Autonomic profile under hypnosis as assessed by heart rate variability and spectral analysis

To test the hypothesis of a sympathovagal balance shift towards an enhanced vagal tone under the condition of a standardized hypnosis, we used the assessment of heart rate variability including spectral analysis in 10 healthy subjects (5 female, 5 male, age ranging from 27 to 42 years). We compared the subjects under baseline condition (resting) and under hypnosis, measured on a different day, for a measuring period of five minutes for each condition. The result was reduced total power in the low frequency band (0.01-0.05 Hz) reflecting sympathetic activity. Also, the ratio of low to high frequency power (LFIHF) was reduced when under hypnosis. This reduction was due to a reduced LF component, but only a slightly reduced mid frequency component. With considerable variability, we also found activated mid frequency bands (0.05-0.15Hz) under hypnosis, likely reflecting baroreceptor activity. We conclude that the autonomic status in hypnosis is associated with a change towards reduced low frequency activity, but not necessarily with enhanced high frequency activity.