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Hypoxic ventilatory response during rest and exercise after a Himalayan expedition
J M Steinacker1, A Halder, Y Liu
1Abt. Sport- und Leistungsmedizin, Universität Ulm, Germany.
Summary
High altitude acclimatization enhances the hypoxic ventilatory response (HVR), particularly during exercise. This suggests increased sensitivity in the peripheral chemoreflex loop after returning from high altitudes.
Area of Science:
- Physiology
- Altitude Medicine
- Respiratory Control
Background:
- The hypoxic ventilatory response (HVR) is crucial for maintaining oxygen levels during hypoxia.
- Acclimatization to high altitude is known to alter physiological responses, but its specific impact on HVR during exercise requires further elucidation.
Purpose of the Study:
- To investigate the changes in HVR before and after acclimatization to high altitude.
- To determine the contribution of HVR to ventilation during increasing exercise intensities post-altitude exposure.
Main Methods:
- Ten mountaineers underwent hypoxic exposure (FiO2 = 0.11) and maximal cycle ergometer tests before and after 30 days at high altitude (≥4900 m).
- The Dejours's technique (transient hyperoxic switches) was employed to measure the decrease in ventilation (DVE) as an indicator of HVR.
- HVR was quantified as DVE at a PO2 of 40 mmHg (DVE40) and DVE per decrease in oxygen saturation (DVE/[100-SO2]).
Main Results:
- HVR, estimated by DVE40, significantly increased after acclimatization (19.9 to 28.0 l.min-1).
- While resting HVR did not change, the HVR relative to oxygen saturation decrease (DVE/[100-SO2]) significantly increased with exercise intensity after acclimatization (1.61 l.min-1.% at 200 W).
- The relationship between DVE and oxygen saturation/ventilation became steeper post-acclimatization.
Conclusions:
- High altitude acclimatization leads to an augmented hypoxic ventilatory response.
- This augmentation is more pronounced at higher exercise intensities, suggesting altered peripheral chemoreflex sensitivity.