Monitoring of parasympathetic tone with ANI (Analgesia/Nociception Index) during hypnosis

A new index derived from heart rate variability called Analgesia/Nociception Index (ANI) reflecting the relative parasympathetic tone was recently developed to quantify the nociception/antinociception balance during general anesthesia. An ANI value close to 100 corresponds to prominent parasympathetic tone (low stress level, analgesia) and a value close to 0 corresponds to prominent sympathetic tone (high stress level, nociception). It has been previously described that hypnosis has an impact on the autonomous nervous system regulation by increasing the parasympathetic tone. We have performed two studies assessing ANI variations during hypnosis, in both volunteers and patients undergoing regional anesthesia procedures. The subject of this lecture is to describe the principles of calculation of ANI and to present the results of these studies so as to show an objective measurement of the parasympathetic tone during hypnosis sessions