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Joyner MJ, Wiggins CC, Baker SE, Klassen SA, Senefeld JW. Exercise and Experiments of Nature. Compr Physiol 2023; 13:4879-4907. [PMID: 37358508 PMCID: PMC10853940 DOI: 10.1002/cphy.c220027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/27/2023]
Abstract
In this article, we highlight the contributions of passive experiments that address important exercise-related questions in integrative physiology and medicine. Passive experiments differ from active experiments in that passive experiments involve limited or no active intervention to generate observations and test hypotheses. Experiments of nature and natural experiments are two types of passive experiments. Experiments of nature include research participants with rare genetic or acquired conditions that facilitate exploration of specific physiological mechanisms. In this way, experiments of nature are parallel to classical "knockout" animal models among human research participants. Natural experiments are gleaned from data sets that allow population-based questions to be addressed. An advantage of both types of passive experiments is that more extreme and/or prolonged exposures to physiological and behavioral stimuli are possible in humans. In this article, we discuss a number of key passive experiments that have generated foundational medical knowledge or mechanistic physiological insights related to exercise. Both natural experiments and experiments of nature will be essential to generate and test hypotheses about the limits of human adaptability to stressors like exercise. © 2023 American Physiological Society. Compr Physiol 13:4879-4907, 2023.
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Affiliation(s)
- Michael J Joyner
- Department of Anesthesiology & Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, USA
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
| | - Chad C Wiggins
- Department of Anesthesiology & Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, USA
| | - Sarah E Baker
- Department of Anesthesiology & Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, USA
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
| | - Stephen A Klassen
- Department of Kinesiology, Brock University, St. Catharines, Ontario, Canada
| | - Jonathon W Senefeld
- Department of Anesthesiology & Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, USA
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
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2
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Pruter WW, Klassen SA, Dominelli PB, Wiggins CC, Senefeld JW, Roy TK, Joyner MJ, Baker SE. Attenuated cardiac autonomic function in humans with high-affinity hemoglobin and compensatory polycythemia. Am J Physiol Regul Integr Comp Physiol 2023; 324:R625-R634. [PMID: 36878486 PMCID: PMC10085552 DOI: 10.1152/ajpregu.00113.2022] [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: 05/23/2022] [Revised: 02/28/2023] [Accepted: 03/01/2023] [Indexed: 03/08/2023]
Abstract
During hypoxic exposure, humans with high-affinity hemoglobin (and compensatory polycythemia) have blunted increases in heart rate compared with healthy humans with typical oxyhemoglobin dissociation curves. This response may be associated with altered autonomic control of heart rate. Our hypothesis-generating study aimed to investigate cardiac baroreflex sensitivity and heart rate variability among nine humans with high-affinity hemoglobin [6 females, O2 partial pressure at 50% [Formula: see text] (P50) = 16 ± 1 mmHg] compared with 12 humans with typical affinity hemoglobin (6 F, P50 = 26 ± 1 mmHg). Participants breathed normal room air for a 10-min baseline, followed by 20 min of isocapnic hypoxic exposure, designed to lower the arterial partial pressure O2 ([Formula: see text]) to ∼50 mmHg. Beat-by-beat heart rate and arterial blood pressure were recorded. Data were averaged in 5-min periods throughout the hypoxia exposure, beginning with the last 5 min of baseline in normoxia. Spontaneous cardiac baroreflex sensitivity and heart rate variability were determined using the sequence method and the time and frequency domain analyses, respectively. Cardiac baroreflex sensitivity was lower in humans with high-affinity hemoglobin than controls at baseline and during isocapnic hypoxic exposure (normoxia: 7 ± 4 vs. 16 ± 10 ms/mmHg, hypoxia minutes 15-20: 4 ± 3 vs. 14 ± 11 ms/mmHg; group effect: P = 0.02, high-affinity hemoglobin vs. control, respectively). Heart rate variability calculated in both the time (standard deviation of the N-N interval) and frequency (low frequency) domains was lower in humans with high-affinity hemoglobin than in controls (all P < 0.05). Our data suggest that humans with high-affinity hemoglobin may have attenuated cardiac autonomic function.
