RED-CELL FLUX DURING THE CARDIAC CYCLE IN THE RABBIT MYOCARDIAL MICROCIRCULATION

Objective: (1) To measure regional phasic myocardial red cell flux dur ing a cardiac cycle using a laser Doppler velocimeter. (2) To test the responses of regional red cell flux to a vasodilator (adenosine), a v asoconstrictor (angiotensin II), and an inotrope (isoproterenol). Meth ods: Using an anaesthetised open-chest rabbit with the pericardium int act a 140-mu m-tip fibre optic probe was placed in the left ventricula r myocardium in various locations. With the fibre in place drugs were given to alter myocardial loading conditions while red cell flux was r egistered. Results: Phasic red cell flux was similar in the epicardium to endocardium giving an average eddo/epi ratio of 1.14 in the rabbit heart. At least two peaks of increased red cell flux within a single cardiac cycle were observed. Some unique patterns for red cell flux we re observed in specialised myocardial structures. Adenosine increased red cell flux but minimally changed the pattern of phasic flux through out the cycle. Conclusions: Laser Doppler velocimetry permits the reco rding of phasic red cell flux during the cardiac cycle in the myocardi al microcirculation. Its pattern is determined by both coronary arteri al inflow and venous outflow. The pattern of red cell flux may be char acteristic for a region-probably determined by difference in tissue pr essure (attributable to the pattern of muscle fibre shortening and col lagen tethering) and changes in capillary length and density.