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

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 microg.

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.

Figure 1

Rectal mucosal blood flow in patients and controls. Flow is lowest in patients with slow compared with normal transit (p=0.044) and compared with healthy controls (p=0.015); mean bars are shown. Note relatively tighter distribution of blood flow values in slow transit patients.

Figure 2

Rectal mucosal blood flow in response to inhaled placebo, salbutamol 200 µg, and ipratropium 40 µg. Ipratropium, and not salbutamol, caused a reduction in blood flow in controls and in patients with normal transit constipation, but not in those with slow transit constipation. *p<0.05, **p<0.01.

Figure 3

Relation between rectal mucosal blood flow and radio-opaque markers retained on x ray in transit study. There was a strong inverse correlation between blood flow and number of retained markers (slower transit). *p<0.05, †p<0.03.