Evaluation of the heart rate variability using the HRV analysis during general anesthesia

We examined the spectral analysis and 1/f noise of heart rate variability during enflurane anesthesia in order to assess the effect of activity of the autonomic nervous system. Data were acquired from 15 patients (ASA I-II) who got the gynecological surgery under general anesthesia using enflurane, nitrous oxide and oxygen. We have analyzed the spectral components of HRV according to the following five periods: 1) before premedication (S_pre) 2) after induction (S_indu) 3) skin incision (S_inci) 4) recovery (S_awake) 5) after surgery (S_post). For each power spectrum density, the frequency components were identified as follows: (1) LF component (0.04-0.15 Hz) is associated with parasympathetic and sympathetic tone effected by body temperature, rennin-angiotensin system, baroreceptor and vasomotor sympathetic modulation, (2) HF component (0.15-0.5 Hz) mediated parasympathetic tone and reflecting mechanical influence of ventilation. In addition the LF/HF ratio reflecting the cardiac sympathovagal balance was monitored. The LF/HF ratio that reflects the balance of the autonomic nervous system increased remarkably during skin incision and recovery. Also, the index that shows the body activity decreased during skin incision and recovery. The increase of LF/HF was caused by mechanical stimulation, which reflects the autonomous nervous system balance. The index was useful for assessment of the body activity.