Hypoxic ventilatory response during rest and exercise after a Himalayan expedition

Abstract

Hypoxic ventilatory response (HVR) was examined before and after acclimatization to high altitude. Transient hyperoxic switches according to Dejours's technique were used to examine the contribution of HVR to the hyperpnoea of increasing exercise intensities. Ten mountaineers were exposed to hypoxia (oxygen fraction in inspired gas. F1O2 = 0.11, 79 mmHg) before the expedition and after return from altitude (56 days, 30 days at 4900 m or higher). After 25-min breathing hypoxic gas, the subjects performed a maximal cycle ergometer test (increments 50 W per 5 min). Respired gases and ventilation (VE) were analysed breath-by-breath, partial pressure of oxygen (PO2) and oxygen saturation (SO2) were measured in capillary blood. The HVR was tested by switching two breaths to an F1O2 of 1.0. The nadir of VE after the switch was measured (decrease in ventilation, DVE). The HVR was expressed as the DVE at a PO2 of 40 mmHg (DVE40) and the DVE versus decrease of SO2 (DVE/[100-SO2]). The HVR estimated by DVE40 increased from 19.9 to 28.0 l.min-1 (median, P = 0.013). The HVR expressed as DVE (100-SO2) at rest was no different before and after acclimatization (0.89 and 0.86 l.min-1.%-1 respectively) and during exercise it did not change before the expedition (0.83 l.min-1. %-1). However, DVE/(100-SO2) increased significantly with exercise intensity after the expedition (1.61 l.min-1.% at 200 W). The changes of DVE versus SO2 as well as of DVE versus VE were steeper after the expedition than before. In summary, after return from 30 day at high altitude, an increased HVR was observed. The augmentation of HVR was evident at higher exercise intensities and we suggest that this reflects a change in sensitivity of the peripheral chemoreflex loop.