International Journal Of Sports Medicine

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

Despite extensive research in the field of acute mountain sickness, the pathophysiology and mechanisms that cause AMS are largely unknown. One common finding is a reduction of heart rate variability (HRV), thought to be secondary to a sympathetic predominance with suppression of vagal activity. This randomized crossover study examined the effect of hypoxia and exercise on the autonomic control of the heart and the prevalence of AMS. The authors of the study hypothesized that the additional stress of moderate exercise would cause a reduction of HRV and a corresponding exacerbation of AMS symptoms.

Twenty participants were placed in a normobaric hypoxic chamber (Fio₂ of 11%) to simulate the partial pressure of oxygen at 5500 m. Active exercise was defined as three 30-minute cycle ergometer sessions at 50% of each individual participant’s predetermined maximum. The primary outcomes were HRV and AMS symptoms defined by the Lake Louise Score. The investigators found a decrease in HRV in both passive and exercise groups, but with no statistical difference between the 2 groups. Further, HRV did not correlate with the incidence of AMS. Although exercise did not significantly increase the prevalence or severity of AMS, it did increase the prevalence of nongastrointestinal symptoms such as headache, fatigue, and dizziness (score 3.3 ± 1.7 vs 4.3 ± 1.6 exercise, P = .04).

The authors concluded that cardiac autonomic modulation during hypoxia does not influence the development of AMS. They speculated that the sympathetic predominance of moderate exercise may have a protective effect against nausea and vomiting while worsening nongastrointestinal symptoms of AMS.

(Int J Sports Med. 2013 Feb 5 [Epub ahead of print]) K Mairer, M Wille, W Grander, M Burtscher.