Laser Doppler flowmetry as a measure of extrinsic colonic innervation in functional bowel disease

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Abstract
BACKGROUND In functional disorders it is unknown whether disturbed function is due to an intrinsic gut abnormality or altered extrinsic innervation. AIMS To study whether measurement of mucosal blood flow could be used as a quantitative direct measure of gut extrinsic nerve autonomic activity in patients with idiopathic constipation. METHODS Seventy two patients with idiopathic constipation and 26 healthy volunteers had rectal mucosal blood flow measurements by a laser Doppler flowmetry probe applied 10 cm from the anus. Measurements were made at rest and after inhaled placebo and ipratropium 40 μg. RESULTS Constipated subjects had lower baseline rectal blood flow than controls. Patients with slow transit had lower mucosal blood flow than normal transit. The number of retained markers on x ray was inversely correlated with blood flow. Ipratropium reduced blood flow compared with placebo, reduced it less in constipated patients than controls, and reduced it less in patients with slow compared with normal transit. Constipated patients, not controls, showed a significantly attenuated RR interval (the interval between successive R waves on the ECG) variability, and blood flow correlated with vagal function. CONCLUSIONS Laser Doppler mucosal flowmetry is a gut specific, quantitative measure of extrinsic autonomic nerve activity. The technique has shown that patients with idiopathic constipation have impaired extrinsic gut nerve activity, and this is more notable in those with slow transit. The degree of slow transit correlates with the degree of impaired extrinsic innervation.