The effects of cervical and lumbar epidural anesthesia on heart rate variability and spontaneous sequence baroreflex sensitivity.

A high level of neuroaxial block may produce profound bradycardia and hypotension, possibly as a result of an imbalance between sympathetic and parasympathetic control of heart rate. We designed this study to test the hypothesis that cervical epidural anesthesia would increase the high-frequency (HF) component of heart rate variability (HRV) as a result of cardiac sympathectomy, whereas lumbar epidural anesthesia would cause sympathetic predominance. HRV and spontaneous baroreflex (SBR) sensitivity were assessed before and after cervical and lumbar epidural anesthesia by using plain 1.5% lidocaine (median upper/lower sensory block: C3/T8 for cervical and T11/L5 for lumbar) in healthy patients (n = 10 each). Electrocardiogram and noninvasive beat-to-beat arterial blood pressure were monitored. HRV was analyzed by using fast Fourier transformation. Least-square regression analysis relating R-R interval and systolic blood pressure during spontaneous fluctuation was performed to obtain SBR sensitivities. Cervical epidural group patients were significantly older (P < 0.01) and taller (P < 0.01). Cervical epidural anesthesia attenuated HF (0.15-0.4 Hz) and low-frequency (0.04-0.15 Hz) power of HRV with concomitant reductions in up- and down-sequence SBR sensitivities, suggesting decreased vagal modulation of heart rate. Lumbar epidural anesthesia resulted in a significant increase in the low-frequency/HF ratio of HRV and unchanged SBR indices, suggesting sympathetic predominance. HF power correlated well with SBR sensitivities under most of our study conditions. Respiratory rates and Paco(2) were unchanged by either epidural technique. Our results indicate that cervical, but not lumbar, epidural anesthesia depresses phasic and tonic dynamic modulation of the cardiac cycle by the vagal nerve in conscious humans.