Influence of Induced Altitude Acclimatization on Development of Acute Mountain Sickness Associated with a Subsequent Rapid Ascent to High Altitude

Abstract

Objective: Ascent to high altitudes requires adaptation to a hypoxic and hypobaric environment. Induced altitude acclimatization may decrease susceptibility to acute mountain sickness (AMS). We aimed to exam the effects of acclimatization at 1520m on susceptibility to AMS during a subsequent rapid ascent to 3658m. Methods: Rate pressure product (RPP), oxygen saturation (SpO2) and vascular tone, quantified by the reflection index (RI) obtained using photoplethysmography (PPG) technique, were studied in fifty-five participants ascending to 3658m from 300 and 1520m defined as Group A and B respectively. AMS occurrence was evaluated by the Lake Louise Score (LLS) system. Results: Seventeen of the fifty-five participants were diagnosed with AMS. The incidence and severity were lower in Group B than Group A. On initial exposure, we observed a significant increase of RPP and a significant decrease of SpO2. Inside each group, either A or B, RI exhibited a quick and dramatic fall followed by an early recovery back to normal in subjects without AMS but a blunted and slow fall followed by a delayed recovery in subjects with AMS. A moderate level of inverse correlation was found between degree of fall (Δ) in SpO2 and RI within 24 hours. Conclusions: The induced altitude acclimatization provided low-altitude residents in certain degree benefit in prevention of AMS during a subsequent rapid ascent to high altitude. The comparison of data between participants with and without an induced altitude acclimatization exhibited physiological significance during acute phase response after a rapid ascend to altitude.