Simultaneous counting of 85Kr in lung and myocardium during measurement of coronary blood flow.

Coronary blood flow rate (ml-min-1-100 g-1) was estimated by a) measuring pump flow into the cannulated circumflex branch of the left coronary artery and dividing by the weight of perfused myocardium and b) measuring the clearance of 85Kr following intra-arterial injection (detection with a 2-in. crystal with cylindrical collimation). Although the correlation between the two measurements was relatively high (r equals 0.90), the line best fitting the data was 85Kr flow equals 0.55 pump flow + 25.6. We tested the possibility that the discrepancy between the two methods was primarily due to the counting of 85Kr removed from myocardium and delivered to lung. Relative efficiency of lung counting versus myocardial counting was determined as well as clearance pattern of 85Kr from lung in each dog. A simple mathematical model which assumes no recirculation of 85Kr to heart allowed correction of coronary clearance curves using this information. When corrected 85Kr flow equals 1.00 pump flow + 4.1 (r equals 0.90). Thus, the major systematic cause for the discrepancy between the two measurements under the conditions of this experiment appears to be simultaneous counting of 85Kr in lung and in myocardium.