• A M Drewes, J Pedersen, W Liu, L Arendt-Nielsen, and H Gregersen.
• Laboratory for Visceral Pain and Biomechanics, Dept. of Medical Gastroenterology, Aalborg Hospital, Denmark. drewes@smi.auc.dk
• Scand. J. Gastroenterol. 2003 Jan 1;38(1):27-35.

BackgroundThe relation between mechanical distension of the gut and the sensory response is poorly understood. The current experimental study aimed to examine the sensory response in the human oesophagus during on-line recording of the luminal pressure, cross-sectional area (CSA) and sensory rating using different distension rates before and during relaxation of the smooth muscle.MethodsAn impedance planimetric probe for bag distension of the oesophagus was used in 13 healthy subjects aged 43 +/- 15 years. Ramp distensions were done with an electromechanical pump using infusion rates of 10, 25 and 50 ml/min, with and without relaxation of the smooth muscle with butylscopolamine. The sensory intensity was measured using a 0-10 visual analogue scale (VAS), with 5 as the pain threshold. The pump was reversed at 8 on the scale, corresponding to medium pain intensity, and the pressure, volume, tension and CSA were evaluated. Finally, three isovolumetric experiments where the CSA was held constant for 2 min at initial VAS ratings of 3, 5 and 7 were performed.ResultsA total of 104 distension profiles were investigated. The volume at maximal pain intensity (VAS = 8) increased as a function of the distension rate (P < 0.001), whereas the pressure, tension and CSA were not affected. When the smooth muscle was relaxed, there was a 29% fall in pressure at maximal pain intensity (P = 0.004), a 27% fall in tension (P = 0.003), whereas CSA did not change (P = 0.3). When the pressure was recorded as a function of the sensory intensity, there was an exponential increase after the pain threshold was reached, whereas the stimulus-response functions for tension, volume and CSA were nearly linear. In the isovolumetric experiments the ratings during the three sensory intensities were the same in the individual subjects, but the between-individual pain response was variable, probably reflecting individual differences in adaptation/central integration.ConclusionsThe study allowed us to assess the strain-rate dependency of both perception and biomechanical properties in the oesophagus. It was demonstrated that the pain response was related to the CSA (and hence strain), independently of the contractile state of the muscle and biomechanical behaviour of the tissue. The findings support the fact that the pain-sensitive mechanoreceptors in the human oesophagus depend on circumferential wall stretch rather than on pressure, tension and volume. The model should be used in future studies to investigate whether changes in strain are responsible for the oesophageal sensation in health and disease.

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