Age-related changes in baroreflex control of heart rate and sympathetic nerve activity in healthy humans.

To determine how the baroreflex control of sympathetic nerve activity is affected by aging, muscle sympathetic nerve activity (MSNA) from the tibial nerve was monitored using microneurography, and heart rate and blood pressure were recorded during the pressor or depressor responses to intravenous injections of phenylephrine or nitroglycerin in 39 healthy humans, aged 16 to 56 years. Although the baroreflex slope for heart rate showed attenuation with aging, the baroreflex slope for MSNA was not affected by aging. These data suggest preservation of the baroreflex control of sympathetic nerve activity despite attenuation of the baroreflex control of parasympathetic nerve activity by aging in humans.