BACKGROUND: Although heart rate variability (HRV) and blood pressure variability (BPV) arise from many different influences, probably the most consistent external modulator is respiration. At rest, the heart rate increases on inspiration and decreases on expiration, a phenomenon called respiratory sinus arrhythmia (RSA). Spectral analysis of heart rate offers good and reproducible estimate of RSA and BPV. Many studies have been conducted on the effects of respiration on HRV and BPV during awake subject breathing spontaneously. However, little is known as to whether respiratory rate modulates HRV and BPV during general anesthesia with mechanical ventilation. Here, we studied effects of respiratory rate on HRV and BPV during general anesthesia.

METHODS: We studied 40 patients undergoing general anesthesia with mechanical ventilation. Maintaining anesthesia with isoflurane, we recorded R-R interval and systolic blood pressure at respiratory rate of 15, 10 and 6 breaths/minute. Data was analyzed by the power spectral analyses of HRV and BPV, which were divided into low frequency (LF) and high frequency (HF) band.

RESULTS: Respiratory rate did not affect RR interval, systolic blood pressure, and total spectral power HRV and BPV. Compared with its value at 15 breaths/minute, HF-HRV was significantly increased at 6 breaths/minute. HF-and LF-BPV at 6 breaths/minute were significantly increased versus 15 breaths/minute.

CONCLUSIONS: Respiratory rate modulates HRV and BPV during general anesthesia with mechanical ventilation. We suggest that respiratory rate should be considered and controlled in studies of cardiovascular variability during general anesthesia.