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Ruggiero L, Harrison SWD, Rice CL, McNeil CJ. Neuromuscular fatigability at high altitude: Lowlanders with acute and chronic exposure, and native highlanders. Acta Physiol (Oxf) 2022; 234:e13788. [PMID: 35007386 PMCID: PMC9286620 DOI: 10.1111/apha.13788] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2021] [Revised: 01/04/2022] [Accepted: 01/05/2022] [Indexed: 01/18/2023]
Abstract
Ascent to high altitude is accompanied by a reduction in partial pressure of inspired oxygen, which leads to interconnected adjustments within the neuromuscular system. This review describes the unique challenge that such an environment poses to neuromuscular fatigability (peripheral, central and supraspinal) for individuals who normally reside near to sea level (SL) (<1000 m; ie, lowlanders) and for native highlanders, who represent the manifestation of high altitude-related heritable adaptations across millennia. Firstly, the effect of acute exposure to high altitude-related hypoxia on neuromuscular fatigability will be examined. Under these conditions, both supraspinal and peripheral fatigability are increased compared with SL. The specific mechanisms contributing to impaired performance are dependent on the exercise paradigm and amount of muscle mass involved. Next, the effect of chronic exposure to high altitude (ie, acclimatization of ~7-28 days) will be considered. With acclimatization, supraspinal fatigability is restored to SL values, regardless of the amount of muscle mass involved, whereas peripheral fatigability remains greater than SL except when exercise involves a small amount of muscle mass (eg, knee extensors). Indeed, when whole-body exercise is involved, peripheral fatigability is not different to acute high-altitude exposure, due to competing positive (haematological and muscle metabolic) and negative (respiratory-mediated) effects of acclimatization on neuromuscular performance. In the final section, we consider evolutionary adaptations of native highlanders (primarily Himalayans of Tibet and Nepal) that may account for their superior performance at altitude and lesser degree of neuromuscular fatigability compared with acclimatized lowlanders, for both single-joint and whole-body exercise.
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Affiliation(s)
- Luca Ruggiero
- Laboratory of Physiomechanics of Locomotion Department of Pathophysiology and Transplantation University of Milan Milan Italy
| | - Scott W. D. Harrison
- School of Kinesiology Faculty of Health Sciences The University of Western Ontario London Ontario Canada
| | - Charles L. Rice
- School of Kinesiology Faculty of Health Sciences The University of Western Ontario London Ontario Canada
- Department of Anatomy and Cell Biology Schulich School of Medicine and Dentistry The University of Western Ontario London Ontario Canada
| | - Chris J. McNeil
- Centre for Heart, Lung & Vascular Health School of Health and Exercise Sciences University of British Columbia Kelowna British Columbia Canada
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Pamenter ME, Powell FL. Time Domains of the Hypoxic Ventilatory Response and Their Molecular Basis. Compr Physiol 2016; 6:1345-85. [PMID: 27347896 DOI: 10.1002/cphy.c150026] [Citation(s) in RCA: 84] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Ventilatory responses to hypoxia vary widely depending on the pattern and length of hypoxic exposure. Acute, prolonged, or intermittent hypoxic episodes can increase or decrease breathing for seconds to years, both during the hypoxic stimulus, and also after its removal. These myriad effects are the result of a complicated web of molecular interactions that underlie plasticity in the respiratory control reflex circuits and ultimately control the physiology of breathing in hypoxia. Since the time domains of the physiological hypoxic ventilatory response (HVR) were identified, considerable research effort has gone toward elucidating the underlying molecular mechanisms that mediate these varied responses. This research has begun to describe complicated and plastic interactions in the relay circuits between the peripheral chemoreceptors and the ventilatory control circuits within the central nervous system. Intriguingly, many of these molecular pathways seem to share key components between the different time domains, suggesting that varied physiological HVRs are the result of specific modifications to overlapping pathways. This review highlights what has been discovered regarding the cell and molecular level control of the time domains of the HVR, and highlights key areas where further research is required. Understanding the molecular control of ventilation in hypoxia has important implications for basic physiology and is emerging as an important component of several clinical fields. © 2016 American Physiological Society. Compr Physiol 6:1345-1385, 2016.
