Radiocardiographic evaluation of left ventricular function after inhalation of C15O2

Inhalation of C15O2 delivers a bolus of labelled water into the pulmonary veins and the left atrium; analysis of the left ventricular curve provides an easy method for the evaluation of left ventricular function. the patient was seated before six collimated probes positioned toward the lungs. An additional probe was directed toward the heart in a modified 15 to 20 degrees left anterior oblique projection. One to two mCi C15O2 was administered per study. The left ventricular curve was analysed and the ejection fraction was calculated using a new method. The background was first calculated for the cycle with the largest diastolic counts using characteristic points of the curve before and after transit of the indicator through the left ventricle. For the other cycles, the background was considered to be a constant fraction of the end-diastolic counts. The left ventricular ejection fraction was obtained for each cycle after corresponding background subtraction as the ratio of diastolic activity minus systolic activity over diastolic activity. The ejection fraction thus determined in 20 patients was highly reproducible from beat to beat and from study to study in the same patient (r = 0.97 and 0.96). It corresponded closely to the ejection fraction determined using a camera-computer system (r = 0.92). We conclude that C15O2 inhalation is an easy, rapid, reproducible and attractive method to assess left ventricular function.