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

Lara Muralt ¹ Mona Lichtblau ^1,2 Sayaka S Aeschbacher ¹ Maya Bisang ¹ Kay Von Grünigen ¹ Talant M Sooronbaev ^2,3 Silvia Ulrich ^1,2 Konrad E. Bloch ^1,2 Michael Furian ^1,2,4*

• ¹ Pulmonary Division and Sleep Disorders Center, University Hospital Zürich, Zurich, Zürich, Switzerland
• ² Kyrgyz-Swiss High Altitude Medical Research Center, Tuja-Ashu, Kyrgyzstan
• ³ National Center of Cardiology and Internal Medicine (Kyrgyzstan), Bishkek, Kyrgyzstan
• ⁴ Research Department, Swiss TCM University, Bad Zurzach, Switzerland

Acclimatization to high altitudes over several weeks has not been extensively studied.Repeated physiological assessments were performed in healthy lowlanders staying at 3100m for 3 weeks. We hypothesized that acute exposure to 3100m results in hypoxemia, sleepdisordered breathing, and postural instability, while a 3-week pre-acclimatization at 3100m will improve these outcomes. Methods 16 healthy volunteers (23-33y) underwent nocturnal pulse oximetry and nasal airflow monitoring during 1 night in Bishkek (760m), and during nights 1, 8 and 22 at Too-Ashu (3100m), Kyrgyzstan. On each day after monitoring, reaction time (psychomotor vigilance test reaction time test, PVT) and postural control (center of gravity path length on balance board [COPL]) were assessed.Compared 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).In healthy lowlanders staying at 3100m, nocturnal SpO2 increased over 3 weeks after an initial drop but did not reach baseline values. Postural control was impaired in the first week of acute exposure to high altitude despite improvements in hypoxemia. Altitude exposure did not affect reaction time. Thus, acute and prolonged exposure to hypobaric hypoxia has differential effects on oxygenation, control of breathing, postural control, and reaction time.