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Am J Physiol Heart Circ Physiol (March 7, 2008). doi:10.1152/ajpheart.91497.2007
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Submitted on December 19, 2007
Revised on March 5, 2008
Accepted on March 5, 2008

Effect of Muscle Metaboreflex Activation on Carotid-Cardiac Baroreflex Function in Humans

James P Fisher1, Colin N Young, and Paul J Fadel2*

1 University of Missouri-Columbia
2 University of Missouri

* To whom correspondence should be addressed. E-mail: fadelp{at}health.missouri.edu.

Whether activation of metabolically-sensitive skeletal muscle afferents (i.e., muscle metaboreflex) influences cardiac baroreflex responsiveness remains incompletely understood. A potential explanation for contrasting findings of previous reports may be related to differences in the magnitude of muscle metaboreflex activation utilized. Therefore, the present study was designed to investigate the influence of graded intensities of muscle metaboreflex activation on cardiac baroreflex function. In eight healthy subjects (24±1 yrs), graded isolation of the muscle metaboreflex was achieved by post exercise ischemia (PEI) following moderate (PEI-M) and high (PEI-H) intensity isometric handgrip performed at 35% and 45% maximum voluntary contraction, respectively. Beat-to-beat heart rate (HR) and blood pressure were measured continuously. Rapid pulse trains of neck pressure and neck suction (+40 to -80 Torr) were applied to derive carotid baroreflex stimulus-response curves. Mean blood pressure increased significantly from rest during PEI-M (+13±3 mmHg) and was further augmented during PEI-H (+26±4 mmHg) indicating graded metaboreflex activation. However, the operating point gain and maximal gain (-0.51±0.09, -0.48±0.13 and -0.49±0.12 b•min-1•mmHg-1 for rest, PEI-M and PEI-H) of the carotid-cardiac baroreflex function curve were unchanged from rest during PEI-M and PEI-H (P>0.05 vs. rest). Further, the carotid-cardiac baroreflex function curve was progressively reset rightwards from rest to PEI-M to PEI-H, with no upward resetting. These findings suggest that the muscle metaboreflex contributes to the resetting of the carotid baroreflex control of HR; however, it would appear not to influence carotid-cardiac baroreflex responsiveness in humans even with high intensity activation during PEI.




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Am. J. Physiol. Heart Circ. Physiol.Home page
S. Ogoh, J. P. Fisher, C. N. Young, P. B. Raven, and P. J. Fadel
Transfer function characteristics of the neural and peripheral arterial baroreflex arcs at rest and during postexercise muscle ischemia in humans
Am J Physiol Heart Circ Physiol, May 1, 2009; 296(5): H1416 - H1424.
[Abstract] [Full Text] [PDF]




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