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Affiliation(s)
| | - Frank L Powell
- Physiology Division, Department of Medicine, University of California San Diego, La Jolla, California, USA
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Fatemian M, Herigstad M, Croft QPP, Formenti F, Cardenas R, Wheeler C, Smith TG, Friedmannova M, Dorrington KL, Robbins PA. Determinants of ventilation and pulmonary artery pressure during early acclimatization to hypoxia in humans. J Physiol 2016; 594:1197-213. [PMID: 25907672 PMCID: PMC4771781 DOI: 10.1113/jp270061] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2014] [Accepted: 04/14/2015] [Indexed: 12/11/2022] Open
Abstract
Pulmonary ventilation and pulmonary arterial pressure both rise progressively during the first few hours of human acclimatization to hypoxia. These responses are highly variable between individuals, but the origin of this variability is unknown. Here, we sought to determine whether the variabilities between different measures of response to sustained hypoxia were related, which would suggest a common source of variability. Eighty volunteers individually underwent an 8-h isocapnic exposure to hypoxia (end-tidal P(O2)=55 Torr) in a purpose-built chamber. Measurements of ventilation and pulmonary artery systolic pressure (PASP) assessed by Doppler echocardiography were made during the exposure. Before and after the exposure, measurements were made of the ventilatory sensitivities to acute isocapnic hypoxia (G(pO2)) and hyperoxic hypercapnia, the latter divided into peripheral (G(pCO2)) and central (G(cCO2)) components. Substantial acclimatization was observed in both ventilation and PASP, the latter being 40% greater in women than men. No correlation was found between the magnitudes of pulmonary ventilatory and pulmonary vascular responses. For G(pO2), G(pCO2) and G(cC O2), but not the sensitivity of PASP to acute hypoxia, the magnitude of the increase during acclimatization was proportional to the pre-acclimatization value. Additionally, the change in G(pO2) during acclimatization to hypoxia correlated well with most other measures of ventilatory acclimatization. Of the initial measurements prior to sustained hypoxia, only G(pCO2) predicted the subsequent rise in ventilation and change in G(pO2) during acclimatization. We conclude that the magnitudes of the ventilatory and pulmonary vascular responses to sustained hypoxia are predominantly determined by different factors and that the initial G(pCO2) is a modest predictor of ventilatory acclimatization.
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Affiliation(s)
- Marzieh Fatemian
- Department of Physiology, Anatomy and Genetics, University of Oxford, Sherrington Building, Parks Road, Oxford, OX1 3PT, UK
| | - Mari Herigstad
- Department of Physiology, Anatomy and Genetics, University of Oxford, Sherrington Building, Parks Road, Oxford, OX1 3PT, UK
| | - Quentin P P Croft
- Department of Physiology, Anatomy and Genetics, University of Oxford, Sherrington Building, Parks Road, Oxford, OX1 3PT, UK
| | - Federico Formenti
- Department of Physiology, Anatomy and Genetics, University of Oxford, Sherrington Building, Parks Road, Oxford, OX1 3PT, UK
| | - Rosa Cardenas
- Department of Physiology, Anatomy and Genetics, University of Oxford, Sherrington Building, Parks Road, Oxford, OX1 3PT, UK
| | - Carly Wheeler
- Department of Physiology, Anatomy and Genetics, University of Oxford, Sherrington Building, Parks Road, Oxford, OX1 3PT, UK
| | - Thomas G Smith
- Department of Physiology, Anatomy and Genetics, University of Oxford, Sherrington Building, Parks Road, Oxford, OX1 3PT, UK
| | - Maria Friedmannova
- Department of Physiology, Anatomy and Genetics, University of Oxford, Sherrington Building, Parks Road, Oxford, OX1 3PT, UK
| | - Keith L Dorrington
- Department of Physiology, Anatomy and Genetics, University of Oxford, Sherrington Building, Parks Road, Oxford, OX1 3PT, UK
| | - Peter A Robbins
- Department of Physiology, Anatomy and Genetics, University of Oxford, Sherrington Building, Parks Road, Oxford, OX1 3PT, UK
