Abstract
Background
Previous studies have addressed the changes of peripheral or cerebral oxygenation that occur with ascent to altitude and acclimatization. None of these studies have explicitly examined the relationship between peripheral and cerebral oxygenation.
Methods
11 subjects from the Xtreme Alps medical research expedition were studied at sea level and 2 and 7 days after ascent to 4559 m. Near-infrared spectroscopy and pulse oximetry were used to measure cerebral and peripheral oxygenation, respectively, while capnography was used to measure end-tidal CO2.
Results
Peripheral oxygenation decreased from 98% ± 1.4% at sea level to 80.2% ± 4.7% at day 2 at altitude before rising to 85.1% ± 4.7% after 7 days. While peripheral oxygenation dropped initially before rebounding at altitude, cerebral oxygenation continued to decline, decreasing from 68.8% ± 4.0% at sea level to 65.0% ± 6.2% after 2 days at altitude and further to 62.3% ± 4.7% at day 7. End-tidal CO2 decreased from 4.5 ± 0.8 kPa at sea level to 3.4 ± 0.4 kPa after 2 days at altitude and to 3.1 ± 0.5 kPa after 7 days at altitude. Both resting SpO2 (ρ = .441, P = .019) and ETCO2 (ρ = 0.491, P <.01) were correlated with cerebral oxygenation.
Conclusions
Improvement in peripheral oxygenation is not a reliable predictor of increasing cerebral oxygenation at altitude, as this divergence in SpO2 and SctO2 between days 2 and 7 at altitude illustrates. This divergence may be attributable to the differences in the response to CO2 between the periphery and the central nervous system. At simulated extreme altitudes there is a significant correlation between subjects with a more pronounced hypoxic ventilatory response (HVR) and increased impairment on a variety of cognitive tasks. This contrasts with other reports demonstrating improved climbing performance in subjects with a higher HVR. This dichotomy between athletic and cognitive performance parallels the divergence between peripheral and cerebral oxygenation seen in the present study.