We performed spectral analysis and determined the 1/f noise of heart rate variability during enflurane anaesthesia in order to assess the effect of the activity of the autonomic nervous system.

Data were acquired from 15 patients (ASA I-II) who received gynecological surgery under general anesthesia using enflurane, nitrous oxide and oxygen. We analyzed the spectral components of heart rate variability (HRV) according to the following five periods: 1) before premedication, 2) after induction, 3) during skin incision, 4) during recovery, and 5) after surgery. For each power spectrum the density and frequency components were identified as follows: (1) low frequency (LF) component (0.04-0.15 Hz) was associated with parasympathetic and sympathetic tone, and was affected by body temperature, the renin-angiotensin system, baroreceptor and vasomotor sympathetic modulation, (2) high frequency (HF) component (0.15-0.5 Hz) was mediated parasympathetic tone and reflected the mechanical influence of the ventilation. In addition the LF/HF ratio, which reflected cardiac sympathovagal balance was monitored.

The LF/HF ratio, which reflects the balance of the autonomic nervous system increased remarkably during skin incision and recovery. Also, the β index, which is related to body activity decreased during skin incision and recovery.

Increased LF/HF was found to be caused by mechanical stimulation, which reflects autonomic nervous system balance, and the β index was useful for the assessment of body activity.