Physiological responses during ascent to high altitude and the incidence of acute mountain sickness.

Alexandra Cobb ,Edward Gilbert‐Kawai,Kay Mitchell,Daniel Hurlbut,Denny Levett ,P J Hennis ,Monty Mythen ,W Aveling ,Michael P.w Grocott ,Daniel Martin

doi:10.14814/phy2.14809

Abstract

Acute mountain sickness (AMS) occurs when there is failure of acclimatisation to high altitude. The aim of this study was to describe the relationship between physiological variables and the incidence of AMS during ascent to 5300 m. A total of 332 lowland‐dwelling volunteers followed an identical ascent profile on staggered treks. Self‐reported symptoms of AMS were recorded daily using the Lake Louise score (mild 3–4; moderate‐severe ≥5), alongside measurements of physiological variables (heart rate, respiratory rate (RR), peripheral oxygen saturation (SpO2) and blood pressure) before and after a standardised Xtreme Everest Step‐Test (XEST). The overall occurrence of AMS among participants was 73.5% (23.2% mild, 50.3% moderate–severe). There was no difference in gender, age, previous AMS, weight or body mass index between participants who developed AMS and those who did not. Participants who had not previously ascended >5000 m were more likely to get moderate‐to‐severe AMS. Participants who suffered moderate‐to‐severe AMS had a lower resting SpO2 at 3500 m (88.5 vs. 89.6%, p = 0.02), while participants who suffered mild or moderate‐to‐severe AMS had a lower end‐exercise SpO2 at 3500 m (82.2 vs. 83.8%, p = 0.027; 81.5 vs. 83.8%, p < 0.001 respectively). Participants who experienced mild AMS had lower end‐exercise RR at 3500 m (19.2 vs. 21.3, p = 0.017). In a multi‐variable regression model, only lower end‐exercise SpO2 (OR 0.870, p < 0.001) and no previous exposure to altitude >5000 m (OR 2.740, p‐value 0.003) predicted the development of moderate‐to‐severe AMS. The Xtreme Everest Step‐Test offers a simple, reproducible field test to help predict AMS, albeit with relatively limited predictive precision.

Highlights

We evaluated the performance of a simple exercise challenge at altitude in predicting acute mountain sickness (AMS) on a trek to Everest Base Camp (5300 m)
Prior to the COVID-19 pandemic, increasing numbers of people were travelling to high altitude, and it is likely that these numbers will return when domestic and international travel is freely available once again
We have demonstrated the potential value of a short step-exercise test conducted at moderate high altitude in predicting the development of AMS

Summary

Introduction

Prior to the COVID-19 pandemic, increasing numbers of people were travelling to high altitude, and it is likely that these numbers will return when domestic and international travel is freely available once again. Exposure to hypobaric hypoxia due to the reduction in partial pressure of oxygen occurs with increasing elevation. The Lake Louise scoring system was devised to aid in the diagnosis of AMS, provide a subjective scale for the description of symptoms and to facilitate research (Roach et al, 1993). The precise pathophysiology underlying AMS remains elusive, a number of hypotheses exist that may explain why the hypobaric hypoxia experienced at high altitude causes these symptoms (Wilson et al, 2009). SEVERAL risk factors for susceptibility to AMS have been previously identified, published data have been conflicting; these include a history of previous AMS, younger age, female gender, rapid ascent, obesity and increased exertion (Hackett & Roach, 2001; Honigman et al, 1993; MacInnis et al, 2013; Richalet et al, 2012)

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