Elliott, Adrian (2013) Defining the haemodynamic response to maximal exercise using novel beat-to-beat measurement methods. (PhD thesis), Kingston University, .
Abstract
Strenuous exercise presents a significant challenge to the cardiovascular system, such that it is widely assumed that the heart largely governs short, high-intensity aerobic exercise performance. Despite considerable investigation of this topic, the haemodynamic responses to maximal exercise are still not well understood, mostly due to insufficient measurement methods unable to quantify the beat-to-beat response of the cardiovascular system during dynamic exercise. In this thesis, two novel approaches (bioreactance and pulse contour analysis calibrated by lithium dilution) for the continuous assessment of exercise haemodynamics in a healthy, trained population were evaluated. In study I, bioreactance was found to considerably underestimate cardiac output (Q) in comparison with contemporaneous measurements with inert gas rebreathing. In studies II and III, we evaluated pulse contour analysis, calibrated by lithium indicator dilution. Our findings indicated that the timing of calibration was central to the accuracy of measurements made during exercise using this method, perhaps due to alterations in vascular compliance throughout exercise'. In study IV, optimising the calibration of this method during exercise permitted the evaluation of the haemodynamic response to maximal and supramaximal (10% greater than maximal) exercise on a beat-to-beat basis, with the finding that cardiac power output, a measure of cardiac work, was higher during supramaximal exercise despite a similar Q and oxygen consumption (V02) between the two workloads. This finding is important for the understanding of factors limiting exercise performance for it indicates that there is cardiac functional reserve at exhaustion during testing for V02max, thus indicating that the heart is unlikely to be responsible for the termination of exercise as it can be considered to be working submaximally.
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