Effects of surgical stimulation on autonomic reflex function: assessment by changes in heart rate variability

Analysis of small oscillations in heart rate (known as heart rate variability or HRV) associated with the activity of homeostatic reflexes can provide a noninvasive measure of autonomic reflex function. We have investigated the effects of surgical stimulation on autonomic reflex function by assessment of changes in HRV. Healthy female patients undergoing laparoscopic tubal ligation were anaesthetized with either thiopentone-nitrous oxide-isoflurane (group I; n = 13) or continuous propofol infusion (group P; n = 13). Power spectral measurements of HRV (HRVtot = total HRV power; %HRVlo = percent of HRV power in the low frequency range) were obtained at the following times; control; before incision; after incision (3 min, 10 min and before skin closure). Compared with control values, measurements of HRVtot before incision were reduced significantly in both groups (group P: 16 (SEM 3)% of control; group I: 2.5 (0.7)% of control). With surgical stimulation, mean HRVtot in group P was restored to 55 (13)% of control (P < 0.01 compared with measurement before incision), whereas mean HRVtot in group I remained at less than 4% of control (ns). %HRVlo increased also in group P, from 49 (7)% to 75(3)% (P < 0.05), consistent with a shift in sympathetic-parasympathetic balance towards sympathetic dominance. These results suggest that surgical stimulation may have significant effects on the autonomic reflexes mediating HRV, and that such effects vary with anesthetic technique.