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Phlebotomy eliminates the maximal cardiac output response to six weeks of exercise training

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AJP Regulatory Integrative and Comparative Physiology

Published online on

Abstract

With this study we tested the hypothesis that six weeks of endurance training increases maximal cardiac output (Qmax) relatively more by elevating blood volume (BV) than by inducing structural and functional changes within the heart. Nine healthy but untrained volunteers (VO2max 47 ± 5 ml.min-1.kg-1) underwent supervised training (60 min; 4 times weekly at 65% VO2max for six weeks) and Qmax was determined by inert gas re-breathing during cycle ergometer exercise before and after the training period. After the training period, blood volume (determined in duplicates by CO re-breathing) was re-established to pre-training values by phlebotomy and Qmax was quantified again. Resting echography revealed no structural heart adaptations as a consequence of the training intervention. Following the training period, plasma volume (PV), red blood cell volume (RBCV) and BV increased (p<0.05) by 147 ± 168 (5 ± 5 %), 235 ± 64 (10 ± 3 %) and 382 ± 204 ml (7 ± 4 %), respectively. VO2max was augmented (p<0.05) by 10 ± 7 % following the training period and decreased (p<0.05) by 8 ± 7 % with phlebotomy. Concomitantly, Qmax was increased (p<0.05) from 18.9 ± 2.1 to 20.4 ± 2.3 l.min-1 (9 ± 6 %) as a consequence of the training intervention, and following normalization of BV by phlebotomy Qmax returned to pre training values (18.1 ± 2.5 l.min-1; 12 ± 5 % reversal). Thus, the exercise training induced increase in BV is the main mechanism increasing Qmax following six weeks of endurance training in previously untrained subjects.