Multimodal pain stimulation of the gastrointestinal tract

Table 1 Multimodal comparison of clinical experimental data obtained in the esophagus from healthy volunteers

Group	Mechanical stimuli	Heat stimuli	Cold stimuli	Electrical stimuli	Sensitization with acid
Basic data	Differences between the sensations and referred pain areas was evoked by the stimulus modalities[18]. Reliability demonstrated[19,60]. The sensation to mechanical stimulations was unaffected by relaxation of the smooth muscle[40,61]. Evidence for low and high threshold high threshold	Reliability demonstrated. Stimulus-response functions obtained[18,19,60].	Reliability demonstrated. Stimulus-response functions obtained[18,19,60].	Reliability demonstrated. Stimulus-response unctions obtained[18,19,60].	Allodynia and hyperalgesia evoked[19,26], although not consistent for mechanical stimuli (see text)[26,41]. Increased referred pain and amplitude of the nociceptive reflex indicating central hyperexcitability[19,26,46]. Acid perfusion sensitizes the oesophagus to heat but not cold, indicating sensitization of peripheral TRPV1 receptors[28,46]. Remote hyperalgesia was seen in the rectum after acid perfusion of the esophagus[20]. Hyperreactivity of contractions in esophagus, but tone was unaffected[26,46].
Gender differences	Males were more sensitive to stimulations, but an increased referred pain area was seen in females, reflecting sex differences incentral pain processing[27,46].	No differences in sensation, but the referred area was larger in females[27,46].	As heat stimuli	Males less sensitive to single and repeated stimuli (Staahl et al., unpublished).	In females, the referred pain area increased to heat after acid sensitization, but no changes were seen to mechanical and cold stimulations[46].
Pharmacologic modulation	Oxycodone was better than morphine (and placebo) in attenuating mechanical pain[59].	Oxycodone was better than morphine (and placebo) in attenuating heat pain[59].	Not done	Both morphine and oxycodone attenuated the electrically evoked pain, but there were no differences between the opioids[59].	Not done