Theoretical and practical requirements for the valid measurement by indicator-dilution of regurgitant flow across incompetent valves

A theory is presented for the measurement of regurgitant flow across an incompetent valve hy injection of indicator distal to the valve and recording of time concentration curves proximal and distal to the valve. The conditions which must be met for valid measurements are examined and demonstrated by a functioning mechanical model of the heart. The method is valid regardless of the size of the residual volumes or degree of mixing with these volumes if a representative sample of the concentration of indicator in the blood moving across the valve in both directions is obtained. ALTHOUGH attempts have been made toestimate regurgitant flow across incom-petent valves,1"" ' critical analysis of the theo-retical and technical conditions necessary for valid results has not been presented. Accurate quantitation of the regurgitant flow across an incompetent valve is theoretically possible by indicator-dilution technics if the indicator is injected distal to a valve and time concentra-tion curves recorded at proximal and distal sites. Woodward et al.1 have used this method to estimate mitral insufficiency but they did not attempt to quantitate the actual volume of flow. Conn and Heiman4 ' r> have applied tliis method of injection and sampling to the estimation of regurgitant flow but the theory and conditions necessary for valid results have not been presented. This paper presents a theoretical method for quantitating regurgi-tant flow, independently of residual volumes, and examines by means of a mechanical model the conditions which must be met for the ac-curate application of any such method. The use of a model for the examination of a physiologic problem such as the one now under consideration serves several purposes. It provides a system to which the theories can be applied under rigidly controlled condition