Continuous measurement of intestinal mucosal blood flow by laser-Doppler velocimetry

Abstract

To measure blood flow in the intestinal mucosa a laser-Doppler flowmeter that consists of a helium-neon laser, an electronic circuit and a pair of fiberoptic light guides that conduct laser light to the tissue and carry the backscattered light to a photodetector was built. Because light scattered by moving red blood cells experiences a shift in its frequency, blood flow was measured by detecting the mean Doppler frequency. In isolated loops of canine small bowel, the perfusion pressure was raised and the increases in laser mucosal blood flow were significantly correlated with total blood flow measured by an electromagnetic probe. During infusions of isoproterenol (a selective vasodilator of the mucosa), laser mucosal blood flow increased before total flow increased. Similarly, adenosine (a selective dilator of the muscularis) increased total flow, whereas local mucosal blood flow fell or was unchanged. In addition, reactive hyperemia was sometimes observed in the mucosa but not in the muscularis. The laser-Doppler technique measures blood flow in the surface tissue and dose not reflect blood flow throughout the other tissues of the bowel wall. Instrumental problems identified in this study were the difficulty of calibrating the laser mucosal blood flowmeter in absolute units, the uncertainty of the volume of tissue in which local mucosal blood flow is measured and the problem of maintaining contact between the optical probe and the tissue. The method still holds great promise because it can detect small ischemic areas, because it could be used in combination with endoscopy and because it yields a continuous measurement of blood flow in either the muscularis or mucosa.