Residence at moderate versus low altitude is effective at maintaining higher oxygen saturation during exercise and reducing acute mountain sickness following fast ascent to 4559 m

Objective: to continuously monitor oxygen saturation by pulse oximeter (SpO2) and assess the development of acute mountain sickness (AMS) using the Lake Louise Score (LLS) during ascent from 1154 m to 4559 m in 2 groups of subjects. Ten moderate altitude residents (≥1000-≤2500 m, MAR) and 34 low altitude residents (LAR). MAR are reported to have a lower incidence of AMS during ascent to higher altitudes compared with LAR. Whether this is related to higher SpO2 is still open to debate. Methods: Seventy subjects were recruited; 24-hour SpO2 monitoring with finger pulse oximetry was performed. All subjects rode a cable car from 1154 m to 3275 m and then climbed to 3647 m where 60 subjects (LAR) overnighted. The second day, 34/60 LAR reached the highest altitude. Ten subjects permanently living between 1100-1400 m (MAR) climbed directly to 4559 m without an overnight stop. Results: One LAR was excluded from the analysis as he performed a pre-acclimatization. We compared data of 10 MAR with data of 33 LAR who reached 4559 m. Two MAR had LLS =3 and 8 scored <3. Six LAR had an LLS of 3-4, 8 scored ≥5 and 19 scored <3. SpO2 monitoring showed higher mean SpO2 in MAR during ascent above 3600 m compared to LAR (MAR 79.1±4% vs LAR 75.5±5%; ANOVA, P=0.03). Conclusions: The results of this preliminary study suggest that residence at moderate altitude allows maintenance of higher SpO2 and reduced risk of developing AMS during rapid ascent to higher altitude.