaker
- School of Kinesiology, University of Western Ontario , London, Ontario , Canada.,Department of Physiology and Pharmacology, University of Western Ontario , London, Ontario , Canada
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10
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Bain AR, Drvis I, Dujic Z, MacLeod DB, Ainslie PN. Physiology of static breath holding in elite apneists. Exp Physiol 2019; 103:635-651. [PMID: 29512224 DOI: 10.1113/ep086269] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Accepted: 03/02/2018] [Indexed: 12/16/2022]
Abstract
NEW FINDINGS What is the topic of this review? This review provides an up-to-date assessment of the physiology involved with extreme static dry-land breath holding in trained apneists. What advances does it highlight? We specifically highlight the recent findings involved with the cardiovascular, cerebrovascular and metabolic function during a maximal breath hold in elite apneists. ABSTRACT Breath-hold-related activities have been performed for centuries, but only recently, within the last ∼30 years, has it emerged as an increasingly popular competitive sport. In apnoea sport, competition relates to underwater distances or simply maximal breath-hold duration, with the current (oxygen-unsupplemented) static breath-hold record at 11 min 35 s. Remarkably, many ultra-elite apneists are able to suppress respiratory urges to the point where consciousness fundamentally limits a breath-hold duration. Here, arterial oxygen saturations as low as ∼50% have been reported. In such cases, oxygen conservation to maintain cerebral functioning is critical, where responses ascribed to the mammalian dive reflex, e.g. sympathetically mediated peripheral vasoconstriction and vagally mediated bradycardia, are central. In defence of maintaining global cerebral oxygen delivery during prolonged breath holds, the cerebral blood flow may increase by ∼100% from resting values. Interestingly, near the termination of prolonged dry static breath holds, recent studies also indicate that reductions in the cerebral oxidative metabolism can occur, probably attributable to the extreme hypercapnia and irrespective of the hypoxaemia. In this review, we highlight and discuss the recent data on the cardiovascular, metabolic and, particularly, cerebrovascular function in competitive apneists performing maximal static breath holds. The physiological adaptation and maladaptation with regular breath-hold training are also summarized, and future research areas in this unique physiological field are highlighted; particularly, the need to determine the potential long-term health impacts of extreme breath holding.
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Affiliation(s)
- Anthony R Bain
- Center for Heart, Lung and Vascular Health, University of British Columbia, Kelowna, BC, Canada.,Integrative Physiology, University of Colorado, Boulder, CO, USA
| | - Ivan Drvis
- Faculty of Kinesiology, University of Zagreb, Zagreb, Croatia
| | - Zeljko Dujic
- Department of Integrative Physiology, University of Split School of Medicine, Split, Croatia
| | - David B MacLeod
- Human Pharmacology and Physiology Laboratory, Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA
| | - Philip N Ainslie
- Center for Heart, Lung and Vascular Health, University of British Columbia, Kelowna, BC, Canada
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Busch SA, Bruce CD, Skow RJ, Pfoh JR, Day TA, Davenport MH, Steinback CD. Mechanisms of sympathetic regulation during Apnea. Physiol Rep 2019; 7:e13991. [PMID: 30693670 PMCID: PMC6349657 DOI: 10.14814/phy2.13991] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2018] [Accepted: 12/26/2018] [Indexed: 12/11/2022] Open
Abstract
Volitional Apnea produces a robust peak sympathetic response through several interacting mechanisms. However, the specific contribution of each mechanism has not been elucidated. Muscle sympathetic activity was collected in participants (n = 10; 24 ± 3 years) that performed four maximal volitional apneas aimed at isolating lung-stretch (mechanical) and chemoreflex drive: (Ainslie and Duffin ) end-expiratory breath-hold, (Ainslie et al. ) end-inspiratory breath-hold, (Alpher et al. ) prehyperventilation breath-hold, and (Andersson and Schagatay ) prehyperoxia breath-hold. A final repeated rebreathe breath-hold protocol was performed to measure the peak sympathetic response during successive breath-holds at increasing chemoreflex stress. Finally, the influence of dynamic ventilation was assessed through asphyxic rebreathe. Muscle sympathetic activity was calculated as the change in burst frequency (burst/min), burst incidence (burst/100 heart-beats), and amplitude (au) between baseline and prevolitional breakpoint. Rebreathe was analyzed at similar chemoreflex stress as inspiratory breath-hold. All maneuvers increased muscle sympathetic activity compared to baseline (P < 0.01). However, prehyperoxia exhibited a smaller increase (+22.18 ± 9.13 burst/min; +25.52 ± 11.7 burst/100 heart-beats) compared to inspiratory, expiratory, and prehyperventilation breath-holds. At similar chemoreflex strain, rebreathe sympathetic activity was blunted compared to inspiratory breath-hold (P < 0.01). Finally, muscle sympathetic activity was not different between the repeated rebreathe trials, despite elevated chemoreflex stress and lower breath-hold duration with each subsequent breath-hold. We have demonstrated an obligatory role of the peripheral, but not central, chemoreflex (prehyperventilation vs. prehyperoxia) in producing peak sympathetic responses. At similar chemoreflex stresses the act of dynamic ventilation, but not static lung stretch per se, blunts muscle sympathetic activity. Finally, similar peak sympathetic responses during successive repeated breath-holds suggest a sympathetic ceiling may exist.
