Autonomic changes during hypnosis: a heart rate variability power spectrum analysis as a marker of sympatho-vagal balance.

Spectral analysis of beat-to-beat variability in electrocardiography is a simple, noninvasive method to analyze sympatho-vagal interaction. The electrocardiogram is analyzed by means of an automatic, autoregressive modeling algorithm that provides a quantitative estimate of R-R interval variability by the computation of power spectral density. Two major peaks are recognizable in this specter: a low-frequency peak (LF, -0.1 Hz), related to the overall autonomic activity (ortho+parasympathetic) and a high-frequency peak (HF, -0.25 Hz), representative of the vagal activity. The LF/HF ratio is an index of the sympatho-vagal interaction. This technique was applied, using a computer-assisted electrocardiograph, to 10 healthy volunteers (6 high and 4 low hypnotizable subjects as determined by the Stanford Hypnotic Susceptibility Scale, Form C) in randomized awake and neutral hypnosis conditions. Preliminary results indicated that hypnosis affects heart rate variability, shifting the balance of the sympatho-vagal interaction toward an enhanced parasympathetic activity, concomitant with a reduction of the sympathetic tone. A positive correlation between hypnotic susceptibility and autonomic responsiveness during hypnosis was also found, with high hypnotizable subjects showing a trend toward a greater increase of vagal efferent activity than did low hypnotizables.

Effects of hypnotic analgesia and hypnotizability on experimental ischemic pain.

Mechanisms of hypnotic analgesia are still poorly understood and conflicting data are reported regarding the underlying neurochemical correlates. The present study was designed to investigate the effects of hypnotically induced analgesia and hypnotizability on experimental ischemic pain, taking into account pain and distress tolerance as well as the neurochemical correlates. 11 high hypnotizable Ss and 10 low hypnotizable Ss, as determined by scores on the Stanford Hypnotic Susceptibility Scale, Form C (Weitzenhoffer & E. R. Hilgard, 1962), were administered an ischemic pain test in both waking and hypnotic conditions. The following variables were measured: (a) pain and distress tolerance, (b) anxiety levels, and (c) plasma concentrations of beta-endorphin and adrenocorticotropic hormone (ACTH). Results confirmed significant increases of pain and distress tolerance during hypnosis as compared to the waking state, with positive correlations between pain and distress relief and hypnotizability. Moreover, a hypnotically induced dissociation between the sensory-discriminative and the affective-motivational dimensions of pain experience was found, but only in high hypnotizable Ss. Hypnotic analgesia was unrelated to anxiety reduction and was not mediated either by endorphins or by ACTH.