Autonomic status changes in coronary bypass surgery evaluated by heart rate and blood pressure variability

Heart rate (HRV) and blood pressure (BPV) variability were investigated in 25 patients undergoing CABG surgery. At four stages, 5-minutes of on-line data were used to calculate spectral power in high (0.15 to 0.4 Hz), low (0.04 to 0.15 Hz), and very low (0.003 to 0.04 Hz) frequency bands: 1) before anesthesia, 2) before skin incision, 3) at the end of surgery, and 4) the day after surgery. HRV and BPV are decreased by anesthesia and mechanical ventilation with predominance of vagal HF power as has been described. At the end of surgery, HRV is further decreased (with higher mean HR), while BPV rises, with high HF probably due to hypovolemia and nitrate therapy. On the morning after surgery, HRV is increased with reduced HF, while BPV exceeds control values in VLF and HF, showing sympathetic activation and still impaired blood pressure control.