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Affiliation(s)
- Wyatt W Pruter
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
| | - Stephen A Klassen
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
- Department of Kinesiology, Brock University, St. Catharines, Ontario, Canada
| | - Paolo B Dominelli
- Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada
| | - Chad C Wiggins
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
| | - Jonathon W Senefeld
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
| | - Tuhin K Roy
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
| | - Michael J Joyner
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
| | - Sarah E Baker
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
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Köhler D, Voshaar T, Stais P, Haidl P, Dellweg D. Hypoxische, anämische und kardial bedingte Hypoxämie: Wann beginnt die Hypoxie im Gewebe? Dtsch Med Wochenschr 2023; 148:475-482. [PMID: 36990120 DOI: 10.1055/a-2007-5450] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/30/2023]
Abstract
ZusammenfassungBei einer Hypoxämie ist oft der Sauerstoffgehalt noch im unteren Normbereich, sodass keine
Hypoxie im Gewebe vorliegt. Wird die Hypoxie-Schwelle im Gewebe bei einer hypoxisch, anämisch
und auch kardial bedingten Hypoxämie erreicht, kommt es im Zellstoffwechsel, unabhängig von
der Genese, zu identischen Gegenregulationen. Im klinischen Alltag wird diese
pathophysiologische Tatsache mitunter ignoriert, obwohl je nach Hypoxämie-Ursache die
Beurteilung und die Therapie stark unterschiedlich sind. Während für die anämische Hypoxämie
restriktive und allgemein akzeptierte Regeln in den Transfusionsrichtlinien festgelegt sind,
wird bei einer hypoxischen Hypoxie früh die Indikation zu einer meist invasiven Beatmung
gestellt. Die klinische Beurteilung und Indikationsstellung fokussiert dabei auf die Parameter
Sauerstoffsättigung, Sauerstoffpartialdruck und Oxygenierungsindex. Während der
Corona-Pandemie sind Fehlinterpretationen der Pathophysiologie sichtbar geworden und haben
vermutlich zu überflüssigen Intubationen geführt. Für die Behandlung einer hypoxischen Hypoxie
mittels invasiver Beatmung aber gibt es keine Evidenz. Im vorliegenden Review wird auf die
Pathophysiologie der verschiedenen Hypoxieursachen unter besonderer Berücksichtigung der
Intubation und Beatmung auf der Intensivstation eingegangen.
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Yang M, Wu Y, Yang XB, Liu T, Zhang Y, Zhuo Y, Luo Y, Zhang N. Establishing a prediction model of severe acute mountain sickness using machine learning of support vector machine recursive feature elimination. Sci Rep 2023; 13:4633. [PMID: 36944699 PMCID: PMC10030784 DOI: 10.1038/s41598-023-31797-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2023] [Accepted: 03/17/2023] [Indexed: 03/23/2023] Open
Abstract
Severe acute mountain sickness (sAMS) can be life-threatening, but little is known about its genetic basis. The study was aimed to explore the genetic susceptibility of sAMS for the purpose of prediction, using microarray data from 112 peripheral blood mononuclear cell (PBMC) samples of 21 subjects, who were exposed to very high altitude (5260 m), low barometric pressure (406 mmHg), and hypobaric hypoxia (VLH) at various timepoints. We found that exposure to VLH activated gene expression in leukocytes, resulting in an inverted CD4/CD8 ratio that interacted with other phenotypic risk factors at the genetic level. A total of 2286 underlying risk genes were input into the support vector machine recursive feature elimination (SVM-RFE) system for machine learning, and a model with satisfactory predictive accuracy and clinical applicability was established for sAMS screening using ten featured genes with significant predictive power. Five featured genes (EPHB3, DIP2B, RHEBL1, GALNT13, and SLC8A2) were identified upstream of hypoxia- and/or inflammation-related pathways mediated by microRNAs as potential biomarkers for sAMS. The established prediction model of sAMS holds promise for clinical application as a genetic screening tool for sAMS.
