ESTIMATION OF SYSTEMIC BLOOD FLOW BY INDICATOR-DILUTION TECHNIC IN PRESENCE OF CENTRAL SHUNTS

The effect of a central systemic to pulmonary shunt on indicator-dilution measurement of cardiac output was examined experimentally in dogs and analytically with a mathematical model. Simultaneous dye-dilution curves were obtained by sampling pulmonary and femoral arterial blood through paired Waters cuvette densitometers and recording systems. Indocyanine green dye was injected as a bolus in the vicinity of the right atrium. Blood flow was calculated by the usual Stewart-Hamilton approach. Twenty pairs of indicator-dilution curves were obtained from 4 control dogs. Flow measured from the femoral artery sampling site (QFA) averaged 93 per cent of that obtained from the pulmonary artery (QPA). Systemic to pulmonary artery shunts were created in 6 dogs. Shunt flow, estimated by a modification of the Fick method, ranged from 2.0 to 3.4 L./min. Twenty-seven pairs of indicator-dilution curves were obtained from this group. QFA averaged 92 per cent of QPA. Hence, the shunt had no effect on the measurement of systemic blood flow. A simple compartmental model of the circulation was constructed and computer solution of the differential equations automatically plotted. Integration of the simulated dye-concentration curve gave the area from which flow could be calculated. The presence of a central shunt changed the shape but not the area under the curve. The calculated flow in either case, therefore, is the true systemic flow. © 1968.