S. Mostoufi-moab et al., Limb congestion enhances the synchronization of sympathetic outflow with muscle contraction, AM J P-REG, 279(2), 2000, pp. R478-R483
Citations number
27
Categorie Soggetti
Physiology
Journal title
AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY INTEGRATIVE AND COMPARATIVE PHYSIOLOGY
In this report, we examined if the synchronization of muscle sympathetic ne
rve activity (MSNA) with muscle contraction is enhanced by limb congestion.
To explore this relationship, we applied signal-averaging techniques to th
e MSNA signal obtained during short bouts of forearm contraction (2-s contr
action/ 3-s rest cycle) at 40% maximal voluntary contraction for 5 min. We
performed this analysis before and after forearm venous congestion; an inte
rvention that augments the autonomic response to sustained static muscle co
ntractions via a local effect on muscle afferents. There was an increased p
ercentage of the MSNA noted during second 2 of the 5-s contraction/ rest cy
cles. The percentage of total MSNA seen during this particular second incre
ased from minute 1 to 5 of contraction and was increased further by limb co
ngestion (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 mai
n effect <0.005; limb congestion main effect P = 0.054). These changes in t
he distribution of signal-averaged MSNA were seen despite the fact that the
mean number of sympathetic discharges did not increase over baseline. We c
onclude that synchronization of contraction and MSNA is seen during short r
epetitive bouts of handgrip. The sensitizing effect of contraction time and
limb congestion are apparently due to feedback from muscle afferents withi
n the exercising muscle.