Influence of blood donation on O-2 uptake on-kinetics, peak O-2 uptake and time to exhaustion during severe-intensity cycle exercise in humans

Thatcher, Rhys, et al., 'Influence of blood donation on O-2 uptake on-kinetics, peak O-2 uptake and time to exhaustion during severe-intensity cycle exercise in humans', Experimental Physiology (2006) 91(3) pp.499-509 RAE2008

We hypothesized that the reduction of O2-carrying capacity caused by the withdrawal of 450 ml blood would result in slower phase II O2 uptake kinetics, a lower and a reduced time to exhaustion during severe-intensity cycle exercise. Eleven healthy subjects (mean ?S.D. age 23 ? 6 years, body mass 77.2 ? 11.0 kg) completed ?step? exercise tests from unloaded cycling to a severe-intensity work rate (80% of the difference between the predetermined gas exchange threshold and the ) on two occasions before, and 24 h following, the voluntary donation of 450 ml blood. Oxygen uptake was measured breath-by-breath, and kinetics estimated using non-linear regression techniques. The blood withdrawal resulted in a significant reduction in haemoglobin concentration (pre: 15.4 ? 0.9 versus post: 14.7 ? 1.3 g dl?1; 95% confidence limits (CL): ?0.04, ?1.38) and haematocrit (pre: 44 ? 2 versus post: 41 ? 3%; 95% CL: ?1.3, ?5.1). Compared to the control condition, blood withdrawal resulted in significant reductions in (pre: 3.79 ? 0.64 versus post: 3.64 ? 0.61 l min?1; 95% CL: ?0.04, ? 0.27) and time to exhaustion (pre: 375 ? 129 versus post: 321 ? 99 s; 95% CL: ?24, ?85). However, the kinetic parameters of the fundamental response, including the phase II time constant (pre: 29 ? 8 versus post: 30 ? 6 s; 95% CL: 5, ?3), were not altered by blood withdrawal. The magnitude of the slow component was significantly reduced following blood donation owing to the lower attained. We conclude that a reduction in blood O2-carrying capacity, achieved through the withdrawal of 450 ml blood, results in a significant reduction in and exercise tolerance but has no effect on the fundamental phase of the on-kinetics during severe-intensity exercise.

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