BRS during passive exercise

During exercise central command and the exercise pressor reflex reset the arterial baroreflex (Raven et al. 2005). While the role of the metabolic component of the exercise pressor reflex in this resetting has been investigated (Iellamo et al. 1997; Papelier et al. 1997) the discrete contribution of mechanoreceptors is not clear. The aim of the present study was to determine the contribution of mechanoreceptors on the integrated arterial baroreflex control of the sinus node during dynamic exercise. Passive exercise, where only muscle mechanoreceptor afferents are likely to be stimulated, was accomplished by using a tandem bicycle with a second rider performing the movements. Systolic arterial pressure (SAP) and heart rate (HR) were measured continuously and noninvasively in eight subjects (age, mean ± S.E.M., 28.1 ± 2.1 years) pre and during a 5 min bout of passive cycling at 60 revolutions per minute. Surface electromyography (EMG) of the vastii muscles ensured absence of volitional contraction. Spontaneous baroreflex sensitivity (BRS) was evaluated as the slope of sequences of three or more consecutive beats in which systolic blood pressure and the R‐R interval either increased or decreased, in a linear fashion. SAP and HR increased from 126.9 ± 10.1 mmHg and 62.1 ± 7.6 bpm at rest to 136.8 ± 11.1 mmHg and 69.5 ± 4.3 bpm (P < 0.005) during passive exercise, respectively. BRS increased from 10.65 ± 2.4 ms mmHg −1 at rest to 16.81 ± 5.51 ms mmHg −1 (P < 0.001) during passive exercise. Also, there was a rightward and downward shift of the regression line relating SBR with the R‐R interval. These data suggest that activation of muscle mechanoreceptors contributes to the resetting of the arterial baroreflex during dynamic exercise.