Basic concepts in the determination of vascular volumes by indicator-dilution methods.

• The Ralculation of central (thoracic, pulmonary) blood volume from indicator-dilution data was introduced by Stewart' and developed and applied mainly by Hamilton and his group.The so-called classical Stewart-Hamilton method was based on the premise that the product of flow rate and mean transit time defined the volume of the flow channels. Originally intuitive, this premise has recently been formally validated by Meier and Zierler. The classical method has been widely used, sometimes with misunderstanding.' 7 More recently, a mixingchamber model developed to account for the form of the indicator-dilution curve has led to the introduciion of a "slope-volume" method for describing pulmonary blood volume. Further attempts to partition the central blood volume into its cardiac and pulmonary components have led to the development of an indirect mathematical method based on the mixing-chamber model as well as to more direct experimental methods utilizing special locations of injection and sampling sites.' ~ It is the purpose of this paper to examine the fundamental concepts upon which these several methods are based. I shall begin with the classical method.