A figure of merit for catheter sampling systems.

The distortion of indicator dilution curves by catheter sampling systems is predictable from theoretic considerations based on laminar flow. Over a wide range of catheter and flow parameters, deductions can be made regarding distortion, by the arterial system or by sampling catheters, of indicator dilution curves coming from an idealized pump. A figure of merit for the sampling system is given by the volume of the catheter divided by twice the flow rate. This number should be less than the time in which significant changes in indicator concentration occur, i.e., the interval between pump strokes, if significant distortion of the indicator dilution curve is to be avoided.