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Am J Physiol Heart Circ Physiol (March 13, 2009). doi:10.1152/ajpheart.01223.2008
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Submitted on November 20, 2008
Revised on February 27, 2009
Accepted on February 28, 2009

Transfer function characteristics of the neural and peripheral arterial baroreflex arcs at rest and during post exercise muscle ischemia in humans

Shigehiko Ogoh1*, James P Fisher2, Colin N. Young3, Peter B. Raven1, and Paul J. Fadel3

1 University of North Texas Health Science Center
2 University of Birmingham
3 University of Missouri

* To whom correspondence should be addressed. E-mail: sogoh{at}hsc.unt.edu.

Previous studies have demonstrated an increase in the arterial baroreflex (ABR) control of muscle sympathetic nerve activity (MSNA) during isolated activation of the muscle metaboreflex with post exercise muscle ischemia (PEMI). However, the increased ABR-MSNA control does not appear to manifest in an enhancement in the ABR control of arterial blood pressure (BP), suggesting alterations in the transduction of MSNA into a peripheral vascular response and a subsequent ABR-mediated change in BP. Thus, we examined the operating gains of the neural and peripheral arcs of the ABR and their interactive relationship at rest and during muscle metaboreflex activation. In nine healthy subjects, graded isolation of the muscle metaboreflex was achieved by PEMI following isometric handgrip performed at 15 and 30% maximal voluntary contraction (MVC). To obtain the sensitivities of the ABR neural and peripheral arcs, the transfer function gain from BP to MSNA and MSNA to femoral vascular conductance, respectively were analyzed. No changes from rest were observed in the ABR neural or peripheral arcs during PEMI after 15%MVC handgrip. However, PEMI following 30%MVC handgrip increased the low frequency (LF) transfer function gain between BP and MSNA (ABR neural arc; +58±28%, P=0.036), whereas the LF gain between MSNA and femoral vascular conductance (ABR peripheral arc) was decreased from rest (-36±8%, P=0.017). These findings suggest that during high intensity muscle metaboreflex activation an increased ABR gain of the neural arc appears to offset an attenuation of the peripheral arc gain to help maintain the overall ABR control of systemic blood pressure.







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