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Fan JL, Subudhi AW, Duffin J, Lovering AT, Roach RC, Kayser B. AltitudeOmics: Resetting of Cerebrovascular CO2 Reactivity Following Acclimatization to High Altitude. Front Physiol 2016; 6:394. [PMID: 26779030 PMCID: PMC4705915 DOI: 10.3389/fphys.2015.00394] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Accepted: 12/03/2015] [Indexed: 12/25/2022] Open
Abstract
Previous studies reported enhanced cerebrovascular CO2 reactivity upon ascent to high altitude using linear models. However, there is evidence that this response may be sigmoidal in nature. Moreover, it was speculated that these changes at high altitude are mediated by alterations in acid-base buffering. Accordingly, we reanalyzed previously published data to assess middle cerebral blood flow velocity (MCAv) responses to modified rebreathing at sea level (SL), upon ascent (ALT1) and following 16 days of acclimatization (ALT16) to 5260 m in 21 lowlanders. Using sigmoid curve fitting of the MCAv responses to CO2, we found the amplitude (95 vs. 129%, SL vs. ALT1, 95% confidence intervals (CI) [77, 112], [111, 145], respectively, P = 0.024) and the slope of the sigmoid response (4.5 vs. 7.5%/mmHg, SL vs. ALT1, 95% CIs [3.1, 5.9], [6.0, 9.0], respectively, P = 0.026) to be enhanced at ALT1, which persisted with acclimatization at ALT16 (amplitude: 177, 95% CI [139, 215], P < 0.001; slope: 10.3%/mmHg, 95% CI [8.2, 12.5], P = 0.003) compared to SL. Meanwhile, the sigmoidal response midpoint was unchanged at ALT1 (SL: 36.5 mmHg; ALT1: 35.4 mmHg, 95% CIs [34.0, 39.0], [33.1, 37.7], respectively, P = 0.982), while it was reduced by ~7 mmHg at ALT16 (28.6 mmHg, 95% CI [26.4, 30.8], P = 0.001 vs. SL), indicating leftward shift of the cerebrovascular CO2 response to a lower arterial partial pressure of CO2 (PaCO2) following acclimatization to altitude. Sigmoid fitting revealed a leftward shift in the midpoint of the cerebrovascular response curve which could not be observed with linear fitting. These findings demonstrate that there is resetting of the cerebrovascular CO2 reactivity operating point to a lower PaCO2 following acclimatization to high altitude. This cerebrovascular resetting is likely the result of an altered acid-base buffer status resulting from prolonged exposure to the severe hypocapnia associated with ventilatory acclimatization to high altitude.
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Affiliation(s)
- Jui-Lin Fan
- Centre for Translational Physiology, University of OtagoWellington, New Zealand; Department of Surgery and Anaesthesia, University of OtagoWellington, New Zealand
| | - Andrew W Subudhi
- Department of Emergency Medicine, Altitude Research Center, University of Colorado DenverAurora, CO, USA; Department of Biology, University of Colorado Colorado SpringsColorado Springs, CO, USA
| | - James Duffin
- Department of Physiology, University of TorontoToronto, ON, Canada; Department of Anaesthesiology, University of TorontoToronto, ON, Canada; University Health NetworkToronto, ON, Canada
| | - Andrew T Lovering
- Department of Human Physiology, University of Oregon Eugene, Oregon, OR, USA
| | - Robert C Roach
- Department of Emergency Medicine, Altitude Research Center, University of Colorado DenverAurora, CO, USA; Department of Biology, University of Colorado Colorado SpringsColorado Springs, CO, USA
| | - Bengt Kayser
- Institute of Sports Sciences, Faculty of Biology and Medicine, University of LausanneLausanne, Switzerland; Department of Physiology, Faculty of Biology and Medicine, University of LausanneLausanne, Switzerland
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Teppema LJ, Dahan A. The Ventilatory Response to Hypoxia in Mammals: Mechanisms, Measurement, and Analysis. Physiol Rev 2010; 90:675-754. [DOI: 10.1152/physrev.00012.2009] [Citation(s) in RCA: 257] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The respiratory response to hypoxia in mammals develops from an inhibition of breathing movements in utero into a sustained increase in ventilation in the adult. This ventilatory response to hypoxia (HVR) in mammals is the subject of this review. The period immediately after birth contains a critical time window in which environmental factors can cause long-term