A method for measuring systolic and diastolic microcirculatory red cell flux within the canine myocardium

Background. Knowledge of the patterns of movement of red cells during the cardiac cycle in the microcirculation within the contracting myocardium is largely unknown. We describe a method of making such measurements in the canine myocardium using the technique of laser Doppler velocimetry. Methods. A lensed 100 μm fiber-optic probe was inserted into the beating myocardium at various sites. Using an ultra-stable laser and achieving measurement stability by heterodyning the laser light and reflected light from the tissue, it was possible to obtain a stable high quality measurement of predominately red cell movement in the microcirculation. Results. Unique regional patterns of red cell movement within the myocardium were observed. Epicardial flux was continuous with peaks while endocardial flux was predominately diastolic. Stopping flow in the epicardial artery for 5-6 s demonstrated that red cell movement continues in the microcirculation with some reduction followed by a delayed reactive hyperemia. Modeling demonstrates an important role for the small coronary veins in control of microcirculatory red cell movement. Conclusions. It is possible using laser Doppler velocimetry to measure red blood cell flux in the beating canine myocardium. Such measurements demonstrate a high degree of complexity which is not reflected in epicardial coronary arterial or venous flow.