Autonomic nervous control of heart rate during blood-flow restricted exercise in man
Summary Power spectra of instantaneous heart rate ( f c ) allows the estimation of the contribution of sympathetic and parasympathetic control of f c during steady-state conditions. The present study was designed to examine autonomic control of f c as influenced by normal dynamic leg exercise and by ischemic leg exercise. Eight subjects performed supine cycle ergometry at 30% of their control peak work rate, with and without blood-flow restriction. Blood-flow restriction was induced by exposing the exercising legs to a supra-atmospheric pressure of 6.7 kPa (leg positive pressure; LPP). The exercise responses of arterial pressure and f c increased ( P f c , as indicated by a decrease ( P f c increased, as indicated by an increase ( P P f c associated with normal dynamic exercise was mediated predominantly by parasympathetic withdrawal, whereas the exaggerated f c response during ischemic exercise resulted from a combination of cardiac sympathetic drive and parasympathetic withdrawal. The increase in sympathetic activity is attributable to a muscle chemoreflex drive, which also may have attenuated parasympathetic activity by reciprocal inhibition. Alternatively, augmented central command mediated parasympathetic withdrawal during ischemic exercise.
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