Steady-state transfer function analysis of portions of the circulatory system using indicator dilution techniques

A digital computer program has been developed whereby the distribution of dye particle transit times across circulatory pathways can be found from recordings of upstream and downstream indicator dilution curves. This distribution, or transfer function is computed from Fourier series representations of the upstream and downstream indicator curves and makes possible, for the first time, the calculation of transit time distributions independent of the effects of recirculating dye. Since a discontinuity is introduced into the tails of the upstream and downstream curves at the end o£ the indicator sampling, the method requires an iterative approach in the termination of the upstream and downstream curves. The precision of the calculated distribution pattern is determined by comparison of the recorded downstream curve with the results of the convolution of the recorded upstream curve and computed transfer function. The effects of noise, bandwidth, sampling rate and aliasing have been investigated through the use of analog computer models of circulatory pathways. These studies show that the, transfer function description is limited to the bandwidth of the upstream (input) curve. Noise, or variations in magnitude and phase angle o£ input and output curve frequencies, and aliasing effects can introduce oscillations into the time-domain representation of the transfer function as does the use of too few harmonic terms. Two physiological studies are present which show the applicability of using the above method in the analysis of circulatory dispersion properties. The first study is concerned with the vascular responses (coronary, renal and systemic circuits) to the drugs adenosine triphos-phage, acetylcholine and angiotensin II, The second study shows the circulatory dispersion relationships which exist between lower extremity, renal and systemic circuits before, during and following moderate treadmill exercise. A third section of the thesis is devoted to the study of catheter-sampling distortion conditions and to the development of means of correcting for such. Transfer function relationships which describe catheter geometry configurations [bends and coils) and blood hematocrit effects are presented.""