Estimation of coronary blood flow by washout of diffusible indicators.

In 13 canine hearts, 158 disappearance curves for Xe and antipyrine-I, given by intra-arterial slug injection, were recorded at a wide range of perfusion rates. Flow rates (ml/100 g/min) calculated from these curves by a variety of methods were compared with measured flow rates (F) per weight of perfused tissue. Perfusion of isolated, supported hearts and of anterior descending coronary arteries in open-chest dogs provided similar data. The semilogarithmic slope of curves from apex or whole heart decreased with time, particularly at high flow rates. There was a small, consistent difference in shape between antipyrine and xenon curves, suggesting that radioactivity in fat contributed somewhat to this tailing. Estimation of flow rate from the steepest semilog slope yielded an average value of 1.1F for all rates; estimation from slope at 30% of peak radioactivity gave 0.9F. The curves were closely described by a two-exponential equation which gave flow estimates of 0.95F when collimation limited the observations to the heart apex, and lower values when the whole heart was observed. Peak height/area methods gave values of approximately 0.75F in spite of various compensations for the impossibility of recording the curve until radioactivity = 0.