The fractional distribution of the cardiac output in man using microspheres labelled with technetium 99m

To investigate the distribution of organ blood flow in patients we have developed a method of quantitating the whole-body fractional distribution of 99Tcm-labelled microspheres. The microspheres were injected into the left ventricle in nine patients with normal cardiac indices (greater than 3 1/min/m2; Group A) and 11 patients with low cardiac indices (less than 2.51 l/min/m2; Group B). The fractional organ content of the total injected dose was estimated following correction for geometry and transmission using a gamma camera. Cerebral blood flow was 579 +/- 163 ml/min (mean +/- SD) in Group A and 593 +/- 158 ml/min in Group B (p not significant (NS)). Myocardial flow in Group A was 266 +/- 82 ml/min and in Group B was 237 +/- 57 ml/min (p, NS). Total renal blood flow was 749 +/- 161 ml/min in Group A and 614 +/- 181 ml/min in Group B (p less than 0.01). There was a negative correlation between cardiac index and the percentage of the cardiac output distributed to brain (r = -0.70, p less than 0.01), heart (r = -0.67, p less than 0.01) and kidneys (r = -0.47), p less than 0.05). Low output cardiac failure is, therefore, associated with relative preservation of cerebral and myocardial blood flow and, to a lesser extent, of renal flow. A similar technique using dual labelling would allow an accurate estimation in individual patients, of the change in organ blood flow associated with transient alterations in cardiac output states.