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Affiliation(s)
- Stephen A. Busch
- Neurovascular Health LaboratoryFaculty of Kinesiology, Sport, and RecreationUniversity of AlbertaEdmontonAlbertaCanada
| | - Christina D. Bruce
- Department of BiologyFaculty of Science and TechnologyMount Royal UniversityCalgaryAlbertaCanada
| | - Rachel J. Skow
- Neurovascular Health LaboratoryFaculty of Kinesiology, Sport, and RecreationUniversity of AlbertaEdmontonAlbertaCanada
| | - Jaime R. Pfoh
- Department of BiologyFaculty of Science and TechnologyMount Royal UniversityCalgaryAlbertaCanada
| | - Trevor A. Day
- Department of BiologyFaculty of Science and TechnologyMount Royal UniversityCalgaryAlbertaCanada
| | - Margie H. Davenport
- Neurovascular Health LaboratoryFaculty of Kinesiology, Sport, and RecreationUniversity of AlbertaEdmontonAlbertaCanada
| | - Craig D. Steinback
- Neurovascular Health LaboratoryFaculty of Kinesiology, Sport, and RecreationUniversity of AlbertaEdmontonAlbertaCanada
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12
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Bain AR, Ainslie PN, Hoiland RL, Barak OF, Drvis I, Stembridge M, MacLeod DM, McEneny J, Stacey BS, Tuaillon E, Marchi N, Fayd'Herbe De Maudave A, Dujic Z, MacLeod DB, Bailey DM. Competitive apnea and its effect on the human brain: focus on the redox regulation of blood-brain barrier permeability and neuronal-parenchymal integrity. FASEB J 2018; 32:2305-2314. [PMID: 29191963 DOI: 10.1096/fj.201701031r] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Static apnea provides a unique model that combines transient hypertension, hypercapnia, and severe hypoxemia. With apnea durations exceeding 5 min, the purpose of the present study was to determine how that affects cerebral free-radical formation and the corresponding implications for brain structure and function. Measurements were obtained before and following a maximal apnea in 14 divers with transcerebral exchange kinetics, measured as the product of global cerebral blood flow (duplex ultrasound) and radial arterial to internal jugular venous concentration differences ( a-vD). Apnea increased the systemic (arterial) and, to a greater extent, the regional (jugular venous) concentration of the ascorbate free radical, resulting in a shift from net cerebral uptake to output ( P < 0.05). Peroxidation (lipid hydroperoxides, LDL oxidation), NO bioactivity, and S100β were correspondingly enhanced ( P < 0.05), the latter interpreted as minor and not a pathologic disruption of the blood-brain barrier. However, those changes were insufficient to cause neuronal-parenchymal damage confirmed by the lack of change in the a-vD of neuron-specific enolase and human myelin basic protein ( P > 0.05). Collectively, these observations suggest that increased cerebral oxidative stress following prolonged apnea in trained divers may reflect a functional physiologic response, rather than a purely maladaptive phenomenon.-Bain, A. R., Ainslie, P. N., Hoiland, R. L., Barak, O. F., Drvis, I., Stembridge, M., MacLeod, D. M., McEneny, J., Stacey, B. S., Tuaillon, E., Marchi, N., De Maudave, A. F., Dujic, Z., MacLeod, D. B., Bailey, D. M. Competitive apnea and its effect on the human brain: focus on the redox regulation of blood-brain barrier permeability and neuronal-parenchymal integrity.
