Nitrogen washout studies in acute mountain sickness.

We assessed the severity of Acute Mountain Sickness (A.M.S.), indices of pulmonary gas exchange and nitrogen washout curves in healthy volunteers acutely exposed to high altitude. Symptoms of A.M.S. ranged from malaise to vomiting with intractable headache. The slope of phase III of the nitrogen washout curve increased most in those subjects with the most severe A.M.S. and who were most hypoxemic. The sickest subject also had the greatest increase in (A-a)DO2 and the largest increase in the slope of phase III. These abnormalities in gas exchange and nitrogen washout curves in the subjects with the most marked A.M.S. suggest that the manifestations of cerebral and pulmonary dysfunction at altitude develop simultaneously, although not necessarily by identical mechanisms.