Cardiovascular indices of peripheral and central sympathetic activation

Objective: A number of sympathetic nervous system (SNS) parameters have bee n used in cardiovascular psychophysiology. This study aimed to describe the pattern and redundancy of a set of SNS parameters during peripherally indu ced changes of cardiac sympathetic activation and reflex modulation of cent ral SNS control. Preejection period (PEP) was assessed as a marker of perip heral sympathetic activation. Low-frequency blood pressure variability (BPV ) was assessed as an estimate of central SNS control. Methods: Peripheral b eta -sympathetic stimulation and blockade were achieved with epinephrine an d esmolol hydrochloride (beta (1)-blockade), respectively. Changes in centr al SNS output were induced by loading and unloading arterial baroreceptors with norepinephrine and nitroprusside sodium, respectively. This single-bli nded, crossover study in 24 healthy men also included two placebo control p eriods. PEP was derived from impedance cardiography and adjusted individual ly for heart rate. BPV was calculated by power spectral analyses of beat-to -beat heart rate and systolic blood pressure (Finapres system) data. Result s: PEP decreased during epinephrine infusion (-40.1 +/- 3.8 ms, p < .0001) and increased during esmolol infusion (+6.6 +/- 3.5 ms, p = .05). PEP was s hortened after central SNS activation by nitroprusside (-16.8 +/- 2.9 ms, p < 0.0001). Systolic BPV in the low-frequency range (0.07-0.14 Hz, Mayer wa ves) increased during nitroprusside infusion (+0.44 +/- 0.19 In mm Hg-2, p = .03) and decreased during norepinephrine infusion (-0.67 +/- 0.13 In mm H g-2, p < 0.0001). Low-frequency BPV did not change significantly during epi nephrine or esmolol infusion. Conclusions: Our data provide empirical evide nce of separable peripheral and central sympathetic response components. Th e combined report of low-frequency BPV and PEP gives distinct information o n both central SNS control and the level of sympathetic cardiac activation achieved.