THE EFFECT OF ALTITUDE PRE-ACCLIMATIZATION ON ACUTE MOUNTAIN-SICKNESSDURING REEXPOSURE

Background: Acclimatization to high altitude appears to prevent acute mountain sickness (AMS), as evidenced by a decline in AMS symptoms as acclimatization progresses. Hypothesis: We hypothesized that partial r etention of acclimatization would attenuate the incidence and/or sever ity of AMS upon reinduction to altitude. Methods: To test this hypothe sis 6 male lowlanders returned to sea level after acclimatizing for 16 d at 4300 m (HA). After 8 d at sea level (PA), they were reexposed to 4300 m in a hypobaric chamber for 30 h (RA). AMS symptom severity was determined by the AMS-cerebral (AMS-C) scores calculated from the dai ly administration of the Environmental Symptoms Questionnaire during H A and RA. Results: The mean AMS-C scores were reduced from 0.6 on HA d ay 1 (HA1) to 0.1 during RA (p < 0.05). Four subjects were ''sick'' (A MS-C > 0.7) during HA1, while only one was ''sick'' during RA. The % o xyhemoglobin, hemoglobin concentration and hematocrit were higher duri ng RA compared to HA1. Conclusions: These results suggest that the ret ention of acclimatization after 8 d at low altitude is sufficient to a ttenuate AMS upon reinduction to high altitude.