Microcomputer analysis of indicator dilution curves to determine Qp/Qs.

We developed and tested, in an animal model, a method for collecting and analyzing indicator dilution curves to determine the pulmonary-to-systemic flow ratio (Qp/Qs) using a programmable microcomputer. Curves were digitized in real time by an analog to digital converter. A gamma variate curve fitting algorithm, similar to that used in nuclear cardiology, was used to determine the area under primary and recirculation portions of a single cardiogreen dye curve. A ratio of these areas was used as a measure of Qp/Qs. In an animal model simulating patent ductus arteriosus, there was close correlation of Qp/Qs measured by the Fick method and by the microcomputer method (computer Qp/Qs = 0.95 X Fick Qp/Qs + 0.22, R = 0.97, N = 14, SEE = 0.14). The computer method of measuring Qp/Qs is rapid, easily repeatable, and does not require catheter manipulation. Therefore, it may be particularly useful in the clinical cardiac catheterization laboratory for studying the effects of interventions on Qp/Qs.