Evaluation of the distribution of stresses and strains in relation to distension-induced sensation in the human oesophagus is valuable for understanding oesophageal biomechanics and mechano-sensation. In 12 healthy volunteers a specially designed oesophageal bag containing an endoscopic ultrasound probe was inflated to the moderate pain level. Ultrasound images, bag pressure and perceived sensation were recorded before and after pharmacological relaxation of the smooth muscle with butylscopolamine. The oesophagus was assumed to be circular and thick-walled. Distension induced a tensile circumferential stretch, radial compression and longitudinal shortening. Both circumferential strain and stress were highest at the mucosal surface and decreased throughout the wall. The stiffness increased throughout the wall and was highest at the outer surface (P < 0.001). The decrease in stiffness in response to butylscopolamine was non-significant. The infused volume (P = 0.012) and circumferential stress (P < 0.001) were most closely associated with the distension-induced sensation (adjusted R2 = 0.88). The perceived sensation was highly individual but was unaffected by butylscopolamine (P > 0.08). The present study provides a method for computation of the stress-strain distribution throughout the wall and the mechano-sensory interaction in the human oesophagus. In the future, this may be useful for understanding of mechanoreceptor responses and generation of symptoms in visceral organs in health and in disease.

Widespread visceral hypersensitivity and the overlap of symptom complexes observed in functional gastrointestinal disorders may be related to central sensitization and neuroplastic changes. A multimodal and multi-segmental model was developed to evaluate viscero-visceral hyperalgesia induced by experimental esophageal sensitization in healthy volunteers. Twelve healthy subjects were studied using a double-blinded, placebo-controlled design. The sensitivity to mechanical and heat stimulations was assessed in the proximal esophagus, duodenum and rectum before and after perfusion of the distal esophagus with acid or saline. A special-designed probe was used allowing cross-sectional ultrasound imaging during mechanical and heat stimulation of the esophagus and duodenum. Another probe was used for mechanical stimulation of the rectum. The referred somatic pain areas to gut pain stimulations were also assessed. Following acid perfusion 11 of 12 volunteers showed increased sensitivity to one or more stimulation modalities. An overall increased sensitivity to mechanical stretch in the three gut segments was seen (P=0.0001). Posthoc analysis showed that this was mainly due to increased sensitivity in the rectum (P<0.001). No changes were seen to thermal stimulations (all P-values>0.4). The somatic referred pain area to duodenal stimulations increased (P=0.04), while it was unaffected to esophageal and rectal stimulations (P>0.3). The present method demonstrated a new approach to assess multimodal sensitivity to experimental sensitization of the esophagus and related viscero-visceral hyperalgesia. Central mechanisms can explain the remote hyperalgesia to mechanical visceral stimulation and the increase in referred pain areas. The present method may be used to explore pathophysiology and pharmacological interventions in patients with visceral hypersensitivity.

No evidence was found for GES-induced modulation of the visceral sensory system and central excitability. However, GES has been proven to modulate the central nervous system in animal studies, necessitating further human experiments in order unambiguously to establish the possible central effects of GES.

Methods based on cross-sectional ultrasound imaging may be valuable for assessment of biomechanical parameters in the duodenum in health and disease. In 12 healthy volunteers a specially designed duodenal bag containing a high-frequency ultrasound probe was inflated until the perception of moderate pain. The ultrasound images and bag pressures were recorded before and after administration of butylscopolamine. The duodenum approached a circular shape as the load was increased (P = 0.01). The tension-strain relations were exponential and the curve fitting constant alpha (stiffness) was 1.72+/-0.81 before and 1.13+/-0.22 after administration of butylscopolamine (P=0.5). In three subjects construction of stress-strain diagrams was possible. The wall thickness decreased after administration of butylscopolamine (P < 0.001). The wall thickness was nonhomogeneously distributed along the duodenal circumference, being thickest at high curvatures. In the future this may be useful for assessing the geometry, stiffness, remodeling, and mechanosensory properties in the duodenum and small intestine in health and disease.

The pain perception to distension of the oesophagus can be explained by activation of receptors responding to mechanical deformation or to distension-induced ischaemia. The aim of this study was to develop a new method for detection of changes in segmental blood flow during distension based on measurement of heat transfer. A bag was distended in the distal oesophagus of six healthy subjects followed by cooling or heating of the bag fluid to 5 or 60 degrees C. After equilibrium, the temperature was allowed to change back to body temperature. The temperature was recorded together with intraluminal ultrasound imaging, allowing assessment of the heat transfer properties at different bag volumes. The heat transfer constants were higher after heating the bag than after cooling the bag (Tukey, P < 0.05). The heat transfer constants after heating the bag decreased as function of bag volumes whereas the heat transfer during cooling was not affected by the bag volume (F = 0.9, P = 0.4). The findings indicate that segmental blood flow can be assessed indirectly by calculating the heat transfer properties. Distension induced a drop in regional blood flow. Hence, ischaemia may contribute to distension-induced pain. Furthermore, heat increased segmental blood flow and cold decreased segmental blood flow. This method may in the future be used to explore the mechanisms behind oesophageal pain.