Assessment of myocardial perfusion in the empty beating porcine heart with laser Doppler flowmetry

Laser Doppler flowmetry was applied to the empty beating heart of six pigs. Cardiopulmonary bypass was instituted and the preparation allowed continuous and simultaneous measurement of coronary sinus blood flow and local tissue perfusion. An epicardial and an intramuscular probe were used. Significant linear correlation coefficients were obtained between changes of laser Doppler signal and coronary sinus blood flow changes in all seven experiments in four animals (r from 0.71 to 0.94, p<0.005) and between laser Doppler signal and changes of extracorporeal bypass in five out of six experiments in four animals (r from 0.82 to 0.99, p<0.001). The correlation between coronary sinus flow and bypass flow of four pigs was significant (r from 0.81 to 0.98, p<0.001), the coronary flow being about 10% of bypass flow. Muscular activity of the heart contributed to the laser Doppler signal, the magnitude of this "noise level" varying between different experiments even in the same animal. A key question for the applicability of laser Doppler flowmetry to the beating heart is whether it will become possible to discriminate between flow and muscular contribution to the laser Doppler output.