Power spectral analysis of heart rate and blood pressure variability in lumbar epidural anaesthesia

Abstract

The purpose of this study was to evaluate autonomic nervous system activity during high and low lumbar epidural anaesthesia. Ten patients undergoing lower limb surgery with lumbar epidural anaesthesia (low epidural anaesthesia group; mean upper dermal block level, T10.7± 1.1), and ten patients undergoing either abdominal total hysterectomy or ingunial hernia under lumbar epidural anaestehsia (high epidural anaesthesia group; mean upper dermal block level, T5.1± 1.0). Ten healthy volunteers were used as the control group. The autonomic nervous system activity was measured by heart rate and blood pressure variability with power spectral analysis. For the analysis of heart rate variability, frequency components were divided into two factors, a low frequency component RR (LFC rr: 0.03 Hz-0.15 Hz) that mediated sympathetic and parasympathetic activity and a high frequency component RR (HFC RR: 0.15 Hz-0.4 Hz) that mediated parasympathetic activity. In the analysis of blood pressure variability, the frequency components were also divided into two factors; a low frequency component of systolic blood pressure and diastolic blood pressure (LFC sbp and LFC dbp: 0.03 Hz-0.15 Hz) that was mediated by peripheral sympathetic vasomotor activity and a higher frequency component of systolic blood pressure and diastolic blood pressure (HFC SBP and HFC dbp: 0.15 Hz-0.4 Hz) that was mediated by a mechanical consequence of respiration. There were no changes in heart rate variability during epidural anaesthesia. However, LFC sbp and LFC dbp decreased in high epidural anaesthesia (P < 0.01). On the contrary, LFC sbp increased in low epidural anaesthesia (P < 0.01). We conclude that peripheral sympathetic vasomotor activity was activated in low epidural anaesthesia and suppressed in high epidural anaesthesia. © 1994 Canadian Anesthesiologists.