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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
Author(s) -
Burnley Mark,
Roberts Claire L.,
Thatcher Rhys,
Doust Jonathan H.,
Jones Andrew M.
Publication year - 2006
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2005.032805
Subject(s) - intensity (physics) , chemistry , confidence interval , zoology , kinetics , blood pressure , medicine , endocrinology , biology , physics , quantum mechanics
We hypothesized that the reduction of O 2 ‐carrying capacity caused by the withdrawal of ∼450 ml blood would result in slower phase II O 2 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 O 2 ‐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.