changes in the structural and functional properties of the respiratory system, resulting in an altered HVR phenotype. Both neonatal chronic and chronic intermittent hypoxia, but also chronic hyperoxia, can induce such plastic changes, the nature of which depends on the time pattern and duration of the exposure (acute or chronic, episodic or not, etc.). At adult age, exposure to chronic hypoxic paradigms induces adjustments in the HVR that seem reversible when the respiratory system is fully matured. These changes are orchestrated by transcription factors of which hypoxia-inducible factor 1 has been identified as the master regulator. We discuss the mechanisms underlying the HVR and its adaptations to chronic changes in ambient oxygen concentration, with emphasis on the carotid bodies that contain oxygen sensors and initiate the response, and on the contribution of central neurotransmitters and brain stem regions. We also briefly summarize the techniques used in small animals and in humans to measure the HVR and discuss the specific difficulties encountered in its measurement and analysis.
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Affiliation(s)
- Luc J. Teppema
- Department of Anesthesiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Albert Dahan
- Department of Anesthesiology, Leiden University Medical Center, Leiden, The Netherlands
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Herigstad M, Fatemian M, Robbins PA. Respiratory control during air-breathing exercise in humans following an 8 h exposure to hypoxia. Respir Physiol Neurobiol 2008; 162:169-75. [PMID: 18602500 PMCID: PMC3764425 DOI: 10.1016/j.resp.2008.06.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2008] [Revised: 04/25/2008] [Accepted: 06/03/2008] [Indexed: 11/23/2022]
Abstract
Hypoxic exposure lasting a few hours results in an elevation of ventilation and a lowering of end-tidal PCO2(PETCO2) that persists on return to breathing air. We sought to determine whether this increment in ventilation is fixed (hypothesis 1), or whether it increases in proportion to the rise in metabolic rate associated with exercise (hypothesis 2). Ten subjects were studied on two separate days. On 1 day, subjects were exposed to 8 h of isocapnic hypoxia (end-tidal PO2 55 Torr) and on the other day to 8 h of euoxia as a control. Before and 30 min after each exposure, subjects undertook an incremental exercise test. The best fit of a model for the variation in PETCO2 with metabolic rate gave a residual squared error that was ∼20-fold less for hypothesis 2 than for hypothesis 1 (p < 0.005, F-ratio test). We conclude that the alterations in respiratory control induced during early ventilatory acclimatization to hypoxia better reflect those associated with hypothesis 2 rather than hypothesis 1.
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Affiliation(s)
- Mari Herigstad
- Department of Physiology, Anatomy and Genetics, Parks Road, University of Oxford, Oxford OX1 3PT, United Kingdom
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8
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Robbins PA. Role of the peripheral chemoreflex in the early stages of ventilatory acclimatization to altitude. Respir Physiol Neurobiol 2007; 158:237-42. [PMID: 17434348 DOI: 10.1016/j.resp.2007.03.008] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2006] [Revised: 03/09/2007] [Accepted: 03/11/2007] [Indexed: 11/22/2022]
Abstract
This review of ventilatory acclimatization to altitude/hypoxia (VAH) emphasizes the widely differing timescales that VAH is considered to encompass. The review concludes: (1) that early (24-48h) VAH is unlikely to arise as a reaction to the respiratory alkalosis that is normally associated with exposure to hypoxia; (2) that changes in peripheral chemoreflex function may be sufficiently rapid to explain early VAH; (3) that alterations in gene expression induced by hypoxia through the hypoxia-inducible factor (HIF) signalling pathway may underlie a major component of VAH; and (4) that compensatory adjustments to acid-base balance in response to the initial respiratory alkalosis may have more significance for the slower changes observed later in VAH.
