Voluntary Increase of Minute Ventilation for Prevention of Acute Mountain Sickness.

This study evaluated the feasibility and efficacy of voluntary sustained hyperventilation during rapid ascent to high altitude for the prevention of acute mountain sickness (AMS). Study subjects (n=32) were volunteer participants in a 2-day expedition to Mount Leoneras (4954 m), starting at 2800m (base camp at 4120 m). Subjects were randomized to either: 1) an intervention group using the voluntary hyperventilation (VH) technique targeting an end-tidal CO2 (ETCO2)<20 mmHg; or 2) a group using acetazolamide (AZ). During the expedition, respiratory rate (28±20 vs. 18±5 breaths/min, mean±SD, P<0.01) and SpO2 (95%±4% vs. 89%±5%, mean±SD, P<0.01) were higher, and ETCO2 (17±4 vs. 26±4 mmHg, mean±SD, P<0.01) was lower in the VH group compared to the AZ group - as repeatedly measured at equal fixed intervals during the ascent - showing the feasibility of the VH technique. Regarding efficacy, the incidence of 6 (40%) subjects registering an LLS score≥3 in the VH group was non-inferior to the 3 (18%) subjects in the acetazolamide group (P=0.16, power 28%). Voluntary increase in minute ventilation is a feasible technique, but - despite the underpowered non-inferiority in this small-scale proof-of-concept trial - it is not likely to be as effective as acetazolamide to prevent AMS.