Purpose: The relationship between autonomic nervous system (ANS) activity a
nd general anesthesia has been explored. Studies have demonstrated partial
recovery of heart rate variability (HRV), representative of ANS activity, i
n the postoperative period, but the arousal period has not been precisely s
tudied. The goals of this study were to analyze modifications of ANS activi
ty during general anesthesia and, more particularly, around the arousal per
iod, to look for predictors of arousal.
Methods: We analyzed HRV changes using wavelet transform, a time-frequency
analysis that, in contrast to Fourier transform, is able to assess abrupt c
hanges of ANS activity. Seventeen patients (mean +/- SD age: 40.9 +/- 16.4
yr) under general anesthesia for hip or knee surgery, were included in the
study. The analysis began one hour before anesthesia, focussed on eye openi
ng, and ended three hours after arousal.
Results: There was a dramatic decrease in HRV after induction, that extende
d throughout anesthesia and represented a decrease in global autonomic regu
lation with, however, a relative predominance of vagal tone. At the moment
of eye opening, there was an abrupt change in HRV, representing a sudden sh
ift of ANS balance towards the predominance of sympathetic activity, while
none of these indices changed seconds before arousal.
Conclusions: Wavelet analysis of HRV appears to be powerful tool to precise
ly assess instantaneous changes of HRV during anesthesia. Using this method
, there were no identifiable precursory HRV indices of arousal.