Acute plasma volume expansion alters cardiovascular but not thermal function during moderate intensity prolonged exercise B.D. Roy, H.J. Green, S.M. Grant, and M.A. Tarnopolsky Abstract: 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 ( VO 2 peak = 3.52 ± 0.12 L·min –1 ) performed 90 min of cycle ergometry at 62% VO 2 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·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. Key words: cardiovascular, prolonged exercise, acute plasma volume expansion, thermoregulation, hypervolemia. Résumé : On a examiné l’hypothèse que l’augmentation de volume plasmatique (VP) qui se produit habituellement durant l’entraînement améliore la régulation thermique et cardio-vasculaire pendant un exercice prolongé. À cet effet, huit hommes non entraînés ( VO 2 max = 3,52 ± 0,12 L·min –1 ) ont été soumis à un exercice sur cycloergomètre pendant 90 min à une VO 2 max de 62%, avant et après une expansion aiguë du VP. Les sujets ont reçu une perfusion d’une solution qui augmente le VP (dextran (6%) ou Pentaspan (10%)), équivalant à 6,7 mL·kg –1 de masse corporelle (XVP), ou ont servi de témoins (TÉM) dans un ordre aléatoire. La XVP a induit une augmentation de 15,8% du VP au repos comparativement à la valeur TÉM; cette augmentation s’est maintenue pendant toute la durée de l’exercice (P < 0,05). La fréquence cardiaque a été plus faible (P < 0,05) durant la XVP et les débits systolique et cardiaque ont été plus élevés (P < 0,05) durant l’exercice. La pression artérielle moyenne et la résistance périphérique totale, bien que modifiées par l’exercice (P < 0,05), n’ont pas différé dans les deux protocoles. La température centrale, qui a graduellement augmenté pendant l’exercice (P < 0,01), n’a pas été influencée par la XVP. L’exercice a entraîné une diminution similaire de poids corporel dans les deux protocoles (P < 0,01). Ces résultats indiquent que la XVP aiguë modifie la performance cardio-vasculaire sans influencer la réponse thermorégulatrice à un exercice prolongé sur bicyclette. Mots clés : cardio-vasculaire, exercice prolongé, expansion aiguë du volume plasmatique, thermorégulation, hypervolémie. [Traduit par la Rédaction] Roy et al. 250 Introduction One of the most precocious adaptations observed with prolonged exercise training in the unaccustomed individual is an increase in plasma volume (PV). Depending on the ex- ercise and environmental conditions employed, the increase in PV may exceed 20% within the first few days of regular exercise (Green et al. 1987; Senay et al. 1976). Interestingly, training is also accompanied by changes in the cardiovascu- lar response to short-term, submaximal steady-state exercise. At the same submaximal absolute power output, these adap- tations have been typically represented as an increase in stroke volume (SV) and a decrease in heart rate (HR) with unchanged cardiac output ( Q) and oxygen consumption ( V O 2 ) (Rowell et al. 1996). Mean arterial blood pressure (MAP) and total peripheral resistance (TPR) also appear unaltered by the training (Rowell et al. 1996; Convertino 1991). Collectively, these training responses are believed to display their most important consequences during prolonged sub- maximal exercise by providing for improved cardiovascular 244 Can. J. Physiol. Pharmacol. 78: 244–250 (2000) © 2000 NRC Canada Received April 23, 1999. B.D. Roy, H.J. Green, and S.M. Grant. 1 Department of Kinesiology, University of Waterloo, Waterloo, ON N2L 3G1, Canada. M.A. Tarnopolsky. Department of Kinesiology and Medicine, McMaster University, Hamilton, ON L8S 4K1, Canada. 1 Author for correspondence (e-mail: green@healthy.uwaterloo.ca).