Local and systemic vasodilation following hypnotic suggestion of warm tub bathing

During hypnosis it is easy to induce hallucinations having, for the hypnotized subject, the characteristics and the concreteness of reality. This study was performed to put in evidence the physical effects of hypnotic suggestion of warm tub bathing. 18 volunteers screened for high hypnotizability were studied. They underwent suggestion of forearm in warm water (30 min), suggestion of body in warm water (30 min), and hypnosis without any thermal suggestion (30 min), while blood pressure, heart rate, body temperature, forearm flow and resistance, stroke volume, cardiac index and total peripheral resistance were monitored. During suggestion of forearm in warm water, local vasodilation was recorded, with decrease of forearm resistance (-18%, P<0.01) and increase of forearm blood flow (+43%, P<0.01) like in real local passive warming. During suggestion of whole-body in a warm water tub, there was a systemic vasodilation with decrease of total peripheral resistance (-29%, P<0.01) and increase of cardiac index (+54%, P<0.01), like in real total-body passive warming. Body temperature, arterial blood pressure and heart rate were unchanged. During simple hypnosis (sham procedure) no haemodynamic variations were observed. These results are in keeping with the possibility to induce through hypnotic suggestion of heat a physical pattern that is typical of hyperthermia, even without increase in body temperature.