Acute plasma volume expansion alters cardiovascular but not thermal function during moderate intensity prolonged exercise

To investigate the hypothesis that the increase in plasma volume (PV) that typically occurs with training results in improved cardiovascular and thermal regulation during prolonged exercise, eight untrained males (V(O2)peak = 3.52 +/- 0.12 L x min(-1)) performed 90 min of cycle ergometry at 62% V(O2)peak before and after acute PV expansion. Subjects were infused with a PV-expanding solution (dextran (6%) or Pentaspan (10%)) equivalent to 6.7 mL x kg(-1) body mass (PVX) or acted as their own control (CON) in a randomized order. PVX resulted in a calculated 15.8% increase in resting PV, which relative to CON, was maintained throughout the exercise (P < 0.05). During PVX, heart rate was lower (P < 0.05) and stroke volume and cardiac output were higher (P < 0.05) during the exercise. Mean arterial pressure and total peripheral resistance, although altered by exercise (P < 0.05), were not different between the two conditions. Core temperature, which was progressively increased by the exercise (P < 0.01), was not affected by PVX. A similar decrease in body weight was observed between the conditions as a result of the exercise (P < 0.01). These results indicate that acute PVX alters cardiovascular performance without affecting the thermoregulatory response to prolonged cycle exercise.