Autonomic responses of high-altitude natives during sojourn at plains and on return to altitude.

The study was conducted on 20 high-altitude natives (HAN-I) 19-32 years old, to evaluate the changes in autonomic responses during their 2-months sojourn on the plains, and on return to high altitude (HA). The autonomic indices measured were heart rate HR), blood pressure (BP), oral temperature (Tor), mean skin temperature (Tsk), respiratory rate (RR), Cold pressor response (CPR), HR-response to tilt at 70 degree, and alpha index (AI) of EEG (occipital). These indices were recorded periodically during the 2 months of their stay on the plains, and thereafter on return to altitude for a period of 1 month. For comparison, the same responses were studied on 10 lowlanders (LL) on the plains and on induction to HA along with HAN-I. The study was repeated at altitude, once on 10 HAN who had never been to the plains (HAN-II) and on 10 acclimatised lowlanders. The results suggest that the relative parasympathetic dominance observed in natives at HA showed a gradual decrease during their sojourn on the plains, probably due to the elevation in sympathetic activity. On return to high altitude, they showed further increase in sympathetic excitation, as observed in LL on acute induction, but the magnitude of this response was less in natives. However, they showed a trend to faster return of autonomic responses to their initial level compared to LL.