Active ascent accelerates the time course but not the overall incidence and severity of acute mountain sickness at 3,600 m

Abstract

Acute mountain sickness (AMS) typically peaks following the first night at high altitude (HA) and resolves over the next 2-3 days, but the impact of active ascent on AMS is debated. To determine the impact of ascent conditions on AMS, 78 healthy Soldiers (mean±SD; age=26±5yr) were tested at baseline residence, transported to Taos, NM (2845m), hiked (n=39) or were driven (n=39) to HA (3600m), and stayed for 4 days. AMS-Cerebral Factor Score (AMS-C) was assessed at HA twice on day 1 (HA1), five times on days 2 and 3 (HA2 and HA3) and once on day 4 (HA4). If AMS-C was ≥0.7 at any assessment, individuals were AMS susceptible (AMS+;n=33); others were non-susceptible (AMS─;n=45). Daily peak AMS-C scores were analyzed. Ascent conditions (active vs. passive) did not impact the overall incidence and severity of AMS at HA1-HA4. The AMS+ group, however, demonstrated a higher (p<0.05) AMS incidence in the active versus passive ascent cohort on HA1 (93 vs. 56%), similar incidence on HA2 (60 vs. 78%), lower incidence (p<0.05) on HA3 (33 vs. 67%), and similar incidence on HA4 (13 vs. 28%). The AMS+ group also demonstrated a higher (p<0.05) AMS severity in the active versus passive ascent cohort on HA1 (1.35±0.97 vs. 0.90±0.70), similar score on HA2 (1.00±0.97 vs. 1.34±0.70), and lower (p<0.05) score on HA3 (0.56±0.55 vs. 1.02±0.75) and HA4 (0.32±0.41 vs. 0.60±0.72). Active compared to passive ascent accelerated the time course of AMS with more individuals sick on HA1 and less individuals sick on HA3 and HA4.