ALTITUDE ACCLIMATIZATION AND BLOOD-VOLUME - EFFECTS OF EXOGENOUS ERYTHROCYTE VOLUME EXPANSION

We studied sea-level residents during 13 days of altitude acclimatizat ion to determine 1) altitude acclimatization effects on erythrocyte vo lume and plasma volume, 2) if exogenous erythrocyte volume expansion a lters subsequent erythrocyte volume and plasma volume adaptations, 3) if an increased blood oxygen content alters erythropoietin responses d uring altitude acclimatization, and 4) mechanisms responsible for plas ma loss at altitude. Sixteen healthy men had a series of hematologic m easurements made at sea level, on the first and ninth days of altitude (4,300 m) residence, and after returning to sea level. Twenty-four ho urs before the ascent to altitude, one group received a 700-ml infusio n of autologous erythrocytes (42% hematocrit), whereas the other group received only a saline infusion. Erythrocyte infusion increased eryth rocyte volume by similar to 10%, whereas saline-infusion had no effect ; in addition, initially at altitude, blood oxygen content was 8% high er in erythrocyte-infused than in saline-infused subjects. The new fin dings regarding altitude acclimatization are summarized as follows: 1) erythrocyte volume does not change during the first 13 days and is no t affected by prior exogenous expansion, 2) a modest increase in blood oxygen content does not modify erythropoietin responses, 3) plasma lo sses are related to vascular protein losses, and 4) exogenous erythroc yte volume expansion coincides with transient increases in plasma loss , vascular protein loss, and mean arterial pressure elevation. These f indings better define human blood volume responses during altitude acc limatization.