The Influence of High-Altitude Acclimatization on Ventilatory and Blood Oxygen Saturation Responses During Normoxic and Hypoxic Testing

We investigated how acclimatization effects achieved during a high-altitude alpinist expedition influence endurance performance, ventilation ((V) over dot(E)) and blood oxygen saturation (SaO(2)) 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 (P-LT) and Ventilatory Threshold (P-VT) in NOR and HYP (FiO(2)=0.13) as indirect characteristics of endurance performance in both conditions. Furthermore, changes in (V) over dot(E), SaO(2), blood pH and Pco(2) 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 P-LT between values reached after and before the expedition (Delta P-LT) correlated (r = 0.98, p = 0.01) with differences of SaO(2) (Delta SaO(2)) in HYP, and differences of P-VT (Delta P-VT) correlated (r = -0.83, p = 0.02) with differences of (V) over dot(E) (Delta(V) over dot(E)) 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.