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Affiliation(s)
- Anthony R Bain
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, British Columbia, Canada
- Integrative Physiology, University of Colorado, Boulder, Colorado, USA
| | - Philip N Ainslie
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, British Columbia, Canada
| | - Ryan L Hoiland
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, British Columbia, Canada
| | - Otto F Barak
- School of Medicine, University of Split, Split, Croatia
- Faculty of Medicine, University of Novi Sad, Novi Sad, Serbia
| | - Ivan Drvis
- School of Kinesiology, University of Zagreb, Zagreb, Croatia
| | - Mike Stembridge
- Cardiff Centre for Exercise & Health, Cardiff Metropolitan University, Cardiff, United Kingdom
| | | | - Jane McEneny
- Centre for Public Health, Queen's University Belfast, Belfast, Northern Ireland, United Kingdom
| | - Benjamin S Stacey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, United Kingdom
| | - Eduoard Tuaillon
- Unit Mixte de Recherche (UMR), INSERM l'Etablissement Français du Sang (EFS), Université Montpellier 1, Montpellier, France
| | - Nicola Marchi
- UMR, Laboratory of Cerebrovascular Mechanisms of Brain Disorders, Department of Neuroscience, Centre National de la Recherche Scientifique (CNRS), INSERM, Institute of Functional Genomics, Montpellier, France; and
| | - Alexis Fayd'Herbe De Maudave
- UMR, Laboratory of Cerebrovascular Mechanisms of Brain Disorders, Department of Neuroscience, Centre National de la Recherche Scientifique (CNRS), INSERM, Institute of Functional Genomics, Montpellier, France; and
| | - Zeljko Dujic
- School of Medicine, University of Split, Split, Croatia
| | - David B MacLeod
- Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina, USA
| | - Damian M Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, United Kingdom
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13
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Limberg JK, Ott EP, Holbein WW, Baker SE, Curry TB, Nicholson WT, Joyner MJ, Shoemaker JK. Pharmacological assessment of the contribution of the arterial baroreflex to sympathetic discharge patterns in healthy humans. J Neurophysiol 2018; 119:2166-2175. [PMID: 29488839 DOI: 10.1152/jn.00935.2017] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
To study how changes in baroreceptor afferent activity affect patterns of sympathetic neural activation, we manipulated arterial blood pressure with intravenous nitroprusside (NTP) and phenylephrine (PE) and measured action potential (AP) patterns with wavelet-based methodology. We hypothesized that 1) baroreflex unloading (NTP) would increase firing of low-threshold axons and recruitment of latent axons and 2) baroreflex loading (PE) would decrease firing of low-threshold axons. Heart rate (HR, ECG), arterial blood pressure (BP, brachial catheter), and muscle sympathetic nerve activity (MSNA, microneurography of peroneal nerve) were measured at baseline and during steady-state systemic, intravenous NTP (0.5-1.2 µg·kg-1·min-1, n = 13) or PE (0.2-1.0 µg·kg-1·min-1, n = 9) infusion. BP decreased and HR and integrated MSNA increased with NTP ( P < 0.01). AP incidence (326 ± 66 to 579 ± 129 APs/100 heartbeats) and AP content per integrated burst (8 ± 1 to 11 ± 2 APs/burst) increased with NTP ( P < 0.05). The firing probability of low-threshold axons increased with NTP, and recruitment of high-threshold axons was observed (22 ± 3 to 24 ± 3 max cluster number, 9 ± 1 to 11 ± 1 clusters/burst; P < 0.05). BP increased and HR and integrated MSNA decreased with PE ( P < 0.05). PE decreased AP incidence (406 ± 128 to 166 ± 42 APs/100 heartbeats) and resulted in fewer unique clusters (15 ± 2 to 9 ± 1 max cluster number, P < 0.05); components of an integrated burst (APs or clusters per burst) were not altered ( P > 0.05). These data support a hierarchical pattern of sympathetic neural activation during manipulation of baroreceptor afferent activity, with rate coding of active neurons playing the predominant role and recruitment/derecruitment of higher-threshold units occurring with steady-state hypotensive stress. NEW & NOTEWORTHY To study how changes in baroreceptor afferent activity affect patterns of sympathetic neural activation, we manipulated arterial blood pressure with intravenous nitroprusside and phenylephrine and measured sympathetic outflow with wavelet-based methodology. Baroreflex unloading increased sympathetic activity by increasing firing probability of low-threshold axons (rate coding) and recruiting new populations of high-threshold axons. Baroreflex loading decreased sympathetic activity by decreasing the firing probability of larger axons (derecruitment); however, the components of an integrated burst were unaffected.
