Respiratory sinus arrhythmia is reversed during positive pressure ventilation.

In order to study the relationship between heart rate and depth of anaesthesia, respiratory sinus arrhythmia (RSA) was investigated during enflurane and isoflurane anaesthesia in 28 patients (15-39 years). Positive pressure ventilation (six breaths min-1) was used. Respiratory sinus arrhythmia was evaluated during light anaesthesia, deep anaesthesia (burst suppression in EEG) and light anaesthesia again by using signal averaging technique. In most patients, decrease of the heart rate was seen during inspiration (positive tracheal pressure), and increase during expiration. Respiratory sinus arrhythmia did not disappear in deep anaesthesia. Inter-individual variation in the magnitude and phase relationship of respiratory sinus arrhythmia was considerable, and was not associated to the level of anaesthesia.