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Affiliation(s)
- Peter A Robbins
- Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford OX1 3PT, UK.
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Alea OA, Czapla MA, Lasky JA, Simakajornboon N, Gozal E, Gozal D. PDGF-beta receptor expression and ventilatory acclimatization to hypoxia in the rat. Am J Physiol Regul Integr Comp Physiol 2000; 279:R1625-33. [PMID: 11049844 DOI: 10.1152/ajpregu.2000.279.5.r1625] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Activation of platelet-derived growth factor-beta (PDGF-beta) receptors in the nucleus of the solitary tract (nTS) modulates the late phase of the acute hypoxic ventilatory response (HVR) in the rat. We hypothesized that temporal changes in PDGF-beta receptor expression could underlie the ventilatory acclimatization to hypoxia (VAH). Normoxic ventilation was examined in adult Sprague-Dawley rats chronically exposed to 10% O(2), and at 0, 1, 2, 7, and 14 days, Northern and Western blots of the dorsocaudal brain stem were performed for assessment of PDGF-beta receptor expression. Although no significant changes in PDGF-beta receptor mRNA occurred over time, marked attenuation of PDGF-beta receptor protein became apparent after day 7 of hypoxic exposure. Such changes were significantly correlated with concomitant increases in normoxic ventilation, i.e., with VAH (r: -0.56, P < 0.005). In addition, long-term administration of PDGF-BB in the nTS via osmotic pumps loaded with either PDGF-BB (n = 8) or vehicle (Veh; n = 8) showed that although no significant changes in the magnitude of acute HVR occurred in Veh over time, the typical attenuation of HVR by PDGF-BB decreased over time. Furthermore, PDGF-BB microinjections did not attenuate HVR in acclimatized rats at 7 and 14 days of hypoxia (n = 10). We conclude that decreased expression of PDGF-beta receptors in the dorsocaudal brain stem correlates with the magnitude of VAH. We speculate that the decreased expression of PDGF-beta receptors is mediated via internalization and degradation of the receptor rather than by transcriptional regulation.
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Affiliation(s)
- O A Alea
- Department of Pediatrics, Tulane University School of Medicine, New Orleans, Louisiana 70112, USA
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Tansley JG, Fatemian M, Howard LS, Poulin MJ, Robbins PA. Changes in respiratory control during and after 48 h of isocapnic and poikilocapnic hypoxia in humans. J Appl Physiol (1985) 1998; 85:2125-34. [PMID: 9843535 DOI: 10.1152/jappl.1998.85.6.2125] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Ventilatory acclimatization to hypoxia is associated with an increase in ventilation under conditions of acute hyperoxia (VEhyperoxia) and an increase in acute hypoxic ventilatory response (AHVR). This study compares 48-h exposures to isocapnic hypoxia (protocol I) with 48-h exposures to poikilocapnic hypoxia (protocol P) in 10 subjects to assess the importance of hypocapnic alkalosis in generating the changes observed in ventilatory acclimatization to hypoxia. During both hypoxic exposures, end-tidal PO2 was maintained at 60 Torr, with end-tidal PCO2 held at the subject's prehypoxic level (protocol I) or uncontrolled (protocol P). VEhyperoxia and AHVR were assessed regularly throughout the exposures. VEhyperoxia (P < 0.001, ANOVA) and AHVR (P < 0.001) increased during the hypoxic exposures, with no significant differences between protocols I and P. The increase in VEhyperoxia was associated with an increase in slope of the ventilation-end-tidal PCO2 response (P < 0.001) with no significant change in intercept. These results suggest that changes in respiratory control early in ventilatory acclimatization to hypoxia result from the effects of hypoxia per se and not the alkalosis normally accompanying hypoxia.