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Affiliation(s)
- Min Yang
- Department of Traditional Chinese Medicine, Rheumatology Center of Integrated Medicine, The General Hospital of Western Theater Command, PLA, Chengdu, 610083, China.
| | - Yang Wu
- Department of Traditional Chinese Medicine, Rheumatology Center of Integrated Medicine, The General Hospital of Western Theater Command, PLA, Chengdu, 610083, China
| | - Xing-Biao Yang
- Department of Traditional Chinese Medicine, Rheumatology Center of Integrated Medicine, The General Hospital of Western Theater Command, PLA, Chengdu, 610083, China
| | - Tao Liu
- Department of Traditional Chinese Medicine, Rheumatology Center of Integrated Medicine, The General Hospital of Western Theater Command, PLA, Chengdu, 610083, China
| | - Ya Zhang
- Department of Traditional Chinese Medicine, Rheumatology Center of Integrated Medicine, The General Hospital of Western Theater Command, PLA, Chengdu, 610083, China
| | - Yue Zhuo
- Department of Traditional Chinese Medicine, Rheumatology Center of Integrated Medicine, The General Hospital of Western Theater Command, PLA, Chengdu, 610083, China
| | - Yong Luo
- Department of Traditional Chinese Medicine, Rheumatology Center of Integrated Medicine, The General Hospital of Western Theater Command, PLA, Chengdu, 610083, China
| | - Nan Zhang
- Department of Hematology, The General Hospital of Western Theater Command, PLA, Chengdu, 610083, China
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Kato K, Morinaga R, Yokoyama T, Fushuku S, Wakai J, Nakamuta N, Yamamoto Y. Effects of CO 2 on time-dependent changes in cardiorespiratory functions under sustained hypoxia. Respir Physiol Neurobiol 2022; 300:103886. [PMID: 35296417 DOI: 10.1016/j.resp.2022.103886] [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: 10/11/2021] [Revised: 02/16/2022] [Accepted: 03/09/2022] [Indexed: 11/18/2022]
Abstract
Hypercapnia in addition to hypoxia affects the mammalian cardiorespiratory system and has been suggested to exert its effects on cardiorespiratory function by slightly different mechanisms to hypoxia. In the present study, we examined cardiorespiratory changes in urethane-anesthetized rats under hypocapnic (Hypo, 10% O2), isocapnic (Iso, 10% O2 and 4% CO2), and hypercapnic (Hyper, 10% O2 and 8% CO2) hypoxia for 2 h to clarify the effects of CO2 on sustained hypoxia-induced cardiorespiratory responses. Respiratory frequency increased the most in Hypo and tidal volume in Hyper. Minute ventilation, a product of respiratory frequency and tidal volume, increased the most in the latter group. Regarding cardiovascular variables during the hypoxic exposure period, heart rate and mean blood pressure both markedly decreased in Hypo. However, decreases in these parameters were small in Iso, and both increased over the pre-exposure level in Hyper. The present results suggest that CO2 interferes with the hypoxia-activated neural pathway via another pathway under sustained exposure to hypoxia.
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Affiliation(s)
- Kouki Kato
- Center for Laboratory Animal Science, National Defense Medical College, 3-2 Namiki, Tokorozawa, Saitama 359-8513, Japan
| | - Ryosuke Morinaga
- Department of Microscopic Anatomy and Cell Biology, Asahikawa Medical University, 2-1-1-1 Midorigaoka Higashi, Asahikawa, Hokkaido 078-8510, Japan
| | - Takuya Yokoyama
- Department of Anatomy (Cell Biology), Iwate Medical University, 2-1-1 Nishitokuta, Yahaba, Iwate 028-3694, Japan
| | - Seigo Fushuku
- Center for Laboratory Animal Science, National Defense Medical College, 3-2 Namiki, Tokorozawa, Saitama 359-8513, Japan
| | - Jun Wakai
- Department of Laboratory Animal Medicine, Institute for Biomedical Sciences, Iwate Medical University, 2-1-1 Nishitokuta, Yahaba, Iwate 028-3694, Japan
| | - Nobuaki Nakamuta
- Laboratory of Veterinary Anatomy and Cell Biology, Faculty of Agriculture, Iwate University, 18-8, Ueda 3-chome, Morioka, Iwate 020-8550, Japan
| | - Yoshio Yamamoto
- Laboratory of Veterinary Anatomy and Cell Biology, Faculty of Agriculture, Iwate University, 18-8, Ueda 3-chome, Morioka, Iwate 020-8550, Japan.
