| Abstrakt: |
Our objectives were firstly, to study the patterns of the cardiac output (Q?) and the arteriovenous oxygen difference [(a-v¯)O2] responses to oxygen uptake (V?O2) during constant workload exercise (CWE) performed above the respiratory compensation point (RCP), and secondly, to establish the relationships between their kinetics and the time to exhaustion. Nine subjects performed two tests: a maximal incremental exercise test (IET) to determine the maximalV?O2 (V?O2peak), and a CWE test to exhaustion, performed atp?50 (intermediate power between RCP andV?O2peak). During CWE,V?O2 was measured breath-by-breath,Q?was measured beat-by-beat with an impedance device, and blood lactate (LA) was sampled each minute. To calculate (a-v¯)O2, the values ofV?O2 andQ?were synchronised over 10 s intervals. A fitting method was used to describe theV?O2,Q?and (a-v¯)O2 kinetics. The (a-v¯)O2 difference followed a rapid monoexponential function, whereas bothV?O2 andQ?were best fitted by a single exponential plus linear increase: the time constant (t)V?O2 [57 (20 s)] was similar to t (a-v¯)O2, whereas t forQ?was significantly higher [89 (34) s,P<0.05] (values expressed as the mean and standard error). LA started to increase after 2 min CWE then increased rapidly, reaching a similar maximal value as that seen during the IET. During CWE, the rapid component of V?O2 uptake was determined by a rapid and maximal (a-v¯)O2 extraction coupled with a two-fold longerQ?increase. It is likely that lactic acidosis markedly increased oxygen availability, which when associated with the slow linear increase ofQ?, may account for theV?O2 slow component. Time to exhaustion was larger in individuals with shorter time delay for (a-v¯)O2 and a greater t forQ?. [ABSTRACT FROM AUTHOR] |
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