Response to Letter to Editor – Comments on: Sympathetic vasomotor outflow during low‐intensity leg cycling in healthy older males

Abstract

We wish to express our appreciation for Drs Notarius and Floras's insightful comments concerning our recent published study on sympathetic vasomotor outflow during low-intensity leg cycling in older males (72 ± 3 years of age, mean ± SD; Katayama et al., 2022).We would like to take this opportunity to respond regarding our work, because our experimental procedure was based, in part, on their previous study (Notarius et al., 2019).One of the major comments concerns the possible mechanism for the decreased muscle sympathetic nerve activity (MSNA) during leg cycling in our study. Drs Notarius and Floras have suggested that the decrease in MSNA during leg cycling in older males is mediated, in part, by the arterial baroreflex, owing to a greater increase in arterial blood pressure (ABP), secondary to attenuated conduit artery compliance.There is no doubt that the arterial baroreflex contributes to the regulation of sympathetic vasomotor outflow during exercise, and thus, we agree, in part, with their concerns. However, it is well established that the arterial baroreflex resets during dynamic exercise, indicating that the operating point of the arterial baroreflex (resting blood pressure) becomes the exercise-induced high value of ABP (Raven et al., 2006). Moreover, the moving operating point of ABP in the arterial baroreflex occurs very quickly (Barbosa et al., 2016;DiCarlo & Bishop, 1992;Fisher et al., 2007), and thus the arterial baroreflex does not respond to the exercise-induced increase in ABP (Raven et al., 2006). Considering this background, the effect of arterial baroreflex control of sympathetic vasomotor outflow during exercise might be minor. Although it has been reported that the cardiopulmonary baroreflex also resets during dynamic exercise (Ogoh et al., 2006), we have shown that the cardiopulmonary baroreflex plays an important role in regulating MSNA outflow at the onset of exercise (Ogoh et al., 2022). Thus, the resetting of the cardiopulmonary baroreflex might not be as rapid as the arterial baroreflex.In our previous study (Katayama et al., 2014), we measured MSNA in young males performing leg cycling at different pedalling frequencies to alter the muscle pump and central blood volume. This design allowed us to examine whether cardiopulmonary loading modulates sympathetic vasomotor outflow during cycling in young males. Consequently, a significant decrease in MSNA was observed duringThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.