A transfer function analysis of coronary and renal circulation calculated from upstream and downstream indicator-dilution curves.

A method has been developed for computing the distribution of blood transit times (transfer function) from indicator-dilution curves recorded from upstream (aorta) and downstream (pulmonary artery, renal vein and coronary sinus) circulator sites in mongrel dogs. The method employs a Fourier series transformation of the upstream and downstream curves and yields a time-domain transfer function which is independent of recirculating dye particles. Discontinuities, created in the upstream and downstream indicator curves by the termination of sampling (120 sec postinjection), are removed by a tail terminating procedure which employs normal and lagged normal density distributions. The transfer functions computed for the trans-renal and trans-coronary circulations and their relationship to the systemic circulation dispersion patterns are shown under control conditions (pentobarbital anesthesia) and during intra-aortic infusion of angiotensin, acetylcholine and adenosine triphosphate. These distribution patterns reflect the response of the vascular system to the drugs and demonstrate, to a limited extent, the role which different vascular beds have in the cardiovascular mixing process.