T. J. Knopp

Regional distribution of diffusible tracers and carbonized microspheres in the left ventricle of isolated dog hearts

Microspheres of different sizes, 125I-labeled antipyrine (I-Ap), and 42KCl or 86RbCl were injected into the aortic inflow of isolated, Langendorff, perfused, nonworking dogs hearts at blood flows of 1.3–4.8 ml/min g−1. 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 42K 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 42K 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 42K.

Flow estimation by indicator dilution (bolus injection).

Indicator dilution techniques used for the estimation of flow (F), mean transit time (t), dispersion (σ), and mean transit time volume (V) in the circulation are subject to error when (1) flow is not steady and (2) concentrations are obtained by sampling at a constant rate (time averaging) rather than at rates proportional to the instantaneous flow past the sampling site (volume averaging). Using a simple descriptive model for indicator transport, the effects of simulated aortic flow or of sinusoidal flow of widely variable frequency were assessed. Errors in estimates of F, t, σ, and V are greater with bolus injections than with constant-rate injections. Errors are roughly proportional to the amplitude of variation in flow. They are maximal when the period of flow fluctuation is similar to the passage time of the dilution curve, which, for the human central circulation, is about the time for one respiratory cycle. With sinusoidal flow between 50% and 150% of the mean flow, errors were at worst up to 60% in F, 30% in t, 50% in σ, and 70% in V, with a bimodal distribution. Errors are minimal at cardiac frequencies. The troublesome lower frequencies can be avoided. Preliminary tests of a method for converting time- to volume-averaged concentrations gave encouraging results.

Transcoronary intravascular transport functions obtained via a stable deconvolution technique.

AbstractFollowing 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,Cin(t), and the coronary sinus,Cout(t). Assuming thatCout(t) was the convolution of a transport function,h(t), andCin(t), a new deconvolution technique was used to solve for theh(t)s which was not sensitive to noise, recirculation, or the form ofh(t).The 60 transcoronaryh(t)s were observed to be unimodal, right-skewed frequency distribution functions with mean transit times,

Closing capacity in awake and anesthetized-paralyzed man

\bar t

First derivative of ventricular pressure recorded by means of conventional cardiac catheters.

, ranging from 3 to 7 sec. The relative dispersions (standard deviation σ, divided by

Kinetics of blood-tissue exchange of tracers

\bar t