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Webb KL, Dominelli PB, Baker SE, Klassen SA, Joyner MJ, Senefeld JW, Wiggins CC. Influence of High Hemoglobin-Oxygen Affinity on Humans During Hypoxia. Front Physiol 2022; 12:763933. [PMID: 35095551 PMCID: PMC8795792 DOI: 10.3389/fphys.2021.763933] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2021] [Accepted: 12/22/2021] [Indexed: 01/11/2023] Open
Abstract
Humans elicit a robust series of physiological responses to maintain adequate oxygen delivery during hypoxia, including a transient reduction in hemoglobin-oxygen (Hb-O2) affinity. However, high Hb-O2 affinity has been identified as a beneficial adaptation in several species that have been exposed to high altitude for generations. The observed differences in Hb-O2 affinity between humans and species adapted to high altitude pose a central question: is higher or lower Hb-O2 affinity in humans more advantageous when O2 availability is limited? Humans with genetic mutations in hemoglobin structure resulting in high Hb-O2 affinity have shown attenuated cardiorespiratory adjustments during hypoxia both at rest and during exercise, providing unique insight into this central question. Therefore, the purpose of this review is to examine the influence of high Hb-O2 affinity during hypoxia through comparison of cardiovascular and respiratory adjustments elicited by humans with high Hb-O2 affinity compared to those with normal Hb-O2 affinity.
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Affiliation(s)
- Kevin L. Webb
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, United States
| | | | - Sarah E. Baker
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, United States
| | - Stephen A. Klassen
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, United States
- Department of Kinesiology, Brock University, St. Catharines, ON, Canada
| | - Michael J. Joyner
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, United States
| | - Jonathon W. Senefeld
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, United States
| | - Chad C. Wiggins
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, United States
- *Correspondence: Chad C. Wiggins,
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7
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Stewart GM, Cross TJ, Joyner MJ, Chase SC, Curry T, Lehrer-Graiwer J, Dufu K, Vlahakis NE, Johnson BD. Impact of Pharmacologically Left Shifting the Oxygen-Hemoglobin Dissociation Curve on Arterial Blood Gases and Pulmonary Gas Exchange During Maximal Exercise in Hypoxia. High Alt Med Biol 2021; 22:249-262. [PMID: 34152867 DOI: 10.1089/ham.2020.0159] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Stewart, Glenn M., Troy J. Cross, Michael J. Joyner, Steven C. Chase, Timothy Curry, Josh Lehrer-Graiwer, Kobina Dufu, Nicholas E. Vlahakis, and Bruce D. Johnson. Impact of pharmacologically left shifting the oxygen-hemoglobin dissociation curve on arterial blood gases and pulmonary gas exchange during maximal exercise in hypoxia. High Alt Med Biol. 22:249-262, 2021. Introduction: Physiological and pathological conditions, which reduce the loading of oxygen onto hemoglobin (Hb), can impair exercise capacity and cause debilitating symptoms. Accordingly, this study examined the impact of pharmacologically left shifting the oxygen-hemoglobin dissociation curve (ODC) on arterial oxygen saturation (SaO2) and exercise capacity. Methods: Eight healthy subjects completed a maximal incremental exercise test in hypoxia (FIO2: 0.125) and normoxia (FIO2: 0.21) before (Day 1) and after (Day 15) daily ingestion of 900 mg of voxelotor (an oxygen/Hb affinity modulator). Pulmonary gas exchange and arterial blood gases were assessed throughout exercise and at peak. Data for a 1,500 mg daily drug dose are reported in a limited cohort (n = 3). Results: Fourteen days of drug administration left shifted the ODC (p50 measured under standard conditions, Day 1: 28.0 ± 2.1 mmHg vs. Day 15: 26.1 ± 1.8 mmHg, p < 0.05). Throughout incremental exercise in hypoxia, SaO2 was systematically higher after drug (peak exercise SaO2 on Day 1: 71 ± 2 vs. Day 15: 81% ± 2%, p < 0.001), whereas oxygen extraction (Ca-vO2 diff) and consumption (VO2) were similar (peak exercise Ca-vO2 diff on Day 1: 11.5 ± 1.7 vs. Day 15: 11.0 ± 1.8 ml/100 ml blood, p = 0.417; peak VO2 on Day 1: 2.59 ± 0.39 vs. Day 15: 2.47 ± 0.43 l/min, p = 0.127). Throughout incremental exercise in normoxia, SaO2 was systematically higher after drug, whereas peak VO2 was reduced (peak exercise SaO2 on Day 1: 93.9 ± 1.8 vs. Day 15: 95.8% ± 1.0%, p = 0.008; peak VO2 on Day 1: 3.62 ± 0.55 vs. Day 15: 3.26 ± 52 l/min, p = 0.001). Conclusion: Pharmacologically increasing the affinity of Hb for oxygen improved SaO2 during hypoxia without impacting exercise capacity; however, left shifting the ODC in healthy individuals appears detrimental to exercise capacity in normoxia. Left shifting the ODC to different magnitudes and under more chronic forms of hypoxia warrants further study.
