Respiratory acclimatization and psychomotor performance after rapid ascent and during 3 weeks at 3100 m. A prospective cohort study in healthy.

BackgroundThe acclimatization to high altitudes over several weeks is not extensively studied. Repeated physiological assessments were performed in healthy lowlanders staying at 3100m for 3 weeks. We hypothesized that over the course of 3 weeks, the arterial oxygen saturation (SpO2) improves and has favorable effects on psychomotor vigilance, postural control, and sleep. Methods16 healthy volunteers (23-33y) underwent sleep studies during 1 night in Bishkek (760m), and during nights 1, 8 and 22 at Too-Ashu (3100m), Kyrgyzstan. The day after, reaction time (psychomotor vigilance test reaction time test, PVT) and postural control (center of gravity path length on balance board [COPL]) were assessed. ResultsCompared to 760m, mean nocturnal SpO2 dropped in the first night at 3100m from mean{+/-}SD 94.8{+/-}1.9% to 86.3{+/-}2.9% and recovered partially to 89.8{+/-}1.5% after 3 weeks (P<0.05 both comparisons to 760m). Corresponding median (quartiles) oxygen desaturation indices were 1.0/h(0.3;2.2), 6.5/h(4.5;12.1) and 6.4/h(4.2;11.1) time in bed (P<0.05 both comparisons to 760m). Median (quartiles) reaction times were 226ms(212;231), 236ms(210;259) and 228ms(212;246), P=NS, all comparisons. COPL worsened from 25.1{+/-}4.1cm to 27.1{+/-}4.1cm (P<0.05) and 26.4{+/-}3.7cm (P=NS compared to 760m). ConclusionIn healthy lowlanders staying at 3100m, nocturnal SpO2 increased over 3 weeks after an initial drop but did not reach 760m baseline values. Postural control was impaired in the first week of acute exposure to high altitude despite improvements in hypoxemia. Altitude exposure had no effect on reaction time. Thus, acute and prolonged exposure to hypobaric hypoxia has differential effects on oxygenation, control of breathing, postural control and reaction time.