Evaluation of laser Doppler flowmetry in the assessment of intestinal blood flow in cat.

Laser Doppler flowmetry with a differential detector system has been used in the assessment of blood flow in the feline small intestine. Simultaneous mucosal and serosal laser Doppler flowmeter recordings were compared with total blood flow of a bowel segment measured by an optical drop-recorder unit in 6 cats. Blood flow through the muscularis layer was estimated using the 85Kr washout technique. A correlation coefficient of r = 0.96 (mucosal recordings = 90, serosal recordings = 80, p less than 0.001) was obtained between laser Doppler flowmeter output signals and total blood flow at different levels of vascular tone, regardless of whether the flowmeter recordings were made from the mucosal or the serosal side of the bowel wall. At intense vasodilation, the flowmeters showed a tendency to underestimate blood flow. The flowmeter signals were at variance with the muscularis blood flow but were clearly correlated to the calculated mucosal-submucosal blood flow. The uneven blood flow distribution in the intestinal wall did not affect the ability of the flowmeters to reflect total blood flow from either side of the bowel wall. A calibration curve could be constructed for approximate interpretation of the laser Doppler signals in absolute flow units. However, further experiments in humans and further development of the technique must be performed to elucidate clinical applications of the method.