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Affiliation(s)
- Glenn M Stewart
- Human Integrative and Environmental Physiology Laboratory, Department of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota, USA
| | - Troy J Cross
- Human Integrative and Environmental Physiology Laboratory, Department of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota, USA.,Faculty of Medicine and Health, The University of Sydney, Sydney, Australia
| | - Michael J Joyner
- Department of Anesthesia and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, USA
| | - Steven C Chase
- Human Integrative and Environmental Physiology Laboratory, Department of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota, USA
| | - Timothy Curry
- Department of Anesthesia and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, USA
| | | | - Kobina Dufu
- Global Blood Therapeutics, South San Francisco, California, USA
| | | | - Bruce D Johnson
- Human Integrative and Environmental Physiology Laboratory, Department of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota, USA
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Incognito AV, Teixeira AL, Shafer BM, Nardone M, Vermeulen TD, Foster GE, Millar PJ. Muscle sympathetic single-unit responses during rhythmic handgrip exercise and isocapnic hypoxia in males: the role of sympathoexcitation magnitude. J Neurophysiol 2021; 126:170-180. [PMID: 34133241 DOI: 10.1152/jn.00678.2020] [Citation(s) in RCA: 2] [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
A small proportion of postganglionic muscle sympathetic single units can be inhibited during sympathoexcitatory stressors in humans. However, whether these responses are dependent on the specific stressor or the level of sympathoexcitation remains unclear. We hypothesize that, when matched by sympathoexcitatory magnitude, different stressors can evoke similar proportions of inhibited single units. Multiunit and single-unit muscle sympathetic nerve activity (MSNA) were recorded in seven healthy young males at baseline and during 1) rhythmic handgrip exercise (40% of maximum voluntary contraction) and 2) acute isocapnic hypoxia (partial pressure of end-tidal O2 47 ± 3 mmHg). Single units were classified as activated, nonresponsive, or inhibited if the spike frequency was above, within, or below the baseline variability, respectively. By design, rhythmic handgrip and isocapnic hypoxia similarly increased multiunit total MSNA [Δ273 ± 208 vs. Δ254 ± 193 arbitrary units (AU), P = 0.84] and single-unit spike frequency (Δ8 ± 10 vs. Δ12 ± 13 spikes/min, P = 0.12). Among 19 identified single units, the proportions of activated (47% vs. 68%), nonresponsive (32% vs. 16%), and inhibited (21% vs. 16%) single units were not different between rhythmic handgrip and isocapnic hypoxia (P = 0.42). However, only 9 (47%) single units behaved with concordant response patterns across both stressors (7 activated, 1 nonresponsive, and 1 inhibited during both stressors). During the 1-min epoch with the highest increase in total MSNA during hypoxia (Δ595 ± 282 AU, P < 0.01) only one single unit was inhibited. These findings suggest that the proportions of muscle sympathetic single units inhibited during stress are associated with the level of sympathoexcitation and not the stressor per se in healthy young males.NEW & NOTEWORTHY Subpopulations of muscle sympathetic single units can be inhibited during mild sympathoexcitatory stress. We demonstrate that rhythmic handgrip exercise and isocapnic hypoxia, when matched by multiunit sympathoexcitation, induce similar proportions of single-unit inhibition, highlighting that heterogeneous single-unit response patterns are related to the level of sympathoexcitation independent of the stressor type. Interestingly, only 47% of single units behaved with concordant response patterns between stressors, suggesting the potential for functional specificity within the postganglionic neuronal pool.
