Considerations of the application of indicator dilution methods to the measurement of the flow rates of fluids.

In circumstances when the flow velocity of a fluid non-homogeneous, difficulties arise in the application of the familiar indicator dilution equations. These and other relevant relationships have therefore been derived from first principles in order to clarify the conditions in which they may be expected to apply. It is shown that the method of introduction of the tracer into a fluid stream as well as its method of measurement are important factors, and the implications of these results for biological measurements are discussed. Illustrations are provided of the indicator dilution curves which are likely to be obtained under conditions of laminar fluid flow in a straight tube and when the diffusion of the tracer can be neglected.