Control of ventilation in climbers to extreme altitude.

Blunted chemosensitivity has been found in successful endurance athletes and some high-altitude natives. This characteristic, however, may not be beneficial to climbers at extreme altitude, where a vigorous ventilatory response to hypoxia may be of value in enhancing alveolar and arterial oxygenation. We studied 14 climbers who had climbed to 7,470 m or higher, 10 age-matched controls, and 10 outstanding middle- and long-distance runners. The ventilatory response to progressive hypoxia was determined at a constant, normal end-tidal Pco2 over 8-12 min and to CO2 by rebreathing a 7% CO2 hyperoxic mixture (Read technique). The hypoxic response parameter of Weil, A was used to determine the hypoxic responses and S (delta VE/ delta PACO2) the hypercapnic response. Climbers had A values significantly higher than the runners (means +/- SE: 158.9 +/- 29.9 vs. 49.3 +/- 7.1, P less than 0.001) but not significantly higher than the controls (109.9 +/- 21.0). delta VE/ delta PACO2 of climbers was higher (3.0 +/- 0.4) than both controls (2.2 +/- 0.2, P less than 0.025) and runners (1.4 +/- 0.2, P less than 0.0005). These data suggest that successful climbers to extreme altitude may be selected by virtue of their vigorous respiratory responses to hypoxia to maintain adequate oxygenation in the presence of extreme environmental hypoxia.