Aging Effects of Sympathetic Reflex Activities on Skin Nerves

Background: Muscle sympathetic nerve activity (MSNA) at rest is widely known to increase with aging, but changes in skin sympathetic nerve activity (SSNA) with aging are less well defined. We examined the aging effects of reflex activities on SSNA, sympathetic skin response (SSR), and sympathetic flow response (SFR). Objective: We studied the aging effect of reflex activities on SSNA, SSR and SFR. Methods: SSNA, SSR and SFR were simultaneously recorded during randomly administered electrical stimuli. Results: The mean SSNA reflex latency was 763.1 ± 39.8 ms, mean SSNA amplitude was 12.6 ± 6.3 µV, mean SSR reflex latency was 1,809.0 ± 90.6 ms, mean SSR reflex amplitude was 0.519 ± 0.449 mV, mean SFR reflex latency was 4,398.9 ± 761.7 ms, and mean SFR reflex amplitude was 8.21 ± 5.14 ml/min/100 g. None of these parameters were significantly affected by aging. The reflex bursts on SSNA could be recorded in all subjects studied. While the frequencies of SSR and SFR were recorded in more than 80% of young subjects under age 40 years, the frequencies of SSR were recorded in less than 25% of subjects over age 80 years, and the frequencies of SFR were recorded in less than 5%. Conclusion: There were no differences in electrical stimuli-induced reflex SSNA between young and older subjects, but effector organ responses such as SSR and SFR were diminished in older subjects.