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Affiliation(s)
- J G Tansley
- University Laboratory of Physiology, University of Oxford, Oxford OX1 3PT, United Kingdom
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Fatemian M, Robbins PA. Human ventilatory response to CO2 after 8 h of isocapnic or poikilocapnic hypoxia. J Appl Physiol (1985) 1998; 85:1922-8. [PMID: 9804600 DOI: 10.1152/jappl.1998.85.5.1922] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
During ventilatory acclimatization to hypoxia (VAH), the relationship between ventilation (VE) and end-tidal PCO2 (PETCO2) changes. This study was designed to determine 1) whether these changes can be seen early in VAH and 2) if these changes are present, whether the responses differ between isocapnic and poikilocapnic exposures. Ten healthy volunteers were studied by using three 8-h exposures: 1) isocapnic hypoxia (IH), end-tidal PO2 (PETO2) = 55 Torr and PETCO2 held at the subject's normal prehypoxic value; 2) poikilocapnic hypoxia (PH), PETO2 = 55 Torr; and 3) control (C), air breathing. The VE-PETCO2 relationship was determined in hyperoxia (PETO2 = 200 Torr) before and after the exposures. We found a significant increase in the slopes of VE-PETCO2 relationship after both hypoxic exposures compared with control (IH vs. C, P < 0.01; PH vs. C, P < 0.001; analysis of covariance with pairwise comparisons). This increase was not significantly different between protocols IH and PH. No significant changes in the intercept were detected. We conclude that 8 h of hypoxia, whether isocapnic or poikilocapnic, increases the sensitivity of the hyperoxic chemoreflex response to CO2.
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Affiliation(s)
- M Fatemian
- University Laboratory of Physiology, University of Oxford, Oxford OX1 3PT, United Kingdom
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Borel CO, Guy J, Barcik U, Natoli MJ, Vann RD. Effect of hypobaria on ventilatory and CO2 responses to short-term hypoxic exposure in cats. RESPIRATION PHYSIOLOGY 1998; 111:45-53. [PMID: 9496471 DOI: 10.1016/s0034-5687(97)00098-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The effect of hypobaria on the ventilatory response to short-term hypoxia was studied by comparing the respiratory mechanical and inspired CO2 ventilatory responses to hypobaric hypoxia (438 mmHg) with normobaric hypoxia (11.8% FIO2). Fifteen spontaneously breathing, anesthetized cats were divided into three groups of five: time control, normobaric hypoxia and hypobaric hypoxia. Measurements of ventilation, gas exchange, and responses to intermittent CO2 rebreathing were collected over a 4 h period. PaO2 fell to 44.5 +/- 2.7 mmHg, PaCO2 fell to 24.8 +/- 0.9, and pH rose to 7.49 +/- 0.01 in both hypoxic groups. Tidal volume did not change with respect to time or condition, but frequency and ventilation were significantly increased in the hypobaric hypoxic group. The slope of the CO2 response was unchanged over time or by condition. These results suggest that hypobaric hypoxia may alter the pattern of breathing responses to hypoxia but not the CO2-response. If metabolic rate remained constant, these results could be explained by a difference in dead space between hypoxic conditions.
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Affiliation(s)
- C O Borel
- Department of Anesthesiology, Duke University Medical Center, Durham, NC 27710, USA.
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A1077 EFFECT OF INSPIRED CO SUB 2 ON VENTILATORY RESPONSE TO HIGH ALTITUDE IN HUMANS. Anesthesiology 1997. [DOI: 10.1097/00000542-199709001-01077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Lahiri S. Peripheral Chemoreceptors and Their Sensory Neurons in Chronic States of Hypo‐ and Hyperoxygenation. Compr Physiol 1996. [DOI: 10.1002/cphy.cp040251] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Howard LS, Robbins PA. A comparison between the effects of 8 hours of isocapnic hypoxia and 8 hours of poikilocapnic hypoxia on respiratory control in humans. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1995; 393:277-81. [PMID: 8629496 DOI: 10.1007/978-1-4615-1933-1_52] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- L S Howard
- University Laboratory of Physiology, Oxford, United Kingdom
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17
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Bisgard GE. The role of arterial chemoreceptors in ventilatory acclimatization to hypoxia. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1994; 360:109-22. [PMID: 7872069 DOI: 10.1007/978-1-4615-2572-1_10] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- G E Bisgard
- Department of Comparative Biosciences University of Wisconsin Madison 53706
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18
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Abstract
We have reviewed evidence that hypoxic chemosensitivity is variable and that this variation may be both endowed, partly through genetic mechanisms, and acquired, and may reflect fundamental changes in carotid body function. This variation may influence the nature and effectiveness of adaptation to high altitude and to hypoxic disease states such as chronic obstructive pulmonary disease. High chemosensitivity seems to be the choice for coping with the casual exposure to hypoxia; but fundamental, highly effective adaptations, presumably at the level of peripheral tissue, seem to be the strategy of choice for professionally adapted species.
