Relationship of hypoxic ventilatory response to exercise performance on Mount Everest

At very high altitude, exercise performance in the human sojourner may depend on a sufficient hypoxic ventilatory response (HVR). To study the relationship of HVR to exercise performance at high altitude, we studied HVR at sea level and 5,400 m and exercise ventilation at sea level, 5,400 m, and 6,300 m in 9 members of the American Medical Research Expedition to Everest. The relationship of HVR between individuals was maintained when HVR was repeated after acclimatization to 5,400 m (P < 0.05). There was a significant correlation in all subjects between HVR and ventilatory equivalent during exercise at sea level (r = 0.704, P < 0.05). Subjects were then grouped into high (H) and low (L) HVR responders (ventilation increase to end-tidal PO₂ of 40 Torr = 21.2 ± 5.4 and 5.6 ± 0.9 l.min^-1, respectively. At low and moderate levels of exercise, ventilation at sea level and after acclimatization to 6,300 m was higher in the high HVR group. At 6,300 m blood O₂ saturation (Sa(O₂)%) decreased from rest to maximum exercise: H = 8.3 ± 1.8%, L = 20.0 ± 2.5% (P < 0.01). HVR correlated inversely in all subjects with the decrease in Sa(O₂) from rest to maximum exercise (P < 0.05). Climbers with the highest HVR values reached and slept at higher altitudes. We conclude that 1) the relative value of HVR in our group of climbers was not significantly altered after acclimatization; 2) HVR predicts exercise ventilation at sea level and high altitude; 3) the drop in Sa(O₂)% that occurs with exercise is inversely related to HVR; and 4) sojourners with high HVR may perform better at extreme altitude.