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Increased hypoxic ventilatory response during 8 weeks at 3800 m altitude
Maarten D W Hupperets1, Susan R Hopkins, Marieke G Pronk
1Department of Medicine, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0623, USA.
Respiratory Physiology & Neurobiology
|September 29, 2004
Summary
Chronic hypoxia (CH) initially boosts ventilation, but prolonged exposure can cause desensitization. This study found no hypoxic desensitization in the first two months of CH, with ventilation remaining elevated.
Area of Science:
- Physiology
- Environmental Medicine
- Respiratory Physiology
Background:
- Acclimatization to chronic hypoxia (CH) typically increases ventilation and the hypoxic ventilatory response (HVR).
- However, prolonged exposure to CH (years) can lead to hypoxic desensitization, blunting the HVR.
- The occurrence of hypoxic desensitization within the initial months of CH remains unclear.
Purpose of the Study:
- To investigate whether hypoxic desensitization of the hypoxic ventilatory response (HVR) occurs during the first 8 weeks of chronic hypoxia (CH).
- To assess changes in hypoxic ventilatory decline (HVD) during this early acclimatization period.
Main Methods:
- Five healthy subjects were studied at sea level and during 8 weeks of exposure to 3800 m (CH).
- The isocapnic hypoxic ventilatory response (HVR) was measured using the change in ventilation relative to the change in oxygen saturation (Delta V(I)/Delta Sa(O(2))).
- Hypoxic ventilatory decline (HVD) was tested by reducing oxygen saturation to 80% after a period at 90%.
Main Results:
- The HVR significantly increased within 2 days of exposure to CH and remained elevated throughout the 8-week study period.
- No significant difference in hypoxic ventilatory decline (HVD) was observed between sea level conditions and 8 weeks of CH.
- The increased HVR during the initial 8 weeks of CH was not associated with changes in HVD.
Conclusions:
- Hypoxic desensitization of the HVR does not occur within the first 8 weeks of chronic hypoxia.
- The observed increase in HVR during early acclimatization to CH is independent of changes in hypoxic ventilatory decline.