Non-invasive determination of the distribution of cardiac output in man at rest and during exercise.

The distribution of cardiac output, as expressed by the regional uptake of thallium-201 following injection, has been studied by whole body scanning with a gamma-camera in six healthy persons and eight patients with aortic valvular disease. In the patients, cardiac output at rest and during exercise was also measured by the dye dilution technique. Combining the values of cardiac output and regional thallium uptake enabled the calculation of organ blood flow. The myocardial uptake of thallium at rest was 3.2 +/- 0.32% in the control group, which is significantly lower than 8.3 +/- 1.52%, found in the patients. The corresponding values measured in the kidneys were 12.5 +/- 1.91% in the healthy subjects and 7.1 +/- 0.50% in the patient material. Myocardial uptake increased and kidney uptake decreased in both groups following injection at peak exercise. Thallium uptake in the legs increased from about 13% at rest to about 39% at exercise in both groups. Distribution of thallium after injection at peak exercise did not, however, vary significantly between the two groups in the kidneys, abdominal area or the legs. Further methodological work is required before it can be ascertained to what extent the regional thallium uptake reflects the distribution of cardiac output. We nevertheless propose that the technique should be explored further, since it appears to be a simple non-invasive means of visualizing the distribution of the cardiac output in man under certain conditions.