AGING ALTERS THE RELATIVE CONTRIBUTIONS OF THE SYMPATHETIC AND PARASYMPATHETIC NERVOUS SYSTEMS TO BLOOD PRESSURE CONTROL IN WOMEN

摘要

Autonomic support of blood pressure (BP) increases with age in humans. Large differences exist in the dose of trimethaphan required for ganglionic blockade in young and older women. We asked if differences in the dose of trimethaphan required to achieve ganglionic blockade are due to differences in the relative contributions of the sympathetic and parasympathetic nervous systems in control of BP with age. Muscle sympathetic nerve activity (MSNA, microneurography, peroneal nerve), heart rate (HR), and blood pressure (BP) were recorded before and during incremental doses of trimethaphan camsylate until ganglionic blockade was achieved (absence of MSNA and <5bpm increase in heart rate during a valsalva maneuver; final trimethaphan dose: 1–7mg/min). Heart rate variability (HRV) was analyzed from the ECG waveform (WinCPRS). The dose of trimethaphan required to achieve ganglionic blockade is positively related to basal heart rate variability (HRV), where women with high HRV require a higher dose of trimethaphan to achieve ganglionic blockade. In contrast, baseline MSNA is inversely related with the dose of trimethaphan required to achieve ganglionic blockade, such that women with high basal MSNA required a lower dose of trimethaphan. As such, the change in HR with ganglionic blockade was positively related, and the change in MAP was inversely related, with the dose of trimethaphan required to achieve ganglionic blockade. These data suggest loss of parasympathetic tone and increased sympathetic tone with aging contribute to the increase in BP with age in women and dictate the dose of trimethaphan that is necessary to achieve ganglionic blockade.