Influence of age on respiratory modulation of muscle sympathetic nerve activity, blood pressure and baroreflex function in humans

Healthy ageing and alterations in respiratory-sympathetic coupling have been independently linked with heightened sympathetic neural vasoconstrictor activity. We investigated how age influences the respiratory related modulation of muscle sympathetic nerve activity (MSNA), and the association between the rhythmic fluctuations in MSNA and blood pressure that occur with respiration (Traube-Hering Waves; THW). Ten young (22 ± 2 years, mean±SD) and ten older (58 ± 6 years) healthy men were studied while resting supine and breathing spontaneously. MSNA, blood pressure and respiration were simultaneously recorded. Resting values were ascertained and respiratory cycle triggered averaging of MSNA and blood pressure measurements performed. MSNA burst incidence was higher in older individuals (22.7 ± 9.2 vs. 42.2 ± 13.7 bursts·100 heartbeats(-1) P<0.05), and was similarly reduced in the inspiratory to post-inspiratory period in young and older subjects (by ∼25% compared to mid-to-late expiration). A similar attenuation of MSNA burst frequency (bursts per minute), amplitude and total activity (burst frequency × mean burst amplitude) was also observed in the inspiratory to post-inspiratory period in both groups. A significant positive correlation between respiratory related MSNA and THW magnitude was observed in all young (100%) and most older (80%) subjects. These data suggest that the strength of the cyclical inhibition of MSNA during respiration is similar between young and older individuals and thus alterations in respiratory-sympathetic coupling appear not to contribute to the age-related elevation in MSNA. Furthermore, central respiratory-sympathetic coupling plays a role in the generation of THW in both healthy young and older humans. This article is protected by copyright. All rights reserved.