Sympathetic vasomotor outflow during low‐intensity leg cycling in healthy older males

Abstract

Muscle sympathetic nerve activity (MSNA) is reduced during low-intensity dynamic leg exercise in young males. It is suggested that this inhibition is mediated by loading of the cardiopulmonary baroreceptors. The purpose of this study was to clarify the impact of age on MSNA during dynamic leg exercise. Nine younger males (YM, mean ± SD, 20 ± 1 years) and nine older males (OM, 72 ± 3 years) completed the study. The subjects performed two 4-min cycling exercises at 10% of their heart rate reserve using a cycle ergometer in a semirecumbent position (MSNA and estimated central venous pressure (eCVP) trials). MSNA was recorded via microneurography of the left radial nerve. The CVP was estimated based on peripheral venous pressure, which was monitored using a cannula in the right large antecubital vein. The magnitude of the increase in mean arterial blood pressure during leg cycling was larger in OM (+9.3 ± 5.5 mmHg) compared with YM (+2.8 ± 4.7 mmHg). MSNA burst frequency was decreased during cycling in both YM (-8.1 ± 3.8 bursts/min) and OM (-10.6 ± 3.3 bursts/min), but no significant difference was found between the two groups. The eCVP increased during exercise in both groups, and there was no difference in the changes in eCVP between YM (+1.1 ± 0.4 mmHg) and OM (+1.2 ± 0.7 mmHg). These data indicate that inhibition of sympathetic vasomotor outflow during low-intensity cycling appears in OM as seen in YM. It is possible that the muscle pump-induced loading of the cardiopulmonary baroreflex is preserved during cycling in healthy older males.

Influence of age on muscle sympathetic response to dynamic exercise

“…Importantly, our findings differ with respect to the influence of such exercise on heart rate, hence MSNA burst incidence. In contrast to Katayama et al (2022), heart rates of our older cohort rose less (P = 0.03), and their MSNA fell further (−19 ± 2 vs. −11 ± 2 bursts/100 heart beats; P = 0.01), indicating augmented reflex or centrally mediated sympathetic inhibition.…”

Cardiovascular reflex contributions to sympathetic inhibition during low intensity dynamic leg exercise in healthy middle‐age

“…However, when dynamic leg extension was performed supine, central venous pressure did not rise further and MSNA did not fall (Ray et al, 1993). In a recent report, central venous pressure during a similar mild dynamic leg exercise protocol did not differ between older and young healthy subjects (Katayama et al, 2022). Assuming similar engagement of the leg muscle pump at low-intensity exercise (Shiotani et al, 2002), the prior observation that inhibitory cardiopulmonary reflex modulation of MSNA is augmented with age (Davy et al, 1998) could account for the greater sympatho-inhibition during mild and moderate cycling we observed previously in healthy middle-aged compared with young subjects (Notarius, Millar, Doherty, et al, 2019).…”

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

“…As such, we also used a low workload (10% of heart rate reserve) in our study, but it appears that the magnitude of the decrease in MSNA with cycling was larger in our study than in the study by Notarius et al (2019). We speculate that two-legged cycling in our study (Katayama et al, 2022) induces a larger venous return (i.e., increase in eCVP) than one-legged cycling (Notarius et al, 2019), resulting in greater loading of cardiopulmonary baroreceptors during two-legged cycling. This might be the reason for the inconsistent MSNA data.…”

“…Other factors related to the sample characteristics might have led to inconsistencies between our studies. First, our subjects (Katayama et al, 2022) were older than the subjects in the study by Notarius et al…”

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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.

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