Studies of coronary blood flow by multiple dye dilution curves.

The indicator-dilution technique has recently been applied to the study of the coronary circulation. One of the methods which have been proposed is the estimation of coronary blood flow from dilution curves sampled from the right ventricle after the injection of radio-iodinated human serum albumin into the left ventricle or into a catheter "wedged" in a branch of the pulmonary artery (1). Another is based on the claim that coronary blood flow can be quantitated from precordial radioactivity curves (2). These observations have been challenged on both experimental and theoretical grounds (3-6). The radioactive method has been re-examined by comparing intraarterial indicator dilution curves with those obtained by surface counting from the precordium and brain (7). In this study a prolonged disappearance slope obtained from the precordium when compared to brain and artery was found which was absent when the coronary circulation was seriously impaired. It was assumed that the slow passage of a radioactive indicator through the coronary bed might be one of the factors influencing the precordial dilution curve in spite of the small total amount circulating through this vascular compartment. In the face of these uncertainties, it seemed of interest to examine the temporal relationship of an indicator dilution curve obtained from the coronary sinus with those from other intrathoracic cardiovascular sites. In the present study, paired dye dilution curves were recorded simultaneously from multiple sites in the circulation, including the coronary sinus, after injection of the indicator either into a peripheral vein or into the chambers of the left side of the heart. The time relationships of such curves