GUT PAIN REACTIONS IN MAN - AN EXPERIMENTAL INVESTIGATION USING SHORTAND LONG-DURATION TRANSMUCOSAL ELECTRICAL-STIMULATION

Visceral pain is a substantial, clinical problem but unfortunately few experimental models are available to study this phenomenon in man. In the present study we inserted a stimulation catheter 5-10 cm into the ileo-sigmoidostomy of nine patients. The catheter contained six small , flexible electrodes separated by 4 mm. The gut was stimulated by sin gle burst, repeated burst (five stimuli delivered at 2 Hz), or continu ous burst stimuli (4 Hz for 30, 60, 90, and 120 s). The sensation (ST) , pain detection (PDT), and pain tolerance (PTT) thresholds to single/ repeated burst stimuli were determined. The location/size/sensitivity of referred pain after repeated/continuous stimulation were characteri zed. The brain potentials to single burst stimuli and to increasing st imulus intensity were measured. ST to single burst stimuli was easy to determine (8 mA) and to reproduce. The patients found it difficult to determine the PDT and PTT to single burst stimuli, however both thres holds were easily determined for repeated burst stimuli. The pain thre sholds to single burst stimuli were twice as high as the thresholds to repeated burst stimuli, indicating the importance of central temporal summation for visceral pain. Minor changes in the stimulus location r esulted in changes of the referred pain projection site. The words mos t frequently selected (78%) from the McGill Pain Questionnaire to desc ribe repeated burst stimulations were shooting, pricking, flashing, an d boring. The amplitude of the brain potentials increased at increasin g stimulus intensity. A stimulus intensity giving an initial pain rati ng of around 5 on a 0-10 visual analog scale (VAS) was used for contin uous stimulation. A general increase of the pain intensity and the are a of referred pain was found during this stimulation. It was concluded that electrical stimulation of the human gut provokes pain and especi ally long sequences of visceral stimuli are adequate to evoke referred pain mimicking pain profiles of pathologic origin.