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Affiliation(s)
- J V Weil
- CVP Research Laboratory, Department of Medicine, University of Colorado Health Sciences Center, Denver
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Nicolaysen G, Ellingsen I, Owe JO, Myhre K. Arterial PCO2 and pH in man during 3 days' exposure to 2.8 kPa CO2 in the inspired gas. ACTA PHYSIOLOGICA SCANDINAVICA 1989; 135:399-403. [PMID: 2494844 DOI: 10.1111/j.1748-1716.1989.tb08593.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
It has not been firmly established how respiration adapts to long-term CO2 exposure in man. We have therefore exposed five healthy human subjects to 2.8 kPa CO2 in the inspired gas for about 70 h in a chamber with controlled atmospheric conditions at ambient pressure PCO2 and pH were determined in arterial or arterialized venous blood drawn before, during and after the exposure. One subject was studied twice. We found that PaCO2 increased acutely and then increased further within the 5- to 24-h period of exposure to 2.8 kPa CO2. No consistent change was observed during the following 2 days. At the end of exposure the PaCO2 was 0.5 kPa above the pre-exposure level. When the breathing gas was switched back to room air, PaCO2 promptly returned to pre-exposure values. The secondary rise in PaCO2 within the first day would correspond to a decrease in alveolar ventilation of about 10% assuming constant production and elimination of CO2. Arterial pH remained slightly below the pre-exposure level during the entire exposure period. A slight renal compensation resulting in an increase in base excess of about 1 mmol l-1 may have occurred in the middle part of the exposure period. We conclude that a significant, but moderate, respiratory adaptation takes place during the first day of exposure to an increased inspired load of CO2.
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Affiliation(s)
- G Nicolaysen
- Institute of Physiology, University of Oslo, Norway
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Moore LG, Cymerman A, Huang SY, McCullough RE, McCullough RG, Rock PB, Young A, Young P, Weil JV, Reeves JT. Propranolol blocks metabolic rate increase but not ventilatory acclimatization to 4300 m. RESPIRATION PHYSIOLOGY 1987; 70:195-204. [PMID: 3671899 DOI: 10.1016/0034-5687(87)90050-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Previously, we found resting metabolic rate increased at high altitude but the mechanism and consequences of this increase were unclear. We sought to test the role of beta-sympathetic activation for increasing metabolic rate and the contribution of an increase in metabolic rate to raising total ventilation at altitude. Following baseline studies at sea level, two groups of six healthy male subjects received either placebo or propranolol (80 mg/8 h) for 3 days prior to ascent to Pikes Peak (4300 m) where treatment was continued for 15 days. O2 consumption increased in placebo-treated subjects with a rise of 20 +/- 5% (X +/- SEM) on day 1 and no change 0 +/- 7% in propranolol-treated subjects (difference between groups, P less than 0.05). The increase in total ventilation upon ascent was 28 +/- 2% in the placebo group vs 9 +/- 7% in the propranolol group (P less than 0.05) and was correlated with metabolic rate in individual subjects. Decreasing end-tidal PCO2, taken as an index of ventilatory acclimatization, was similar in both groups. Thus, beta-sympathetic activation appears to increase metabolic rate upon ascent to high altitude and lead to a proportionate elevation in total ventilation but does not alter ventilatory acclimatization.