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Affiliation(s)
- Jacqueline K Limberg
- Department of Nutrition and Exercise Physiology, University of Missouri , Columbia, Missouri.,Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - Elizabeth P Ott
- Department of Nutrition and Exercise Physiology, University of Missouri , Columbia, Missouri
| | - Walter W Holbein
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - Sarah E Baker
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - Timothy B Curry
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - Wayne T Nicholson
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - Michael J Joyner
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - J Kevin Shoemaker
- School of Kinesiology, University of Western Ontario , London, Ontario , Canada
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14
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Bruce CD, Steinback CD, Chauhan UV, Pfoh JR, Abrosimova M, Vanden Berg ER, Skow RJ, Davenport MH, Day TA. Quantifying cerebrovascular reactivity in anterior and posterior cerebral circulations during voluntary breath holding. Exp Physiol 2016; 101:1517-1527. [DOI: 10.1113/ep085764] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2016] [Accepted: 09/05/2016] [Indexed: 12/12/2022]
Affiliation(s)
- Christina D. Bruce
- Department of Biology; Faculty of Science and Technology; Mount Royal University; Calgary Alberta Canada
| | - Craig D. Steinback
- Faculty of Physical Education and Recreation; University of Alberta; Edmonton Alberta Canada
| | - Uday V. Chauhan
- Faculty of Physical Education and Recreation; University of Alberta; Edmonton Alberta Canada
| | - Jamie R. Pfoh
- Department of Biology; Faculty of Science and Technology; Mount Royal University; Calgary Alberta Canada
| | - Maria Abrosimova
- Department of Biology; Faculty of Science and Technology; Mount Royal University; Calgary Alberta Canada
| | - Emily R. Vanden Berg
- Department of Biology; Faculty of Science and Technology; Mount Royal University; Calgary Alberta Canada
- Department of Biology; Faculty of Science; University of Victoria; Victoria BC Canada
| | - Rachel J. Skow
- Faculty of Physical Education and Recreation; University of Alberta; Edmonton Alberta Canada
| | - Margie H. Davenport
- Faculty of Physical Education and Recreation; University of Alberta; Edmonton Alberta Canada
| | - Trevor A. Day
- Department of Biology; Faculty of Science and Technology; Mount Royal University; Calgary Alberta Canada
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15
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Mansukhani MP, Kara T, Caples SM, Somers VK. Chemoreflexes, sleep apnea, and sympathetic dysregulation. Curr Hypertens Rep 2015; 16:476. [PMID: 25097113 DOI: 10.1007/s11906-014-0476-2] [Citation(s) in RCA: 73] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Obstructive sleep apnea (OSA) and hypertension are closely linked conditions. Disordered breathing events in OSA are characterized by increasing efforts against an occluded airway while asleep, resulting in a marked sympathetic response. This is predominantly due to hypoxemia activating the chemoreflexes, resulting in reflex increases in sympathetic neural outflow. In addition, apnea - and the consequent lack of inhibition of the sympathetic system that occurs with lung inflation during normal breathing - potentiates central sympathetic outflow. Sympathetic activation persists into the daytime, and is thought to contribute to hypertension and other adverse cardiovascular outcomes. This review discusses chemoreflex physiology and sympathetic modulation during normal sleep, as well as the sympathetic dysregulation seen in OSA, its extension into wakefulness, and changes after treatment. Evidence supporting the role of the peripheral chemoreflex in the sympathetic dysregulation seen in OSA, including in the context of comorbid obesity, metabolic syndrome, and systemic hypertension, is reviewed. Finally, alterations in cardiovascular variability and other potential mechanisms that may play a role in the autonomic imbalance in OSA are also discussed.
