Ventilatory responses to hypercapnia and hypoxia before and after high altitude mountaineering

The present study was designed to ascertain whether or not ventilatory response to hypercapnia at rest and to hypoxia during submaximal exercise at sea level increased after high altitude mountaineering. Two groups of subjects were studied: one (Andes) group consisted of 10 men and 4 women who had participated in the ascent of Mt. Huascaran (6,768 m) and the other (Himalaya) consisted of 10 men and 3 wemen who had participated in the ascent of Mt. Tent peak (5,760 m). Ventilatory response to CO2 was determined by Read's rebreathing technique. In order to measure hypoxic ventilatory, drive during exercise, the subject performed exercise on a bicycle ergometer for 8 min with a work load of 1.5 kp for males and 1.0 kp for females at a constant rate of 60 rpm. Minute ventilation breathing of room air (VE(nor)) and low (about 10%) oxygen (VE(hypo)) was measured: in this experiment, the ratio of VE(hypo) to VE(nor)(VE(hypo)/VE(nor)) was used as an index of hypoxic ventilatory response during submaximal exercise. It was found in this study that average VE(nor), VE(hypo) and VE(hypo)/VE(nor) values increased significantly (p<0.05-0.01) after mountaineering in both groups except VE(nor) in the Andes group, while the slope of ventilatory respons to hypercapnia at rest was almost the same before and after high altitude mountaineering. These results suggest that elevated ventilatory response to hypoxia during submaximal exercise was still maintained for at least 1 or 2 weeks after returning to sea level, but not hypercapnia at rest.