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Affiliation(s)
- Anthony V Incognito
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - André L Teixeira
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Brooke M Shafer
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| | - Massimo Nardone
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Tyler D Vermeulen
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| | - Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| | - Philip J Millar
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada.,Toronto General Research Institute, Toronto General Hospital, Toronto, Ontario, Canada
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Lear CA, Kasai M, Booth LC, Drury PP, Davidson JO, Maeda Y, Magawa S, Miyagi E, Ikeda T, Westgate JA, Bennet L, Gunn AJ. Peripheral chemoreflex control of fetal heart rate decelerations overwhelms the baroreflex during brief umbilical cord occlusions in fetal sheep. J Physiol 2020; 598:4523-4536. [PMID: 32705685 DOI: 10.1113/jp279573] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Accepted: 07/13/2020] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS The majority of intrapartum decelerations are widely believed to be mediated by the baroreflex secondary to brief umbilical cord occlusions (UCOs) but this remains unproven. We examined the responses to brief-UCOs in fetal sheep and compared these to a phenylephrine-stimulated baroreflex in a separate cohort. A further cohort was instrumented with near-infrared spectroscopy to measure cerebral oxygenation during UCO. The first 3-4 s of the brief-UCOs were consistent with a baroreflex, and associated with a minor fall in fetal heart rate (FHR). Thereafter, the remainder of the FHR decelerations were highly consistent with the peripheral chemoreflex. The baroreflex is not sufficient to produce deep, rapid decelerations characteristic of variable decelerations and it is therefore likely to be a minor contributor to intrapartum decelerations. ABSTRACT Fetal heart rate (FHR) monitoring is widely used to assess fetal wellbeing during labour, yet the physiology underlying FHR patterns remains incompletely understood. The baroreflex is widely believed to mediate brief intrapartum decelerations, but evidence supporting this theory is lacking. We therefore investigated the physiological changes in near-term fetal sheep during brief repeated umbilical cord occlusions (brief-UCOs, n = 15). We compared this to separate cohorts that underwent a phenylephrine challenge to stimulate the baroreflex (n = 9) or were instrumented with near-infrared spectroscopy and underwent prolonged 15-min complete UCO (prolonged-UCO, n = 9). The first 3-4 s of brief-UCOs were associated with hypertension (P = 0.000), a fall in FHR by 9.7-16.9 bpm (P = 0.002). The FHR/MAP relationship during this time was consistent with that observed during a phenylephrine-induced baroreflex. At 4-5 s, the FHR/MAP relationship began to deviate from the phenylephrine baroreflex curve as FHR fell independently of MAP until its nadir in association with intense peripheral vasoconstriction (P = 0.000). During prolonged-UCO, cerebral oxygenation remained steady until 4 s after the start of prolonged-UCO, and then began to fall (P = 0.000). FHR and cerebral oxygenation then fell in parallel until the FHR nadir. In conclusion, the baroreflex has a minor role in mediating the first 3-4 s of FHR decelerations during complete UCO, but thereafter the peripheral chemoreflex is the dominant mediator. Overall, the baroreflex is neither necessary nor sufficient to produce deep, rapid decelerations characteristic of variable decelerations; it is therefore likely to be a minor contributor to intrapartum decelerations.
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Affiliation(s)
- Christopher A Lear
- Fetal Physiology and Neuroscience Group, Department of Physiology, The University of Auckland, Auckland, New Zealand
| | - Michi Kasai
- Fetal Physiology and Neuroscience Group, Department of Physiology, The University of Auckland, Auckland, New Zealand.,Department of Obstetrics and Gynecology, Yokohama City University, Yokohama, Japan
| | - Lindsea C Booth
- Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia
| | - Paul P Drury
- Fetal Physiology and Neuroscience Group, Department of Physiology, The University of Auckland, Auckland, New Zealand
| | - Joanne O Davidson
- Fetal Physiology and Neuroscience Group, Department of Physiology, The University of Auckland, Auckland, New Zealand
| | - Yoshiki Maeda
- Fetal Physiology and Neuroscience Group, Department of Physiology, The University of Auckland, Auckland, New Zealand.,Department of Obstetrics and Gynecology, Mie University, Mie, Japan
