The sequential measurement of ventricular volumes and cardiac output by radionuclides

A method is described which allows sequential measurements of absolute ventricular volumes from a single intravenous injection of 99 Tc m -labelled human serum albumin. The indicator dilution curve detected by a gamma camera is used to make the initial determination of cardiac output and stroke volume, and to calibrate the left ventricular end-systolic and end-diastolic volumes determined from subsequent gated blood pool imaging. Further changes in left ventricular end-diastolic volume can be related to changes in the end-diastolic counts. Thus each measurement of ejection fraction can be used to determine absolute changes in ventricular volume, stroke volume and cardiac output. In 12 patients resting, repeat measurements of end-diastolic volume showed no significant difference (coefficient of variation 2.4%). In 6 normal subjects the infusion of isoprenaline (2 mu g min -1 ) caused a significant increase (P<0.01) in cardiac output and ejection fraction and a significant decrease (P<0.01) in end-diastolic volume. Propranolol (0.14 mg kg -1 ) caused a significant decrease in stroke volume and cardiac output. The relationship between stroke volume and end-diastolic volume was depressed.