BloodVolumeChangesduring Three-WeekResidenceat High Altitude

Circulating red blood cell volumes were determined by the carbon monoxide method, and plasma volumes were calculated in four men 20, 29, 71, and 75 years old, and two women 29years of age before, during, and after exposure to an altitude of 3800m. In the four youngest subjects there were early in-creases in hemoglobin concentration during the first days at the stated altitude attributed to decreases in plasma volume. At the same time, hemoglobin concentration decreased and plasma volume increased in the oldest subject. Red cell volumes were slow to change, and it was concluded that 3 weeks or more of exposure to this altitude are required to affect significantly the red cell volume in man. IT HAS LONG been known that one of the early responses to exposure to high altitude is an increase in the hemoglobin concentration of circu-lating blood ([Hb]h). This tends to preserve homeo-stasis in spite of the lowered oxygen tension i