Acute mountain sickness, chemosensitivity, and cardiorespiratory responses in humans exposed to hypobaric and normobaric hypoxia

Author:

Richard Normand A.1,Sahota Inderjeet S.2,Widmer Nadia3,Ferguson Sherri42,Sheel A. William1,Koehle Michael S.125

Affiliation:

1. School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada;

2. Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada; and

3. Department of Medicine, University of British Columbia, Vancouver, British Columbia, Canada;

4. Environmental Medicine and Physiology Unit, Faculty of Science, Simon Fraser University, Burnaby, British Columbia, Canada;

5. Division of Sport Medicine, Department of Family Practice, Vancouver, British Columbia, Canada

Abstract

We examined the control of breathing, cardiorespiratory effects, and the incidence of acute mountain sickness (AMS) in humans exposed to hypobaric hypoxia (HH) and normobaric hypoxia (NH), and under two control conditions [hypobaric normoxia (HN) and normobaric normoxia (NN)]. Exposures were 6 h in duration, and separated by 2 wk between hypoxic exposures and 1 wk between normoxic exposures. Before and after exposures, subjects ( n = 11) underwent hyperoxic and hypoxic Duffin CO2 rebreathing tests and a hypoxic ventilatory response test (HVR). Inside the environmental chamber, minute ventilation (V̇e), tidal volume (Vt), frequency of breathing ( fB), blood oxygenation, heart rate, and blood pressure were measured at 5 and 30 min and hourly until exit. Symptoms of AMS were evaluated using the Lake Louise score (LLS). Both the hyperoxic and hypoxic CO2 thresholds were lower after HH and NH, whereas CO2 sensitivity was increased after HH and NH in the hypoxic test and after NH in the hyperoxic test. Values for HVR were similar across the four exposures. No major differences were observed for V̇e or any other cardiorespiratory variables between NH and HH. The LLS was greater in AMS-susceptible than in AMS-resistant subjects; however, LLS was alike between HH and NH. In AMS-susceptible subjects, fB correlated positively and Vt negatively with the LLS. We conclude that 6 h of hypoxic exposure is sufficient to lower the peripheral and central CO2 threshold but does not induce differences in cardiorespiratory variables or AMS incidence between HH and NH.

Publisher

American Physiological Society

Subject

Physiology (medical),Physiology

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