Received September 2, 2005
Revised September 23, 2005
Accepted after revision October 27, 2005

¹ University of Texas Southwestern Medical Center at Dallas
² University of Missouri School of Medicine
³ Copenhagen Muscle Research Centre
⁴ University of Calgary
⁵ Copenhagen Muscle Research Center
⁶ University of North Texas Health Science Center at Fort Worth

^* To whom correspondence should be addressed. E-mail: kevin.gallagher{at}utsouthwestern.edu.

	Abstract

Central command and the exercise pressor reflex can independently reset the carotid baroreflex (CBR) during exercise. The present investigation assessed the interactive relationship between these two neural mechanisms in mediating baroreflex resetting during exercise. Six men performed static leg exercise at 20% maximal voluntary contraction under four conditions: control, no perturbation; neuromuscular blockade (NMB), administration of the neuromuscular blocking agent Norcuron (central command activation); MAST, application of medical anti-shock trousers inflated to 100 Torr (exercise pressor reflex activation); and combo, NMB plus MAST (concomitant central command and exercise pressor reflex activation). In regard to CBR control of heart rate (HR), both NMB and combo conditions resulted in a further resetting of the carotid-cardiac stimulus-response curve compared to control suggesting that CBR-HR resetting is predominately mediated by central command. In contrast, it appears that CBR control of blood pressure can be mediated by signals from either central command or the exercise pressor reflex as both NMB and MAST conditions equally augmented the resetting of the carotid-vasomotor stimulus-response curve. In regard to the regulation of both HR and blood pressure, the extent of CBR resetting was greater during the combo condition than during over activation of either central command or the exercise pressor reflex alone. Therefore, we suggest that central command and the exercise pressor reflex interact such that signals from one input facilitate signals from the other resulting in an enhanced resetting of the baroreflex during exercise.

Key Words: Baroreceptor, Blood pressure, Isometric exercise

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