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

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 inguinal hernia under lumbar epidural anaesthesia (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 (LFCRR: 0.03 Hz-0.15 Hz) that mediated sympathetic and parasympathetic activity and a high frequency component RR (HFCRR: 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 (LFCSBP and LFCDBP: 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 (HFCSBP and HFCDBP: 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, LFCSBP and LFCDBP decreased in high epidural anaesthesia (P < 0.01). On the contrary, LFCSBP increased in low epidural anaesthesia (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)