Limb congestion enhances the synchronization of sympathetic outflow with muscle contraction

1 Division of Cardiology, The Pennsylvania State University College of Medicine, The Milton S. Hershey Medical Center, Hershey 17033; and 2 Lebanon Veterans Affairs Medical Center, Lebanon, Pennsylvania 17042 In this report, we examined if the synchronization of muscle sympathetic nerve activity (MSNA) with muscle contraction is enhanced by limb congestion. To explore this relationship, we applied signal-averaging techniques to the MSNA signal obtained during short bouts of forearm contraction (2-s contraction/3-s rest cycle) at 40% maximal voluntary contraction for 5 min. We performed this analysis before and after forearm venous congestion; an intervention that augments the autonomic response to sustained static muscle contractions via a local effect on muscle afferents. There was an increased percentage of the MSNA noted during second 2 of the 5-s contraction/rest cycles. The percentage of total MSNA seen during this particular second increased from minute 1 to 5 of contraction and was increased further by limb congestion (control minute 1 = 25.6 ± 2.0%, minute 5 = 32.8 ± 2.2%; limb congestion minute 1 = 29.3 ± 2.1%, minute 5 = 37.8 ± 3.9%; exercise main effect