ACUTE MOUNTAIN-SICKNESS - INCREASED SEVERITY DURING SIMULATED ALTITUDE COMPARED WITH NORMOBARIC HYPOXIA

Acute mountain sickness (AMS) strikes those in the mountains who go to o high too fast. Although AMS has been long assumed to be due solely t o the hypoxia of high altitude, recent evidence suggests that hypobari a may also make a significant contribution to the pathophysiology of A MS. We studied nine healthy men exposed to simulated altitude, normoba ric hypoxia, and normoxic hypobaria in an environmental chamber for 9 h on separate occasions. To simulate altitude, the barometric pressure was lowered to 432 +/- 2 (SE) mmHg (simulated terrestrial altitude 4, 564 m). Normobaric hypoxia resulted from adding nitrogen to the chambe r (maintained near normobaric conditions) to match the inspired Po-2 o f the altitude exposure. By lowering the barometric pressure and addin g oxygen, we achieved normoxic hypobaria with the same inspired Po, as in our laboratory at normal pressure. AMS symptom scores (average sco res from 6 and 9 h of exposure) were higher during simulated altitude (3.7 +/- 0.8) compared with either normobaric hypoxia (2.0 +/- 0.8; P < 0.01) or normoxic hypobaria (0.4 +/- 0.2; P < 0.01). in conclusion, simulated altitude induces AMS to a greater extent than does either no rmobaric hypoxia or normoxic hypobaria: although normobaric hypoxia in duced some AMS.