Experimental pain in the stomach: a model based on electrical stimulation guided by gastroscopy

Abstract

Background-Abdominal pain is often variable in intensity and diYcult to characterise due to its referred pain pattern. Clinical pain is furthermore confounded by various emotional and cognitive factors. Aims-To develop and apply an experimental model to induce localised gastric pain. Subjects-Twelve healthy male volunteers. Methods-Stimulating electrodes were mounted on a biopsy forceps and electric stimuli were delivered during gastroscopy. Single, five repeated, and continuous stimuli were given at four locations in the stomach. Pain detection thresholds and pain intensities were assessed together with localisation of the referred pain area. Results-Pain detection thresholds were higher in the prepyloric region compared with those obtained at the lesser and greater curvature. Increasing stimulus intensity resulted in augmented pain perception and repeated stimuli elicited pain at a lower stimulus intensity than single stimuli. Continuous stimuli evoked constant (33%), increasing (33%), or decreasing (33%) pain. The localisation of referred pain varied considerably in the subjects. Conclusions-The model seems relevant to study basic pain mechanisms elicited by localised stimuli in the stomach. The experimental data support the premise that a gastric focus should always be suspected in patients referred with diVerent kinds of abdominal pain. (Gut 1997; 41: 753-757)

Multimodal assessment of pain in the esophagus: a new experimental model

“…Thus (in the subjects in whom the probe was in the correct position) no arrhythmias were observed, in contrast to previous studies, in which atrial capture was reported (9). Compared with our model using an endoscope (8,9,11), the current method did not allow visual inspection of the mucosa. On the other hand, the unpleasantness associated with the much thicker endoscope was avoided.…”

“…The electrical field will invariably activate receptors at mucosa, submucosa, and muscle layers depending on the intensity and thus represent a broad activation of the gut wall. The welldefined stimulation area and unique possibility for control of the time sequence give these stimuli several advantages (8,9). Hence, we showed an increased response to stepwise increments together with demonstration of temporal summation to repeated electrical stimuli.…”

“…Accordingly, when the subject reported that the stimuli resulted in pain and/or severe discomfort (Ͼ5 on the nonpainful scale) they were asked to score the intensity from 5-10 on the VAS. The VAS has previously been demonstrated to be useful to assess painful stimuli to electrical current and distension in the stomach and small and large intestine (2,8,11). After the experiment, the MPQ was used to assess the painful sensations qualitatively.…”

“…We used a protocol with pseudorandom sequences including lower-intensity stimuli interspersed with the ascending stimulus intensities. Such series have proven to be valuable in our previous studies using both electrical and mechanical stimuli (8,11,25). Thus intermittent sham stimuli with either no current or the same current as in the previous step were given to ensure that the subject did not automatically increase the sensory rating.…”

Multivariate Analysis of Single-Sweep Evoked Brain Potentials for Pharmaco-Electroencephalography

“…The electrodes were placed 35 cm distal from the incisors during the recordings and had the impedance adjusted to below 2 kOhm. Stimuli were applied every 5 s and consisted of five 1-ms 2 pulses at 200 Hz, which was felt as 1 short pulse in the oesophagus [21]. This visceral stimulus was chosen to mimic deep pain as reported most frequently in the clinic.…”