An Experimental Study of Viscero-visceral Hyperalgesia Using an Ultrasound-based Multimodal Sensory Testing Approach

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.