Abstract
Four subjects were studied before and during a 16-day space flight. The test included 2min of rest, 2min of sustained handgrip (SHG), and 2min of post-exercise circulatory occlusion (PECO). Heart rate (HR) and mean arterial pressure (MAP) responses to central command and mechanoreceptor stimulation were determined from the difference between SHG and PECO. Responses to metaboreceptor stimulation were determined from the difference between PECO and rest. Late in-flight (days 12-14) the central command/mechanoreceptor component of the HR response was reduced by 5bpm (P=0.01) from its pre-flight value of 15 (+/-3)bpm (mean (+/-SEM)). At the same time the metaboreflex responses of HR and MAP were unchanged. The attenuated HR response to central command was likely of baroreflex origin. Together with a parallel study of PECO after dynamic leg exercise, our data indicate that central processing of metaboreflex inputs is unchanged in microgravity whereas metaboreflex inputs from weight-bearing muscles are enhanced.
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