Power spectral analysis of heart rate variability during positive pressure pneumoperitoneum: The significance of increased cardiac sympathetic expression

Background: Positive pressure pneumoperitoneum (PPP) effects on the autonomic nervous system (ANS) might be of clinical importance, as imbalance in the autonomic cardiac control might lead to serious consequences. Methods: Fifteen healthy patients undergoing elective laparoscopic cholecystectomy were analyzed for cardiac autonomic nervous activity by spectral heart rate variability, during awake state, before and after intubation, during CO₂ PPP (14 mmHg), and after CO₂ evacuation. The very low, low, high and very high frequency (VLF, LF, HF, VHF respectively) bands of the spectral density of the heart rate variability (HRV) and their normalized values, as well as the LF/HF ratio, were obtained from the power spectra of R-R intervals, using the fast-Fourier transformation algorithm. Results: Using Friedman's nonparametric test, only the difference between the power of LF during anesthesia (median 30.74) and the middle of PPP (median 195.66) was found to be significant (p < 0.012). Such change was recorded in 14 patients (p = 0.001, sign test). Conclusions: Increased LF power reflects sympathetic cardiac activation. As the LF range accounts for regulation of blood pressure and baroreflex, several mechanisms may explain this activation. This in turn may predispose patients who suffer from cardiac disease to higher risk of developing ventricular arrhythmias, besides the possible adverse hemodynamic consequences of PPP.