Sensory-motor responses to mechanical stimulation of the esophagus after sensitization with acid.
OBJECTIVE
Sensitization most likely plays an important role in chronic pain disorders, and such sensitization can be mimicked by experimental acid perfusion of the esophagus. The current study systematically investigated the sensory and motor responses of the esophagus to controlled mechanical stimuli before and after sensitization.


METHODS
Thirty healthy subjects were included. Distension of the distal esophagus with a balloon was performed before and after perfusion with 0.1 mol/L hydrochloric acid for 30 min. An impedance planimetry system was used to measure cross-sectional area, volume, pressure, and tension during the distensions. A new model allowed evaluation of the phasic contractions by the tension during contractions as a function of the initial muscle length before the contraction (comparable to the Frank-Starling law for the heart). Length-tension diagrams were used to evaluate the muscle tone before and after relaxation of the smooth muscle with butylscopolamine.


RESULTS
The sensitization resulted in allodynia and hyperalgesia to the distension volumes, and the degree of sensitization was related to the infused volume of acid. Furthermore, a nearly 50% increase in the evoked referred pain was seen after sensitization. The mechanical analysis demonstrated hyper-reactivity of the esophagus following acid perfusion, with an increased number and force of the phasic contractions, but the muscle tone did not change.


CONCLUSIONS
Acid perfusion of the esophagus sensitizes the sensory pathways and facilitates secondary contractions. The new model can be used to study abnormal sensory-motor mechanisms in visceral organs.
Drewes
Asbjørn-Mohr
AM
Center for Biomechanics and Pain, Department of Medical Gastroenterology, Aalborg Hospital, DK-9000 Aalborg, Denmark. drewes@smi.auc.dk
Reddy
Hariprasad
H
Staahl
Camilla
C
Pedersen
Jan
J
Funch-Jensen
Peter
P
Arendt-Nielsen
Lars
L
Gregersen
Hans
H
D000328:Adult; D002404:Catheterization; D004947:Esophagus / Q000294:innervation* / Q000502:physiology*; D005260:Female; D006801:Humans; D006851:Hydrochloric Acid; D006930:Hyperalgesia / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology*; D010812:Physical Stimulation; D013268:Stimulation, Chemical
D006851:Hydrochloric Acid