Cardiac Autonomic Regulation under Hypnosis Assessed by Heart Rate Variability: Spectral Analysis and Fractal Complexity

Abstract

Objective: This study examined the effects of hypnosis on autonomic cardiac control. We hypothesized a modification of autonomic modulation of the heart rate with an enhanced vagal tone during hypnosis compared to baseline. Methods: In 12 healthy subjects (6 men and 6 women, 22.2 ± 1.0 years of age) ECG was recorded at baseline and during hypnosis. Heart rate variability parameters were obtained in the frequency domain (LFnu: low frequency normalized units, and HFnu: high frequency normalized units) and from nonlinear analysis methods (detrended fluctuation analysis, DFA). Results: Compared to the control condition, hypnosis showed a significantly decreased LFnu, a significantly increased HFnu, and a significantly decreased LF/HF. DFA showed a significantly decreased short-range similarity. Heart rate remained unchanged. Conclusion: Autonomic cardiac tone is significantly modified during hypnosis by shifting the balance of the sympathovagal interaction toward an enhanced parasympathetic modulation, accompanied by a reduction of the sympathetic tone and a decreased short-range similarity but without a concomitant change in heart rate. Central and secondary autonomous nervous system changes induced by hypnosis are a possible explanation for our results. Another highly probable explanation is given by a variation in the depth of respiration. Hypnosis appears to prevent the autonomic responses expected during neutral stimulation.