Background. The autonomous nervous system (ANS) is a key substrate for the regulation of gastrointestinal homeostasis and plays a substantial role in the pathophysiology of IBS. A convincing amount of evidence indicates a relationship between specific patterns of disturbed sympathovagal balance, symptom severity, and IBS subtypes. According to the literature, hypnosis affects sympathovagal balance by inducing elevated parasympathetic nervous system activity and reduced sympathetic tone. Previous studies reported clinical improvements of IBS-symptoms after successful Gut-directed group Hypnotherapy (GHT) over long-term periods but rarely depicted the underlying alterations in ANS regulation.

Aims of the study. The aim of this study is to investigate short- and long-term effects of Gut- directed group Hypnotherapy (GHT) on ANS regulation in refractory IBS-subjects, measured by heart rate variability. We further attempt to reveal differences in effects of GHT treatment on ANS regulation between IBS-subtypes (constipation-predominant vs. diarrheapredominant) and examine the relationship between self-rated hypnotic depth and parasympathetic activity. Methods. Within a period of 29 months, a sample of N=50 consecutive IBS-patients receive GHT treatment (7-10 weekly sessions) at the Psychosomatic Out-patient Clinic, Division of Gastroenterology and Hepatology, University Hospital of Vienna. Alterations in heart rate variability (HRV) are extracted by Electrocardiogram (ECG) recording in supine (30 min), sitting (10 min) and standing (10 min) position. HRV indices of sympathetic and parasympathetic control are quantified by using measures from time and frequency domains. Assessment of psychological variables is carried out by standardized questionnaires: anxiety, depression, stress, resilience, quality of life and IBS symptom burden.

Methods. Recordings of heart rate and R-R intervals will be conducted continuously for 24 hours. Electrocardiogram (ECG) recordings will be performed within one week before the first and after the last session of hypnosis. Patients will previously informed about the practical requirements for the recordings as well as the role of heart rate variability for health and the presumed associations between Autonomous Nervous System function, psychological stress reactivity patterns and digestive function. Recording devices will be mounted and activated at the hospital. Patients will return to their home or work environment and will be instructed not to ingest stimulating drinks (such as coffee, energy drinks), alcohol and not to engage in physical exercises during the whole recording time. Patients will return to the hospital \>24h later for removal and readout of the recording devices. Recorded data will be transferred to Kubios HRV® analysis software (version 2.2, Kuopio, Finland) for subsequent analysis. Calculated parameters comprise mean heart rate, square root of the mean squared differences of successive RR intervals (RMSSD), standard deviation of the normal-to-normal interval (SDNN) in the time domain, and and the number of pairs of succession normal-to-normal intervals that differ by more than 50ms divided by the total number of normal-to-normal intervals (pNN50); in the frequency domain low frequency (0.04-0.15 Hz, LF) and high frequency (0.16-0.40 Hz, HF) will be considered as proposed by international guidelines.