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Affiliation(s)
- Meghna P Mansukhani
- Sleep Medicine, Affiliated Communities Medical Center, 101 Willmar Avenue SW, Willmar, MN, USA,
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Abstract
AbstractElite breath-hold divers are unique athletes challenged with compression induced by hydrostatic pressure and extreme hypoxia/hypercapnia during maximal field dives. The current world records for men are 214 meters for depth (Herbert Nitsch, No-Limits Apnea discipline), 11:35 minutes for duration (Stephane Mifsud, Static Apnea discipline), and 281 meters for distance (Goran Čolak, Dynamic Apnea with Fins discipline). The major physiological adaptations that allow breath-hold divers to achieve such depths and duration are called the “diving response” that is comprised of peripheral vasoconstriction and increased blood pressure, bradycardia, decreased cardiac output, increased cerebral and myocardial blood flow, splenic contraction, and preserved O2 delivery to the brain and heart. This complex of physiological adaptations is not unique to humans, but can be found in all diving mammals. Despite these profound physiological adaptations, divers may frequently show hypoxic loss of consciousness. The breath-hold starts with an easy-going phase in which respiratory muscles are inactive, whereas during the second so-called “struggle” phase, involuntary breathing movements start. These contractions increase cerebral blood flow by facilitating left stroke volume, cardiac output, and arterial pressure. The analysis of the compensatory mechanisms involved in maximal breath-holds can improve brain survival during conditions involving profound brain hypoperfusion and deoxygenation.
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17
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Dujic Z, Breskovic T. Impact of breath holding on cardiovascular respiratory and cerebrovascular health. Sports Med 2012; 42:459-72. [PMID: 22574634 DOI: 10.2165/11599260-000000000-00000] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Human underwater breath-hold diving is a fascinating example of applied environmental physiology. In combination with swimming, it is one of the most popular forms of summer outdoor physical activities. It is performed by a variety of individuals ranging from elite breath-hold divers, underwater hockey and rugby players, synchronized and sprint swimmers, spear fishermen, sponge harvesters and up to recreational swimmers. Very few data currently exist concerning the influence of regular breath holding on possible health risks such as cerebrovascular, cardiovascular and respiratory diseases. A literature search of the PubMed electronic search engine using keywords 'breath-hold diving' and 'apnoea diving' was performed. This review focuses on recent advances in knowledge regarding possibly harmful physiological changes and/or potential health risks associated with breath-hold diving. Available evidence indicates that deep breath-hold dives can be very dangerous and can cause serious acute health problems such a collapse of the lungs, barotrauma at descent and ascent, pulmonary oedema and alveolar haemorrhage, cardiac arrest, blackouts, nitrogen narcosis, decompression sickness and death. Moreover, even shallow apnoea dives, which are far more frequent, can present a significant health risk. The state of affairs is disturbing as athletes, as well as recreational individuals, practice voluntary apnoea on a regular basis. Long-term health risks of frequent maximal breath holds are at present unknown, but should be addressed in future research. Clearly, further studies are needed to better understand the mechanisms related to the possible development or worsening of different clinical disorders in recreational or competitive breath holding and to determine the potential changes in training/competition regimens in order to prevent these adverse events.
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Affiliation(s)
- Zeljko Dujic
- Department of Integrative Physiology, University of Split School of Medicine, Split, Croatia.
