Limb congestion enhances the synchronization of sympathetic outflow with muscle contraction.
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 <0.005; limb congestion main effect P = 0.054). These changes in the distribution of signal-averaged MSNA were seen despite the fact that the mean number of sympathetic discharges did not increase over baseline. We conclude that synchronization of contraction and MSNA is seen during short repetitive bouts of handgrip. The sensitizing effect of contraction time and limb congestion are apparently due to feedback from muscle afferents within the exercising muscle.
Division of Cardiology, The Pennsylvania State University College of Medicine, The Milton S. Hershey Medical Center, Hershey 17033,USA.
S
S
Mostoufi-Moab
M D
MD
Herr
D H
DH
Silber
K S
KS
Gray
U A
UA
Leuenberger
L I
LI
Sinoway
D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D015444:Exercise / Q000502:physiology; D005542:Forearm / Q000098:blood supply*; D018737:Hand Strength / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D009132:Muscles / Q000098:blood supply; D010507:Periodicity; D012039:Regional Blood Flow / Q000502:physiology; D013564:Sympathetic Nervous System / Q000502:physiology*; D013997:Time Factors; D014680:Veins / Q000502:physiology