Cold and heat pain assessment of the human oesophagus after experimental sensitisation with acid.

The aim of the present study was to investigate the effect of thermal stimulation of the oesophagus before and after sensitisation with acid. In 17 healthy subjects a stimulation bag was used to re-circulate water at 5 and 60 degrees C for up to 90 s in the lower part of the oesophagus. The area under the temperature curve was used to assess the caloric load. The thermal stimuli were repeated after perfusion of the oesophagus with acid. The evoked pain intensity and referred pain areas (at the pain threshold) were assessed. At baseline the subjects were able to tolerate less caloric load (42%) for the heat compared to the cold stimuli (P = 0.007). The heat stimuli resulted in an increased referred pain area as compared with the cold stimuli (P = 0.03). Following acid perfusion there was a selective sensitisation to the heat pain stimuli as only 36% of the initial caloric load was tolerated (P = 0.012) whereas the sensation to the cold stimuli was unchanged. After acid perfusion, the referred pain area to the heat pain stimulation increased 49% (P = 0.04) but was not changed to cold stimulation (P = 0.82). After sensitisation the words used to describe the sensations to heat pain stimuli shifted from a warmth quality towards a more burning quality in most subjects. This multi-modal sensory testing study showed that acid sensitises the oesophagus to heat but not to cold pain. This may account for the modality-specific symptoms and hypersensitivity reported in patients suffering from, e.g. gastro-oesophageal reflux disease.