• D P Landry, F M Bennett, and N E Oriol.
• Department of Anesthesia and Critical Care, Beth Israel Hospital, Harvard Medical School, Boston, Massachusetts 02215.
• Reg Anesth. 1994 May 1; 19 (3): 189-95.

Background And ObjectivesThe purpose of this study is to determine if spectral analysis of beat-to-beat heart rate variability will provide important data on autonomic nervous system function during either spinal or epidural anesthesia that is not apparent from the monitoring of mean heart rate and blood pressure.MethodsTwelve ASA I patients presenting for elective cesarean delivery (7 epidural and 5 spinal anesthetics) were prospectively selected for study. Control and postblock 10-minute segments of instantaneous heart rates were analyzed for each patient. The total spectral power (Ps, 0.02-0.5 Hz), low frequency spectral power (PLF, 0.02-0.12 Hz), and high frequency spectral power (PHF, 0.12-0.5 Hz) were calculated for each data segment. The complexity of the heart rate time series was estimated by calculating the approximate entropy.ResultsNeither spinal or epidural anesthesia had any effect on heart rate or blood pressure. Both spinal and epidural anesthesia did produce a significant decrease in PS, PLF, and PHF. Although there were significant decreases in both the PLF and PHF, there was no change in the PLF/PHF ratio. There was a significant reduction in approximate entropy with spinal and epidural anesthesia, indicating a decrease in complexity of the heart rate dynamics.ConclusionsThese data suggest that autonomic tone decreased with spinal and epidural anesthesia but the sympathetic-parasympathetic balance (expressed as PLF/PHF) did not change. Spectral measures, as well as approximate entropy, provide an independent evaluation of the integrity of the autonomic nervous system and cardiovascular control mechanisms that cannot be discerned from mean heart rate and blood pressure.

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