Hypoxic ventilatory response and acute mountain sickness.

The acute ventilatory response to hypoxia (HVR) and to hypercapnia (CO2VR) was measured in 32 members of two mountaineering expeditions prior to their departure. Both teams made rapid ascents to their base camps at 5200 m and 4300 m and remained there for at least four days. Symptom scores for acute mountain sickness (AMS) were collected daily for these four days. There was a range of AMS from the unaffected to severe sickness requiring evacuation, but there was no correlation between AMS scores and HVR or CO2VR. When ascent to altitude takes a day or more, HVR (measured at sea level) is probably not the major determinant of ventilation and from our studies does not predict susceptibility to AMS. The rate of respiratory acclimatization is probably more important.