THE POSITION OF THE OXYGEN DISSOCIATION CURVE OF HUMAN BLOOD AT HIGH ALTITUDE

Abstract

The position of the oxygen dissociation curve of whole arterial blood was studied on 10 men at 6 levels of altitude, from sea level to 6,140 m., over a period of 2-31/2 months at high altitude. At constant pH of the cells there was no tendency toward an increased affinity of Hb for O but instead there was a uniform tendency in the opposite direction, so that, on the average, at 6,140 m. 3.5 mm. O2 pressure more, than at sea level, were required to produce half saturation. The "physiological" dissociation curves were displaced to the left of sea level up to about 14,000 ft.; above that altitude the curves were displaced increasingly to the right of the sea level positions. The theoretical significance of the observed changes in the fundamental affinity of Hb for O2 is discussed and it is shown that they may be considered to be advantageous at high altitude in that they provide for an increased delivery of oxygen to the tissues at all except values for venous saturation close to zero and arterial saturation lower than about 65%. Dissociation curves on arterial blood drawn in work gave results similar to those obtained in basal rest. The positions of the dissociation curves were detd. for 11 long-time residents at altitudes up to 5,340 m.; 8 of these men were long accustomed to daily labor at 5,700 m. Both at arterial pH2 and at constant pHc these dissociation curves were, in general, within the normal limits for men at sea level; at constant pHc the average was perhaps slightly to the right. Comparison of the residents with the Expedition members indicated that in both cases there is a tendency to achieve homoeostasis and that alteration in the position of the O2 curve at high altitude may be an intermediate stage in final adaptation.