Microspheres of different sizes, '-"'I-labeled antipyrine (I-Ap), and 4 -KCl or 86 RbCl were injected into the aortic inflow of isolated, Langendorff, perfused, nonworking dogs hearts at blood flows of 1.3-4.8 ml/min g~'. After 15 seconds to 5 minutes, the left ventricle was sectioned into about 300 ordered pieces, and the amount of each tracer was determined. For all tracers, the relative density of deposition was generally higher in the endocardial region, except in one heart in which the aortic pressure and the total coronary flow were low. The deposition of ^-K and that of I-Ap were essentially similar in three hearts over a large range of regional variation. This finding suggests either that both tracers were distributed in proportion to flow or that a small diminution in relative density of deposition of 42 K in high-flow regions due to lower transcapillary extraction was quantitatively similar to a decrease in the residual fraction of I-Ap in these same regions due to faster washout in the first 15-30 seconds after injection. Large microspheres were deposited preferentially in regions of high flow, exaggerating the apparent heterogeneity of regional flows. The distribution of the smaller microspheres was closer to that for I-Ap or 42 K.
Following left atrial injection of indocyanine green in closed-chest, anesthetized dogs, 60 simultaneous input-output pairs of dilution curves were sampled via identical catheter sampling systems from the aortic root, C in (t), and the coronary sinus, C out (t). Assuming that C out (t) was the convolution of a transport function, h(t), and C in (t), a new deconvolution technique was used to solve for the h(t)'s which was not sensitive to noise, recirculation, or the form of h(t).The 60 transcoronary h(t)'s were observed to be unimodal, right-skewed frequency distribution functions with mean transit times, t, ranging from 3 to 7 sec. The relative dispersions (standard deviation, σ, divided by t) averaged 0.38 ± 0.05, the skewness averaged 1.40 ± 0.37 and the kurtosis averaged 6.1 ± 1.8; this means that the h(t)'s are more sharply peaked than Gaussian distributions. The fact that parameters were statistically independent of the mean transit time implied the constancy of the shape of the various h (t)'s and this was verified by the coincidence of the h(t)'s plotted as a function of t/t. This "similarity" of the h(t)'s strongly suggests that changes in the transit time through any particular vascular pathway of the coronary bed are in proportion to the changes in other parallel pathways.
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