Acute hypervolemia, cardiac performance, and aerobic power during exercise

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Abstract
The relative importance of blood volume (BV) for the maximum aerobic power (.ovrhdot.VO2 max [maximum O2 uptake]) was evaluated in healthy men by sequential measurements without intervention under 2 conditions: after hemodilution with a plasma expander, thus increasing BV but keeping red cell mass constant and lowering Hb concentration [Hb]; and after whole blood withdrawal, which restored BV to control conditions but reduced red cell mass and [Hb] to equal conditions as under the 1st situation. After BV expansion (average 700 ml), an unchanged .ovrhdot.VO2 max were found as compared to control data despite lowered [Hb]. Cardiac output (.ovrhdot.Q) was increased after BV expansion at rest and during all exercise levels (maximum 27.4 and 29.5 l.cntdot.min-1, respectively). Peak stroke volume was increased from 144 to 173 ml. Arterial blood pressures were unchanged or lowered. After blood-letting to a similar [Hb], a significantly reduced .ovrhdot.VO2 max was found. There is a significant influence of the size of the blood volume on cardiac performance. The increased .ovrhdot.Qmax is discussed in relation to preload, inotropic state, heart rate and afterload. Plasma volume expansion causes increased preload which may explain this primary effect on the central circulation (Frank-Starling effect).