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A major determinant of oxygen transport to the myocardium is the time spent by the erythrocytes (red blood cells [RBCs]) traversing the microcirculation. Although it has been shown that the myocardium has regional differences in blood volume, blood flow, metabolism, and sensitivity to ischemic injury, the regional distribution of RBC transit times through the myocardial capillaries has not been previously measured. The present study was designed to measure the regional myocardial capillary RBC transit time by a new technique to determine whether there are regional differences in the capillary RBC transit time in the normal resting heart. Anesthetized open-chest male New Zealand White rabbits (3.0-3.7 kg, n=8) were studied. Regional myocardial blood volume was determined using chromium-51-labeled RBCs, and regional blood flow was measured using a reference flow technique and a left atrial injection of 15-gm-radiolabeled (gadolinium-153, 10-20 gCi) microspheres. Capillary blood volume was determined by multiplying the regional blood volume by the histologically determined fraction of the total blood volume that was in the capillaries. Capillary RBC transit time was calculated as the quotient of capillary blood volume and blood flow. The myocardial capillary blood volume was the same in the endocardium and the epicardium (4.67±0.67 ml/100 g for endocardium versus 4.52±0.70 ml/100 g for epicardium, p=NS), whereas myocardial blood flow tended to be greater in the endocardium (6.09±0.73 ml/sec per 100 g for endocardium versus 5.47±0.75 ml/sec per 100 g for epicardium), although this was not statistically significant. Myocardial capillary RBC transit times ranged from 0.22 to 2.58 seconds with a mean of 0.89±0.13 and 0.83+±0.13 seconds and a median of 0.72 and 0.70 seconds in the epicardium and endocardium, respectively. We conclude that there are no regional differences in the myocardial capillary RBC transit time in the normal heart at rest. (Circultion Research 1993;72:187-193) KEY WoRDs * erythrocyte transit time * oxygen transport * myocardium I ncreases in myocardial oxygen consumption in response to modest levels of work are generally accomplished by corresponding increases in coronary blood flow.12 At more extreme levels of cardiac work, increases in coronary flow are insufficient, and increased extraction of 02 from the blood may contribute up to 40% of the increased myocardial oxygen consumption.2 A major determinant of the transport of 02 from blood to tissue is the time spent by erythrocytes (red blood cells [RBCs]) passing through the capillaries, the capillary RBC transit time.3-9 The capillary transit time in a given region of myocardium is dependent on the blood volume and blood flow in that region, both of which may vary significantly.1,'0" l If the capillary RBC transit time also shows regional differences, it might be an important factor contributing to the well-known regional variability in myocardial susceptibility to ischemia.12 Although the RBC transit time in cardiac muscle has been previou...

We propose a set of equations validated using IVUS and based on gender- and segment-specific normal values for coronary angiographic size and shape that markedly improves the sensitivity of the coronary angiogram for detection of abnormalities. The method should replace the unfounded practice of labeling coronary angiograms as "normal" based solely on the failure to detect focal stenoses.

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