TIME-FREQUENCY SPECTRAL-ANALYSIS OF HEART-RATE-VARIABILITY DURING INDUCTION OF GENERAL-ANESTHESIA

We have examined the spectral components of heart rate variability (HR V) during induction of anaesthesia with thiopentone, tracheal intubati on and subsequent inhalation of isoflurane-nitrous oxide. Commonly use d spectral analysis methods such as fast Fourier transformation or aut oregressive modelling require stationary data and are not suitable for the rapidly changing HRV data in this period. An advanced spectral an alysis method, time-frequency analysis, which can treat non-stationary data, was used in this study. Multiple spectra were generated to demo nstrate the time-related spectral components of HRV. Mid-frequency pow er (MF, 0.08-0.15 Hz), high-frequency power (HF, 0.15-0.5 Hz) and MF/H F ratio at baseline, after induction (before intubation), immediately after intubation and during maintenance periods were calculated and co mpared. MF and HF powers decreased after induction and were reduced fu rther in the maintenance period but MF/HF ratio remained unchanged aft er induction. Immediately after intubation MF and HF powers did not di ffer significantly from the immediate pre-intubation values, but MF/HF ratio did.