| | - Shoichi Magawa
- Fetal Physiology and Neuroscience Group, Department of Physiology, The University of Auckland, Auckland, New Zealand.,Department of Obstetrics and Gynecology, Mie University, Mie, Japan
| | - Etsuko Miyagi
- Department of Obstetrics and Gynecology, Yokohama City University, Yokohama, Japan
| | - Tomoaki Ikeda
- Department of Obstetrics and Gynecology, Mie University, Mie, Japan
| | - Jenny A Westgate
- Fetal Physiology and Neuroscience Group, Department of Physiology, The University of Auckland, Auckland, New Zealand
| | - Laura Bennet
- Fetal Physiology and Neuroscience Group, Department of Physiology, The University of Auckland, Auckland, New Zealand
| | - Alistair J Gunn
- Fetal Physiology and Neuroscience Group, Department of Physiology, The University of Auckland, Auckland, New Zealand
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10
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Stewart GM, Chase S, Cross TJ, Wheatley-Guy CM, Joyner MJ, Curry T, Lehrer-Graiwer J, Dufu K, Vlahakis NE, Johnson BD. Effects of an allosteric hemoglobin affinity modulator on arterial blood gases and cardiopulmonary responses during normoxic and hypoxic low-intensity exercise. J Appl Physiol (1985) 2020; 128:1467-1476. [PMID: 32324473 DOI: 10.1152/japplphysiol.00185.2019] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Numerous pathophysiological conditions induce hypoxemia-related cardiopulmonary perturbations, decrements in exercise capacity, and debilitating symptoms. Accordingly, this study investigated the efficacy of an allosteric hemoglobin modulator (voxelotor) to enhance arterial oxygen saturation during low-intensity exercise in hypoxia. Eight normal healthy subjects (36 ± 7 yr; 73.8 ± 9.5 kg; 3 women) completed a submaximal cycling test (60 W) under normoxic ([Formula: see text]: 0.21; O2 partial pressure: 144 mmHg) and hypoxic ([Formula: see text]: 0.125; O2 partial pressure: 82 mmHg) conditions before (day 1) and after (day 15) 14 days of oral drug administration. While stationary on a cycle ergometer and during exercise, ratings of perceived exertion (RPE) and dyspnea, oxygen consumption (V̇o2), and cardiac output (Q) were measured noninvasively, while arterial blood pressure (MAP) and blood gases ([Formula: see text], [Formula: see text], and [Formula: see text]) were measured invasively. The 14-day drug administration left shifted the oxygen-hemoglobin dissociation curve (ODC; p50 measured at standard pH and Pco2; day 1: 28.0 ± 2.1 mmHg vs. day 15: 26.1 ± 1.8 mmHg, P < 0.05). RPE, dyspnea, V̇o2, Q, and MAP were not different between day 1 and day 15. [Formula: see text] was similar during normoxia on day 1 and day 15 while stationary but higher during exercise (day 1: 95.2 ± 0.4% vs. day 15: 96.6 ± 0.3%, P < 0.05). [Formula: see text] was higher during hypoxia on day 15 while stationary (day 1: 82.9 ± 3.4% vs. day 15: 90.9 ± 1.8%, P < 0.05) and during exercise (day 1: 73.6 ± 2.5% vs. day 15: 84.8 ± 2.7%, P < 0.01). [Formula: see text] and [Formula: see text]were systematically higher and lower, respectively, after drug (P < 0.01), while the alveolar-arterial oxygen difference was unchanged suggesting hyperventilation contributed to the rise in [Formula: see text]. Oral administration of voxelotor left shifted the ODC and stimulated a mild hyperventilation, leading to improved arterial oxygen saturation without altering V̇o2 and central hemodynamics during rest and low-intensity exercise. This effect was more pronounced during submaximal hypoxic exercise, when arterial desaturation was more evident. Additional studies are needed to determine the effects of voxelotor during maximal exercise and under chronic forms of hypoxia.NEW & NOTEWORTHY In humans, a novel allosteric hemoglobin-oxygen affinity modulator was administered to comprehensively examine the cardiopulmonary consequences of stabilizing a portion of the available hemoglobin in a high-oxygen affinity state during submaximal exercise in normoxia and hypoxia. Oral administration of voxelotor enhanced arterial oxygen saturation during submaximal exercise without altering oxygen consumption and central hemodynamics; however, the partial pressure of arterial carbon dioxide was reduced and the partial pressure of arterial oxygen was increased implying that hyperventilation also contributed to the increase in oxygen saturation. The preservation of arterial oxygen saturation and content was particularly evident during hypoxic submaximal exercise, when arterial desaturation typically occurs, but this did not influence arterial-venous oxygen difference.
