Predictive Models of Acute Mountain Sickness after Rapid Ascent to Various Altitudes

Abstract

Despite decades of research, no predictive models of acute mountain sickness (AMS) exist, which identify the time course of AMS severity and prevalence following rapid ascent to various altitudes. Using general linear and logistic mixed models and a comprehensive database, we analyzed 1292 AMS cerebral factor scores in 308 unacclimatized men and women who spent between 4 and 48 h at altitudes ranging from 1659 to 4501 m under experimentally controlled conditions (low and high activity). Covariates included in the analysis were altitude, time at altitude, activity level, age, body mass index, race, sex, and smoking status. AMS severity increased (P < 0.05) nearly twofold (i.e., 179%) for every 1000-m increase in altitude at 20 h of exposure, peaked between 18 and 22 h of exposure, and returned to initial levels by 48 h of exposure regardless of sex or activity level. Peak AMS severity scores were 38% higher (P < 0.05) in men compared with women at 20 h of exposure. High active men and women (>50% of maximal oxygen uptake for >45 min at altitude) demonstrated a 72% increase (P < 0.05) in the odds (odds ratio, 1.72; confidence interval, 1.03-3.08) of AMS compared with low active men and women. There was also a tendency (P = 0.10) for men to demonstrate greater odds of AMS (odds ratio, 1.65; confidence interval, 0.84-3.25) compared with women. Age, body mass index, race, and smoking status were not significantly associated with AMS. These models provide the first quantitative estimates of AMS risk over a wide range of altitudes and time points and suggest that in addition to altitude and time at altitude, high activity increases the risk of developing AMS. In addition, men demonstrated increased severity but not prevalence of AMS.