Indocyanine green kinetics characterize blood volume and flow distributionand their alteration by propranolol

Background and objectives: Although indocyanine green can be used to estima te cardiac output and blood volume independently, a recirculatory multicomp artmental indocyanine green model enables description of these and addition al intravascular events. Our model was used to describe the effect of propr anolol on blood volume and flow distribution in humans. Methods: Indocyanine green disposition was determined twice in four healthy adult men, once during a propranolol infusion that decreased cardiac outpu t, After injection of indocyanine green, arterial blood was collected frequ ently for 2 minutes and less frequently thereafter. Plasma indocyanine gree n concentrations were measured by HPLC. The recirculatory pharmacokinetic m odel incorporates data from both the initial transient oscillations and the later post-mixing portions of the blood indocyanine green concentration ve rsus time curves to characterize not only blood volume and cardiac output b ut also their distribution among a central blood volume and fast and slow p eripheral volumes in lumped parallel circuits. Flow through the central cir culation (cardiac output) is described by two parallel Erlang distribution functions generated by two linear chains of compartments in parallel. Results: Propranolol reduced cardiac output from 10.6 to 4.1 L/min. Most of the decrease in cardiac output was at the expense of blood flow to the fas t peripheral circuit, which represented nonsplanchnic circulation. Proprano lol also reduced the blood volume of the fast peripheral circuit by more th an half. Conclusion: Our indocyanine green model is able to derive estimates of bloo d volume and cardiac output, as well as their systemic distribution during different physiologic conditions.