Resting and exercising cardiorespiratory variables and acute mountain sickness

The incidence of Acute Mountain Sickness (AMS) is increasing. In a military context our current operational areas include mountainous regions with the implications of AMS including loss of operational tempo and logistical overstretch. Oxygen saturation and heart rate variability have in some studies been predictive of AMS while in others not. No single factor has been demonstrated consistently to be predictive of developing AMS.

During an expedition to climb Mt Aconcagua (6959m) we explored the relationship between cardiorespiratory variables and AMS. In 11 subjects we measured simple physiological variables and Lake Louise Score both pre and post a standardised exercise challenge at on arrival at different altitudes and after a period of acclimatization.

The changes in cardiorespiratory variables we observed with altitude were consistent with previous studies. Heart rate, respiratory rate and blood pressure increased whilst oxygen saturation reduced. Over time at altitude, respiratory rate and heart rate were maintained whilst there was a reduction in blood pressure towards sea level values. Oxygen saturations improved over time at altitude and the change in heart rate on exercise was reduced with acclimatization. In this small pilot study individuals with AMS may have a greater heart rate response to exercise than non-AMS subjects and this may warrant further investigation.

The incidence of AMS in our study was low reflecting a conservative ascent profile. Further larger studies are necessary to fully assess the predictive value of cardiorespiratory variables in AMS.