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1 Waseda University
2 National Cardiovascular Centre Research Institute
3 National Cardiovascular Center Research Institute
4 Kyushu University
5 National Cardiovascular Center
* To whom correspondence should be addressed. E-mail: kenta{at}aoni.waseda.jp.
Although the muscle mechanoreflex is one of the pressor reflexes during exercise, its interaction with dynamic characteristics of the arterial baroreflex remains to be quantitatively analyzed. In anesthetized, vagotomized, and aortic-denervated rabbits (n = 7), we randomly perturbed isolated carotid sinus pressure (CSP) by using binary white noise while recording renal sympathetic nerve activity (SNA) and arterial pressure (AP). We estimated the transfer functions of the baroreflex neural arc (CSP to SNA) and peripheral arc (SNA to AP) under conditions of control and muscle stretch of the hindlimb (5 kg of tension). The muscle stretch increased the dynamic gain of the neural arc while maintaining the derivative characteristics (gain at 0.01 Hz: 1.0 ± 0.2 vs. 1.4 ± 0.6 au mmHg-1; gain at 1 Hz: 1.7 ± 0.6 vs. 2.7 ± 1.4 au mmHg-1; control vs. stretch; P < 0.05). In contrast, muscle stretch did not affect the peripheral arc. In the time domain, muscle stretch augmented the steady-state response at 50 s (-1.1 ± 0.3 vs. -1.7 ± 0.7 au; control vs. stretch; P < 0.05) and the negative peak response (-2.1 ± 0.5 vs. -3.1 ± 1.5 au; control vs. stretch; P < 0.05) in the SNA step response. A simulation study using the experimental results indicates that the muscle mechanoreflex would accelerate the closed-loop AP regulation via the arterial baroreflex.
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