Effects of Exercise and Hypoxia on Heart Rate Variability and Acute Mountain Sickness

Abstract

Acute mountain sickness (AMS) is a common condition among non-acclimatized individuals ascending to high altitude. Exercise, a characteristic feature of hiking and mountaineering, has been suggested to exacerbate AMS prevalence and to cause modifications of the autonomic nervous system. A reduction of the heart rate variability (HRV) is a common finding during acute hypoxia, however characteristics of HRV during exercise in subjects suffering from AMS are unknown. Therefore, the aim of the present study was to investigate the effects of acute normobaric hypoxia (FiO2=11.0% ≙ 5 500 m) at rest (PHE) and during exercise (AHE) on the cardiac autonomic function and the development of AMS in 20 healthy, male individuals. HRV recordings were performed during normoxia and after 2, 4, 6 and 8 h in hypoxia during PHE and AHE, respectively. AMS was assessed using the Lake Louise Score. During PHE 50% of participants developed AMS and 70% during AHE (p=0.22). The analysis of HRV data showed a significant reduction of total power (TP), high frequency (HF) and low frequency (LF) components and an increase of the LF:HF ratio during PHE, however without further modification during AHE. Exercise did not increase AMS prevalence or severity, but increased "non-gastrointestinal" symptoms including headache, fatigue and dizziness. HRV indices were not related to the overall incidence of AMS or the development of "non-gastrointestinal" symptoms but we detected significant correlations between gastrointestinal complaints and HRV components. Thus, we suggest that the cardiac autonomic modulation during acute normobaric hypoxia does not play an important role in the development of AMS, but seems to be related to gastrointestinal complaints at high altitude. However, the influence of moderate exercise on HRV and AMS is minor, only "non-GI" symptoms seem to be exacerbated when exercise is applied.

Sightings edited by Erik R. Swenson and Peter Bärtsch

“…A minor exacerbation of AMS by exercise cannot be excluded because of the low statistical power and a small trend to higher AMS scores and prevalence with exercise. This study confirms the results of recent publications which showed no effect of moderate exercise on AMS in normobaric hypoxia (Mairer et al, 2013;Schommer et al, 2012).…”

High Altitude Affects Nocturnal Non-linear Heart Rate Variability: PATCH-HA Study

“…However, the majority of the published data relate to short-term HRV recordings (1–5 min) obtained conducted in hypoxic chambers during ‘simulated’ rather than genuine terrestrial HA (Vigo et al, 2010; Prabhakaran and Tripathi, 2011; Mairer et al, 2013; Zhang et al, 2014). The hypoxic period examined has been generally brief (minutes to <8 h) with a tendency to assess at a single HA (Saito et al, 2005; Sutherland et al, 2017) leading to an under appreciation of the influence of acclimatization on HRV.…”

Predicting sickness during a 2-week soccer camp at 3600 m (ISA3600)

“…There is conflicting data on the responses of the autonomic nervous system to sickness at high altitude, with studies reporting either unaffected18 or increased9 11 markers of (cardiac) sympathetic activity. Exercise heart rate was largely increased before sickness, suggestive of an increased sympathetic activity during exercise 11.…”