Oxygen saturation and acute mountain sickness during repeated altitude exposures simulating high-altitude working schedules
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Objective
To quantify the effect of two consecutive prolonged, intermittent exposures to high and very high altitudes on oxygen saturation (SpO 2 ) and acute mountain sickness (AMS).
Methods
Healthy lowlanders (N=21), aged 18-30y, underwent two 7-day sojourns at the ALMA observatory, Chile (6hrs/day at 5050m, 18hrs/day at 2900m), separated by 1-week at 520m. SpO 2 (pulse oximetry) and AMS severity (AMSc, Environmental Symptom Questionnaire cerebral score) diagnosing AMS (AMSc≥0.7) were assessed daily at both altitudes. www.ClinicalTrials.gov:NCT02730143 .
Results
SpO 2 at 2900m and 5050m on arrival day was mean±SD 93.6±0.5% and 79.9±1.0% (P<0.05 between altitudes), whereas the AMSc scores were 0.43±0.08 and 0.97±0.11 (P<0.05 between altitudes), respectively. At 2900m during a 7-day intermittent hypoxic exposure, SpO 2 increased by a mean(95%CI) 0.3%/day(0.1;0.4) and by 0.9%/day(0.4;1.3) at 5050m. Similarly, AMSc decreased by 0.05points/day(0.01;0.08) at 2900m and by 0.16points/day(0.11;0.21) at 5050m. During the second sojourn (vs. 1 sojourn), day1, SpO 2 at 2900m was unchanged but higher at 5050m by 2.9%(0.6;5.3). AMSc was lower at 2900m and 5050m by 0.37(0.16;0.59) and 0.37(0.11;0.63) (P<0.05 both comparisons vs 1 sojourn), respectively. Acclimatization with the 2 sojourn resulted in an increase in SpO 2 at 2900m by 0.3%/day(0.1;0.4) and at 5050m: 0.5%/day(0.1;0.8). AMSc remained unchanged with acclimatization at 2900m but decreased at 5050m by 0.08points/day(0.04;0.11).
Conclusions
In healthy lowlanders, a 7-day intermittent hypobaric hypoxic exposure of varying severity at high and very high altitude improved SpO 2 and AMS severity at 2900m, with larger improvements at 5050m. During a second identical sojourn, initial AMS severity was reduced despite comparable SpO 2 at 2900m compared to the 1 sojourn. No further acclimatization effects were observed in SpO 2 but in AMS symptoms at 2900m. In contrast, re-exposure to 5050m showed higher initial SpO 2 and lower AMSc values with further improvement with intermittent re-exposures. These findings highlight altitude-dependent acclimatization patterns and confirm the effectiveness of pre-conditioning to prevent AMS when planning sojourns to high altitudes.