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Affiliation(s)
- L G Moore
- Cardiovascular Pulmonary Research Laboratory, University of Colorado Health Sciences Center, Denver 80262
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Moore LG, Cymerman A, Huang SY, McCullough RE, McCullough RG, Rock PB, Young A, Young P, Weil JV, Reeves JT. Propranolol blocks metabolic rate increase but not ventilatory acclimatization to 4300 m. ACTA ACUST UNITED AC 1987. [DOI: 10.1016/s0034-5687(87)80043-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Krasney JA, Hajduczok G, Miki K, Matalon S. Peripheral circulatory responses to 96 hours of eucapnic hypoxia in conscious sheep. RESPIRATION PHYSIOLOGY 1985; 59:197-211. [PMID: 3983486 DOI: 10.1016/0034-5687(85)90007-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Conscious sheep acclimatizing to hypoxia (PaO2 40 mm Hg, PaCO2 24 mm Hg) respond with increases in cardiac output (Qco) and cerebral blood flow lasting for 24 and 48 h, respectively. Coronary flow increases in a sustained fashion, while there are progressive decreases in renal, splenic and pancreatic flows. In the present study, 5 adult ewes were exposed to similar levels of normobaric hypoxia (PaO2 40 mm Hg) but the PaCO2 was maintained at eucapnic levels (32 mm Hg). VE increased (+210%) while VO2 decreased by 35%. Ventilatory sensitivity to CO2 was unchanged. Qco (thermodilution) was elevated for 96 h (+20%) as stroke volume was maintained at normoxic levels and heart rate increased (+36%). Pulmonary artery pressure increased (+35%) along with plasma catecholamine levels (+116-196%). There were sustained elevations of cerebral flow (radiolabelled microspheres) from 79.1 (+/- 9.2 SEM) to 121.6 ml X min-1 X 100 g-1 (+/- 10.8), coronary flow from 183 (+/- 22.1) to 373 ml X min-1 X 100 g-1 (+/- 46.3), diaphragm flow (+400%) and intercostal muscle flow (+186%) with no apparent redistribution of Qco. Therefore, the cardiac and peripheral circulatory response patterns are altered significantly in eucapnic hypoxia. The rate of O2 delivery to brain and several abdominal viscera is higher.
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Lahiri S, Edelman NH, Cherniack NS, Fishman AP. Role of carotid chemoreflex in respiratory acclimatization to hypoxemia in goat and sheep. RESPIRATION PHYSIOLOGY 1981; 46:367-82. [PMID: 7323494 DOI: 10.1016/0034-5687(81)90132-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The role of the carotid body chemoreflex in the ventilatory acclimatization to chronic hypoxia was studied in the unanesthetized goat and sheep. The time-cours of changes in ventilation, PCO2, pH and PO2 of arterial blood and cisternal fluid (CF) were measured before and following exposure to a simulated altitude of 3660-5000 m, with and without intact carotid sinus nerves. At sea level, after section of carotid sinus nerves most animals hypoventilated chronically, and developed mild arterial hypoxemia and hypercapnia. Upon exposure to acute hypoxia, all of the intact animals hyperventilated and CF pH increased from 7.310 to 7.380 whereas after chemodenervation, the increase in ventilation was small and delayed, and CF pH decreased from 7.285 to 7.143. During exposure of the intact animals to chronic hypoxia, hyperventilation accompanied by decreases in arterial and CF P CO2 reached its peak in two days; these changes partially subsided during the next few days. Partial compensation of respiratory alkalosis occurred during the first day. In contrast, several chemodenervated animals died during chronic hypoxia; the survivors showed either a small decrease or an increase in Pa CO2. Thus, an intact peripheral chemoreflex drive during hypoxia is necessary for ventilatory acclimatization which raises the arterial and presumably tissue PO2 in spite of alkalosis. The new proposal is that a central tissue metabolic acidosis resulting from a direct effect of acute hypoxia is partly compensated as hypoxia is prolonged. This central compensation decreases ventilatory drive and hence opposes the ventilatory acclimatization during chronic hypoxia initiated by the peripheral chemoreflexes.
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