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

Visceral hyperalgesia/allodynia can be induced experimentally and assessed quantitatively by the newly introduced multi-modal psychophysical assessment approach. The significant changes of the experimentally evoked referred pain patterns and of the nociceptive reflex evoked from a distant somatic structure indicate that even short-lasting visceral hyperalgesia can generate generalised sensitisation.

Human experimental visceral pain models using chemical stimulation are needed for the study of visceral hyperexcitability. Our aim was to stimulate the human gut with chemical activators (capsaicin, glycerol) and measure quantitatively the induced hyperexcitability to painful mechanical gut distension. Ten otherwise healthy subjects with an ileostoma participated. Increasing volumes of capsaicin 50 microg/ml (0.25, 0.5, 0.75, 1.0, 1.5, 2.0, and 3 ml), glycerol (2.5, 5, and 10 ml) or saline (2.5, 5, and 10 ml) intermingled with sham stimuli were randomly applied to the ileum via the stomal opening at three occasions separated by a week. After each application, pain intensity, qualities, and referred pain area were assessed together with the pain threshold to distension of the proximal gut. 'Boring' and 'hot' pain were evoked in all subjects by low doses (median 0.5 ml) of capsaicin. The median pain onset, peak pain, and pain duration were 55, 85, and 420 s, respectively. Referred somatic pain developed around the stomal opening with a correlation between the pain area and pain intensity. After application of capsaicin, significant hyperalgesia was found to distension of the gut (a 28% reduction pressure in pain threshold). No significant manifestations were found after application of glycerol and saline. Application of capsaicin to the human ileum induces pain and mechanical hyperalgesia. Specific activation of nociceptors in the gut mucosa provides new possibilities to study clinical relevant visceral pain mechanisms.

gersen. Sensory and biomechanical responses to ramp-controlled distension of the human duodenum. Am J Physiol Gastrointest Liver Physiol 284: G461-G471, 2003. First published November 13, 2002 10.1152/ajpgi.00456.2001.-The aim of this study was to develop a new method for investigation of the relationship among the mechanical stimulus, the biomechanical properties, and the visceral perception evoked by volume/ramp-controlled distension in the human duodenum in vivo. An impedance planimetric probe for balloon distension was placed in the third part of the duodenum in seven healthy volunteers. Distension of the duodenum was done at infusion rates of 10, 25, and 50 ml/min. The pump was reversed when level 7 was reached on a visual analog scale ranging from 0 to 10. Distensions were done with and without the administration of the antimuscarinic drug butylscopolamine. The total circumferential tension (T total) and the passive circumferential tension (Tpassive) were determined from the distension tests without and with the administration of butylscopolamine, respectively. T total and Tpassive showed an exponential behavior as a function of strain (a measure of deformation). The active circumferential tension (T active) was computed as TtotalϪTpassive and showed a bellshaped behavior as a function of strain. At low distension intensities, the intensity of sensation at 10 ml/min was significantly higher than that obtained at 25 and 50 ml/min. The coefficient of variation at the pain threshold for circumferential strain (average 4.34) was closer to zero compared with those for volume (8.72), pressure (31.22), and circumferential tension (31.55). This suggests that the mechanoreceptors in the gastrointestinal wall depend primarily on circumferential strain. The stimulus-response functions provided evidence for the existence of low-and high-threshold mechanoreceptors in the human duodenum. Furthermore, the data suggest that high-threshold receptors are nonadapting.cross-sectional area; distensibility; duodenum; pain; lengthtension relationship VISCERAL PAIN IS ONE OF THE most frequent reasons patients seek medical attention. It is well known that distension of the gastrointestinal tract elicits reflexmediated inhibition and stimulation of motility via intrinsic or extrinsic neural circuits and induces visceral perception, such as pain. Previous studies (17,18,37) demonstrate that mechanoreceptors located in the intestinal wall play an important role in the sensory stimulus-response function. From animal studies, it seems evident that some receptors have a high threshold to mechanical stimuli and an encoding function that is evoked by stimuli within the noxious range. Other receptors have a low threshold to mechanical stimuli and an encoding function that spans the range of stimulation intensity from innocuous to noxious (3). Furthermore, some evidence obtained in animal studies indicates that the mucosal nerve endings act as rapidly adapting mechanoreceptors, whereas the intramuscular endings act as slowly adapting mechan...

Background: Visceral pain is a major clinical problem. The aim of the present study was to compare the pain and biomechanical responses to standardized distension of the human colon. Methods: The relation between pain intensity and pressure, cross-sectional area (CSA) and tension-strain relations of the rectum and sigmoid colon were studied in 11 normal subjects following standardized distension using impedance planimetry. The bag was inflated stepwise with pressures up to 6 kPa. The subjects, who were blinded for the distension procedure, rated their pain intensity using an aggregate visual analogue score (VAS) combining the intensity of the feeling of air, urge to defecate and pain. Results: The distensions produced an initial rapid increase in CSA followed by a phase of slow increase until a steady state CSA was reached after 0.5–1 min. Several phasic contractions (observed as short-term decreases in the CSA) were recorded in the rectum from the end of the rapid phase to the end of distension at pressures from 1 to 5 kPa. The CSA in the rectum and sigmoid colon was 3,706 ± 426 mm² and 2,305 ± 426 mm² at the maximum bag pressure of 6 kPa (F = 52.4, p < 0.001). The tension-strain relation did not differ between the normal rectum and sigmoid colon. The VAS score for every modality (air, defecation and pain) revealed an increase in intensity as a function of pressure. The VAS score in the rectum and the sigmoid colon as a function of tension and strain did not show any differences. Conclusions: The biomechanical properties in the sigmoid colon and rectum were alike. For a given wall tension and circumferential strain the sensibility seems equal in the rectum and the sigmoid colon. The observed difference in perception between the two segments was related to the greater CSA in the rectum.