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.