Altitude acclimatization and blood volume: effects of exogenous erythrocyte volume expansion

Abstract

We studied sea-level residents during 13 days of altitude acclimatization to determine 1) altitude acclimatization effects on erythrocyte volume and plasma volume, 2) if exogenous erythrocyte volume expansion alters subsequent erythrocyte volume and plasma volume adaptations, 3) if an increased blood oxygen content alters erythropoietin responses during altitude acclimatization, and 4) mechanisms responsible for plasma loss at altitude. Sixteen healthy men had a series of hematologic measurements made at sea level, on the first and ninth days of altitude (4,300 m) residence, and after returning to sea level. Twenty-four hours before the ascent to altitude, one group received a 700-ml infusion of autologous erythrocytes (42% hematocrit), whereas the other group received only a saline infusion. Erythrocyte infusion increased erythrocyte volume by approximately 10%, whereas saline infusion had no effect; in addition, initially at altitude, blood oxygen content was 8% higher in erythrocyte-infused than in saline-infused subjects. The new findings regarding altitude acclimatization are summarized as follows: 1) erythrocyte volume does not change during the first 13 days and is not affected by prior exogenous expansion, 2) a modest increase in blood oxygen content does not modify erythropoietin responses, 3) plasma losses are related to vascular protein losses, and 4) exogenous erythrocyte volume expansion coincides with transient increases in plasma loss, vascular protein loss, and mean arterial pressure elevation. These findings better define human blood volume responses during altitude acclimatization.

Short-Term Arrival Strategies for Endurance Exercise Performance at Moderate Altitude

“…Sawka and others (1996) found that erythrocyte volume did not change after 13-days of continuous high altitude exposure and that plasma volume decreased by around 10%. 82 Other studies have shown similar results. [83][84][85][86] An adequate plasma volume is quite necessary for cardiac function during maximal exercise and to ensure that blood can be properly transported throughout the circulatory system.…”

“…In the Sawka (1996) study, fluid intake was controlled to prevent dehydration and the weight loss observed was not nearly enough to account for the volume loss seen in the plasma. 82 This study showed for the first time that decreases in plasma oncotic pressures and fluid volume were strongly correlated. He suggests that initially this is due to increased capillary permeability, possibly followed later by an increase in protein degradation.…”

Physical activity at moderate and high altitudes. Cardiovascular and respiratory morbidit

“…The physiological mechanisms are the following: 1) increase in the pulmonary ventilation 39 ; 2) reduction in the HR previously increased in the acute response 22,39 ; 3) decrease in the plasmatic volume 39,40 ; 4) reduction of the accumulation of lactate in the blood during submaximal exercise in relation to the more elevated levels of acute response 39 ; 5) improvement of the cardiorespiratory capacity for exercise, also related to the initial exposure to the hypobaric hypoxia 23,41 ; 6) increase in the secretion of renal erythropoietin, in the hemoglobin mass and in the hematocrit 34,36,37,42 .…”

Effects of Intermittent Altitude Exposures on Acclimatization of 4,300 M

“…Physiological variables that contribute to the increase in submaximal endurance capacity with altitude acclimatization include an increase in exercise minute ventilation (VE) (21,77) and decrease in plasma volume (PV) (39,96,101,113). These changes cause respective increases in arterial oxygen saturation (Sa0 2 ) and hemoglobin concentration ([Hb]).…”

“…These changes cause respective increases in arterial oxygen saturation (Sa0 2 ) and hemoglobin concentration ([Hb]). The increase in [Hb] occurs primarily due to a decrease in PV since red blood cell mass and erythropoietin concentration ([EPO]) are not increased after a 2-3 wk altitude acclimatization period (61,96). Since arterial oxygen content (Ca0 2 ) is determined by both Sa0 2 and [Hb], Ca0 2 is reduced upon initial ascent to altitude, due to the lower partial pressure of arterial oxygen (Pa0 2 ), and increased with altitude acclimatization (35).…”