The influence of high-altitude acclimatization on ventilatory and blood oxygen saturation responses during normoxic and hypoxic testing

Abstract

We investigated how acclimatization effects achieved during a high-altitude alpinist expedition influence endurance performance, ventilation (VE${\dot V-E}$) and blood oxygen saturation (SaO2) in normoxic (NOR) and hypoxic conditions (HYP). An incremental testing protocol on a cycle ergometer was used to determine the power output corresponding to the Lactate (PLT) and Ventilatory Threshold (PVT) in NOR and HYP (FiO2=0.13) as indirect characteristics of endurance performance in both conditions. Furthermore, changes in VE${\dot V-E}$, SaO2, blood pH and Pco2 were measured at a similar absolute exercise intensity of 180 W in NOR and HYP conditions. Seven experienced alpinists (mean ± SD: age: 50 ± 6 yrs; body mass: 76 ± 5 kg; body height: 175 ± 8 cm) volunteered to participate in this study after they had reached the summit of Gasherbrum II and Ama Dablam. They had therefore experienced the limitations of their acclimatization. Individual differences of PLT between values reached after and before the expedition (PLT) correlated (r = 0.98, p = 0.01) with differences of SaO2 (SaO2) in HYP, and differences of PVT (PVT) correlated (r = -0.83, p = 0.02) with differences of VE(ΔVE)${\dot V-E}\left( {\Delta {{\dot V}-E}} \right)$ in HYP. The results suggest that the acclimatization may not have an equivocal and simple influence on the performance in hypoxia: enhanced blood oxygen saturation may be accompanied by increased endurance only, when the increase exceeded 2-3%, but enhanced ventilation, when increased more than 10 l/min in HYP, could detrimentally influence endurance.