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Affiliation(s)
- Glenn M Stewart
- Human Integrative and Environmental Physiology Laboratory, Department of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota
| | - Steven Chase
- Human Integrative and Environmental Physiology Laboratory, Department of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota
| | - Troy J Cross
- Human Integrative and Environmental Physiology Laboratory, Department of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota
| | - Courtney M Wheatley-Guy
- Human Integrative and Environmental Physiology Laboratory, Department of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota
| | - Michael J Joyner
- Department of Anesthesia and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
| | - Timothy Curry
- Department of Anesthesia and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
| | | | - Kobina Dufu
- Global Blood Therapeutics, South San Francisco, California
| | | | - Bruce D Johnson
- Human Integrative and Environmental Physiology Laboratory, Department of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota
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Dominelli PB, Wiggins CC, Baker SE, Shepherd JRA, Roberts SK, Roy TK, Curry TB, Hoyer JD, Oliveira JL, Joyner MJ. Influence of high affinity haemoglobin on the response to normoxic and hypoxic exercise. J Physiol 2020; 598:1475-1490. [PMID: 31923331 DOI: 10.1113/jp279161] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2019] [Accepted: 12/20/2019] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Theoretical models suggest there is no benefit of high affinity haemoglobin to preserve maximal oxygen uptake in acute hypoxia but the comparative biology literature has many examples of species that are evolutionarily adapted to hypoxia and have high affinity haemoglobin. We studied humans with high affinity haemoglobin and compensatory polycythaemia. These subjects performed maximal exercise tests in normoxia and hypoxia to determine how their altered haemoglobin affinity impacts hypoxic exercise tolerance. The high affinity haemoglobin participants demonstrated an attenuated decline in maximal aerobic capacity in acute hypoxia. Those with high affinity haemoglobin had no worsening of pulmonary gas exchange during hypoxic exercise but had greater lactate and lower pH than controls for all exercise bouts. High affinity haemoglobin and compensatory polycythaemia mitigated the decline in exercise performance in acute hypoxia through a higher arterial oxygen content and an unchanged pulmonary gas exchange. ABSTRACT The longstanding dogma is that humans exhibit an acute reduction in haemoglobin (Hb) binding affinity for oxygen that facilitates adaptation to moderate hypoxia. However, many animals have adapted to high altitude through enhanced Hb binding affinity for oxygen. The objective of the study was to determine whether high affinity haemoglobin (HAH) affects maximal and submaximal exercise capacity. To accomplish this, we recruited individuals (n = 11, n = 8 females) with HAH (P50 = 16 ± 1 mmHg), had them perform normoxic and acute hypoxic (15% inspired oxygen) maximal exercise tests, and then compared their results to matched controls (P50 = 26 ± 1, n = 14, n = 8 females). Cardiorespiratory and arterial blood gases were collected throughout both exercise tests. Despite no difference in end-exercise arterial oxygen tension in hypoxia (59 ± 6 vs. 59 ± 9 mmHg for controls and HAH, respectively), the HAH subjects' oxyhaemoglobin saturation ( S a , O 2 ) was ∼7% higher. Those with HAH had an attenuated decline in maximal oxygen uptake ( V ̇ O 2 max ) (4 ± 5% vs. 12 ± %, p < 0.001) in hypoxia and the change in V ̇ O 2 max between trials was related to the change in S a O 2 (r = -0.75, p < 0.0001). Compared to normoxia, the controls' alveolar-to-arterial oxygen gradient significantly increased during hypoxic exercise, whereas pulmonary gas exchange in HAH subjects was unchanged between the two exercise trials. However, arterial lactate was significantly higher and arterial pH significantly lower in the HAH subjects for both exercise trials. We conclude that HAH attenuates the decline in maximal aerobic capacity and preserves pulmonary gas exchange during acute hypoxic exercise. Our data support the comparative biology literature indicating that HAH is a positive adaptation to acute hypoxia.
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Affiliation(s)
- Paolo B Dominelli
- Department of Kinesiology, University of Waterloo, Waterloo, ON, Canada.,Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, USA
| | - Chad C Wiggins
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, USA
| | - Sarah E Baker
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, USA
| | - John R A Shepherd
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, USA
| | - Shelly K Roberts
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, USA
| | - Tuhin K Roy
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, USA
| | - Timothy B Curry
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, USA
| | - James D Hoyer
- Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN, USA
| | - Jennifer L Oliveira
- Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN, USA
| | - Michael J Joyner
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, USA
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