Influence of blood donation on oxygen uptake kinetics during moderate and heavy intensity cycle exercise.

The purpose of this study was to determine the effects of a reduced whole body blood volume on the kinetic response of VO(2) during moderate and heavy intensity exercise. Six males and four females (age, 21+/-2 yrs; height, 175.2+/-5.1 cm; weight, 66.4+/-2.8 kg; VO(2)max, 53.0+/-4.1 ml x kg (-1) x min(-1)), completed a square-wave cycling ramp test to determine ventilatory threshold (VT) and VO(2max). Kinetics trials were completed 24 h pre and post donation of 450 cm (3) of blood. The kinetics trials were moderate intensity (80%VT) and heavy intensity (Delta50% VT - VO(2max)). Breath-by-breath gas exchange, heart rate, blood pressure, haemoglobin O(2) saturation, and blood [lactate] were measured throughout the trials. Post-donation haemoglobin, haematocrit and erythrocyte count were all significantly reduced (p<or= 0.05). Blood donation caused a significant increase in resting heart rate (P<or= 0.05). There were non-significant differences in the time constants or amplitude of phase II VO(2) kinetics in either moderate or heavy exercise (p>or= 0.05), or in the amplitude of the slow component. The capacity of the cardiovascular system to meet the metabolic demands of skeletal muscle at the onset of exercise does not limit the oxygen uptake.