Received January 31, 2008
Revised March 5, 2008
Accepted after revision April 24, 2008

¹ University of Birmingham

^* To whom correspondence should be addressed. E-mail: rxd117{at}bham.ac.uk.

	Abstract

We examined the effects of muscle mechanoreflex stimulation by passive calf muscle stretch, at rest, and during concurrent muscle metaboreflex activation, on carotid baroreflex (CBR) sensitivity. 12 subjects either performed 1.5min one-legged isometric plantarflexion at 50% maximum voluntary contraction with their right or left calf (two ischaemic exercise (IE) trials, IER and IEL), or rested for 1.5min (two ischaemic control (IC) trials, ICR and ICL). Following exercise, blood pressure elevation was partially maintained by local circulatory occlusion (CO). 3.5min of CO was followed by 3min of CO with passive stretch (STR-CO) of the right calf in all trials. CBR function was assessed using rapid pulses of neck pressure from +40 to -80mmHg. In all IC trials, stretch did not alter maximal gain of carotid-cardiac (CBR-HR) and carotid-vasomotor (CBR-MAP) baroreflex function curves. The CBR-HR curve was reset without change in maximal gain during STR-CO in the IEL trial. However, during the IER trial maximal gain of the CBR-HR curve was smaller compared to all other trials (-0.34±0.04 in IER v -0.76±0.20, -0.94±0.14 and -0.66±0.18 b.min-1.mmHg-1 in ICR, IEL and ICL, respectively), and significantly smaller than in IEL (P<0.05). CBR-MAP curves were reset from CO values by STR-CO in the IEL and IER trials with no changes in maximal gain. These results suggest that metabolite sensitisation of stretch-sensitive muscle mechanoreceptive afferents modulates baroreflex control of heart rate but not blood pressure.

Key Words: Baroreceptor, Cardiovascular, Mechanoreceptor