Effects of acute plasma volume expansion on altering exercise-heat performance

To determine the effect an acute plasma volume expansion has on body temperature responses and exercise performance in the heat, seven unacclimatized male volunteers attempted to complete two 90-min walks (45% of \(\dot VO_2 \) max) in a hot/dry (45‡ C/20% rh) environment. The experimental walk was preceded by an infusion of human albumin (50 g in a 200-ml solution) and the control walk was preceded by an infusion of isotonic saline (200 ml). Saline infusion did not alter the plasma volume. The albumin infusion was found to significantly (p<0.01) increase plasma volume ~ 13% over control levels. No significant differences were found for performance time, final heart rate or final rectal temperature values between the two walks. In general, significant differences were not found for systolic blood pressure, rectal temperature, mean skin temperature, heat storage, sweat rate, plasma lactate, plasma osmolality, or plasma protein content values between the two walks. However, heart rate responses were found to be significantly lower (p<0.05; ~ 13 bt·min⁻¹) during the 25-min and 40-min measurements of the experimental walk. These data suggest that plasma volume expansion may be a supportive adaptation to enable lowered heart rate responses but does not improve thermoregulatory function or performance time in the heat.