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Breskovic T, Steinback CD, Salmanpour A, Shoemaker JK, Dujic Z. Recruitment pattern of sympathetic neurons during breath-holding at different lung volumes in apnea divers and controls. Auton Neurosci 2011; 164:74-81. [PMID: 21641877 DOI: 10.1016/j.autneu.2011.05.003] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2011] [Revised: 05/10/2011] [Accepted: 05/17/2011] [Indexed: 10/18/2022]
Abstract
We tested the hypothesis that breath-hold divers (BHD) attain higher level of sympathetic activation than controls due to the duration of breath-hold rather than a different recruitment strategy. In 6 control subjects and 8 BHD we measured muscle sympathetic neural activity (MSNA) prior to and during functional residual capacity (FRC) and total lung capacity (TLC) breath-holding. On a subset of subjects we applied a new technique for the detection of action potentials (APs) in multiunit MSNA. Compared with controls, BHD group had lower burst AP content (13±7 vs. 6±3AP/burst; P=0.05) and number of active clusters (5±1 vs. 3±1clusters/burst; P=0.05) at baseline. However, the overall sympathetic AP/unit-time was comparable between the groups (131±105 vs. 173±152AP/min; P=0.62) due to increased burst frequency in BHD group (20±4bursts/min) vs. controls (13±3bursts/min) (P=0.039). The achieved level in total MSNA during FRC breath-holds was higher in divers (2298±780 vs. 1484±575a.u./min; P=0.039). Total MSNA at the end of TLC breath-hold was comparable between the groups (157±50 (controls) vs. 214±41s (BHD); P=0.61). FRC and TLC breath-holds increased AP frequency, burst AP content and active clusters/bursts in both groups but the response magnitude was determined by the type of the breath-hold. The divers used fewer number of APs/burst and active clusters/burst. In both groups breath-holds resulted in similar increases in MSNA which were reached both by an increase in firing frequency and by recruitment of previously silent, larger (faster conducting) sympathetic neurons, and possibly by repeated firing within the same burst.
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Affiliation(s)
- Toni Breskovic
- Department of Physiology, University of Split School of Medicine, Soltanska 2, 21000 Split, Croatia
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Steinback CD, Breskovic T, Frances M, Dujic Z, Shoemaker JK. Ventilatory restraint of sympathetic activity during chemoreflex stress. Am J Physiol Regul Integr Comp Physiol 2010; 299:R1407-14. [DOI: 10.1152/ajpregu.00432.2010] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The within-breath modulation of muscle sympathetic nerve activity (MSNA) is well established, with greater activity occurring during expiration and less during inspiration. Whether ventilation per se affects the longer-term (i.e., minute-to-minute) regulation of MSNA has not been determined. We sought to define the specific role of ventilation in regulating sympathetic activation during chemoreflex activation, where both ventilation and MSNA are increased. Ten young healthy subjects performed both asphyxic rebreathing and repeated, rebreathing apneas to cause the same magnitude of chemoreflex stress in the presence or absence of ventilation. Both protocols caused increases in sympathetic burst frequency, burst amplitude, and burst incidence. However, burst frequency was increased more during repeated apneas (12 ± 6 to 25 ± 7 bursts/min) compared with rebreathing (12 ± 5 to 17 ± 7 bursts/min; P < 0.001) due to a greater burst incidence during apneas (36 ± 11 bursts/100 heart beats) vs. rebreathing (26 ± 8 bursts/100 heart beats, P < 0.001). The sympathetic gain to chemoreflex stress was also larger during repeated apneas (2.29 ± 1.29 au/% desaturation) compared with rebreathing (1.44 ± 0.53 au/% desaturation, P < 0.05). The augmented sympathetic response during apneas was associated with a larger pressor response and total peripheral resistance compared with rebreathing. These data demonstrate that ventilation per se restrains sympathetic activation during chemoreflex activation. Further, the augmented sympathetic response during apneas was associated with greater cardiovascular stress and may be relevant to the cardiovascular pathology associated with sleep-disordered breathing.
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Affiliation(s)
- Craig D. Steinback
- Neurovascular Research Laboratory, School of Kinesiology, The University of Western Ontario, London, Ontario, Canada
| | - Toni Breskovic
- Department of Physiology, University of Split School of Medicine, Split, Croatia; and
| | - Maria Frances
- Neurovascular Research Laboratory, School of Kinesiology, The University of Western Ontario, London, Ontario, Canada
| | - Zeljko Dujic
- Department of Physiology, University of Split School of Medicine, Split, Croatia; and
| | - J. Kevin Shoemaker
- Neurovascular Research Laboratory, School of Kinesiology, The University of Western Ontario, London, Ontario, Canada
- Department of Physiology and Pharmacology, The University of Western Ontario, London, Ontario, Canada
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