The effect of altitude pre-acclimatization on acute mountain sickness during reexposure.
BACKGROUND
Acclimatization to high altitude appears to prevent acute mountain sickness (AMS), as evidenced by a decline in AMS symptoms as acclimatization progresses.


OBJECTIVE
We hypothesized that partial retention of acclimatization would attenuate the incidence and/or severity of AMS upon reinduction to altitude.


METHODS
To test this hypothesis 6 male lowlanders returned to sea level after the acclimatizing of the 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 daily administration of the Environmental Symptoms Questionnaire during HA and RA.


RESULTS
The mean AMS-C scores were reduced from 0.6 on HA day 1 (HA1) to 0.1 during RA (p < 0.05). Four subjects were "sick" (AMS-C > 0.7) during HA1, while only one was "sick" during RA. The % oxyhemoglobin, hemoglobin concentration and hematocrit were higher during RA compared to HA1.


CONCLUSIONS
These results suggest that the retention of acclimatization after 8 d at low altitude is sufficient to attenuate AMS upon reinduction to high altitude.
Altitude Physiology and Medicine Division, U.S. Army Research Institute of Environmental Medicine, Natick, MA 01760, USA.
T P
TP
Lyons
S R
SR
Muza
P B
PB
Rock
A
A
Cymerman
D000064:Acclimatization / Q000502:physiology*; D000208:Acute Disease; D000328:Adult; D000531:Altitude; D000532:Altitude Sickness / Q000097:blood / Q000503:physiopathology / Q000517:prevention & control*; D004781:Environmental Exposure; D006400:Hematocrit; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D015994:Incidence; D008297:Male; D012008:Recurrence; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires
D006454:Hemoglobins