Relative contribution of central and peripheral input to cardiovascular regulation during exercise

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In order to determine the relative contribution of central command and reflex control of muscle sympathetic nerve activity (MSNA) to cardiovascular regulation during exercise, we recorded the MSNA using microneurographic technique and the cardiovascular parameters.1) Isometric muscle contraction increased MSNA but the onset of increase in MSNA was delyaed during exercise and the higher MSNA was persisted during ischemia of contracting muscle following exercise. The increase in MSNA may be related predominantly to the muscle metaboreflex rather than the central command. The magnitude of MSNA response was also depended on the contracting muscle groups.2) During maximal voluntary muscle contraction, the onset of MSNA rise was also delayd as seen in isometric muscle contraction and thus indicated a lesser effect of the central command on MSNA.3) Since low intensity cycling (>40% of maximal oxygen uptake) performed for several minutes did not activate MSNA,we tested whether the MSNA increased during prolonged cycling for 30 minutes. The MSNA and body temperature were increased 15 minutes after the commencement of cycling without any increse in blood lactate concentration. These results suggest that the other reflex mechanism besides the metaboreflex is more important than the central command to control cardiovascular system during prolong leg exercise.4) The cardiac sympathetic activity estimated by heart rate variability and MSNA were increased concomitantly during graded cycling. It is considered that the increase in heart rate and sympathetic nerve activity supplying skeletal muscle vasculature might at least in part have the same reflex mechanism.In conclusion, this study will demonstrate that the reflex mechanisms have a more important role to control cardiovascular adaptation during exercise rather than the central command. These reflex mechanisms are modulated by the by the intensity and the duration of exercise, and also the exercising muscle groups.