Effects of thiopentone, etomidate and propofol on beat-to-beat cardiovascular signals in man.

Analysis of beat-to-beat fluctuations of heart rate and blood pressure is a promising new approach to the clinical diagnosis and management of alterations in cardiovascular regulation. We investigated the effects of three induction agents on beat-to-beat heart rate and blood pressure fluctuations in man. Beat-to-beat fluctuations were analysed by spectral analysis. Two spectral areas are of main interest. One area is centred on the respiratory frequency and shifts with changes in respiratory rate (High Frequency area). These high frequency fluctuations in heart rate are caused by respiratory-induced blood pressure fluctuations, mediated by the vagus nerve through the baroreflex mechanism. Variability in the Low Frequency area, which occurs between 0.06 and 0.12 Hz is considered to be related to haemodynamic fluctuations due to the sympathetic baroreflex control loop of vasomotor activity and heart rate. Results from our study indicate that thiopentone, etomidate and propofol show considerable differences in their effects on beat-to-beat variability of heart rate and blood pressure. These differences can be explained by their specific effects on the cardiovascular system.