The role of spontaneous bursts of muscle sympathetic nerve activity in mediating peripheral vascular responses and cardiovascular hemodynamics in resting man
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The ability for sympathetic nerve activity to dynamically evoke vasoconstriction is paramount for the regulation of blood flow and blood pressure. However, very little information is available to characterize the influence of spontaneously occurring sympathetic nerve activity on human blood vessels during rest. We employed spike-triggered averaging to assess the systematic influence of resting muscle sympathetic nerve activity (MSNA) bursts to determine: 1) their influence on leg and forearm vascular conductance as well as on conduit artery diameter in resting young healthy men. We demonstrate that spontaneous MSNA bursts exert a robust and dynamic vasoconstrictor influence on forearm and leg skeletal muscle blood resistance arteries that occur in close association with vasoconstriction of the systemic vasculature, to subsequently increase arterial blood pressure during rest. Vasoconstriction was greater in leg resistance arteries compared to that observed in the forearm, and conduit arteries did not exhibit any decreases in diameter following spontaneous MSNA bursts. Variations in the amplitude and pattern of MSNA bursts modulated the magnitude of responses via α-adrenergic receptor mechanisms. Collectively, these are the first data to describe the influence of spontaneously occurring MSNA on the human vasculature during rest, suggesting that the dynamic control of skeletal muscle blood flow importantly participates in the control of systemic hemodynamics and blood pressure.
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