[The autonomic nervous activities in man under thoracic epidural anesthesia assessed by heart rate fluctuation...

The R-R intervals of an electrocardiogram, the coefficient variation of R-R intervals (CV-RR), and the power spectrum of heart rate fluctuation were studied just before surgical operations in a group of 10 patients who underwent high thoracic epidural anesthesia (TEA), and before anesthesia in a control group of 10 patients who were scheduled for general anesthesia without TEA. When TEA was performed, the CV-RR increased significantly (P less than 0.05). An increasing tendency (P less than 0.1) was also observed in the R-R intervals and the spectral analysis of the peak amplitude of the low frequency component (LFC) of 0.05 to 0.15 Hz. This tendency was found, too, in the band areas of the LFC and the high frequency component (HFC) of 0.15 to 0.4 Hz. These data indicate that the sympathetic innervation of the heart might have been interrupted by TEA and the vagal tone might have become dominant. Subsequent intravenous administration of atropine 0.5 mg reduced the R-R intervals, the CV-RR, the peak amplitude and the band areas of the LFC and HFC (P less than 0.01), as were seen in the control group. These evidences will show that the heart rate regulation of man in a supine position is dominantly influenced by the vagal tone, and it will become more prominent under TEA by blocking the cardiac sympathetic innervation at spinal level. Present study also suggests that a contribution of the cardiac sympathetic nerve on heart rate fluctuation, even on LFC, is only slight.(ABSTRACT TRUNCATED AT 250 WORDS)