Analog and digital simulation of the radocardiogram Page: 2 of 25
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Renewed interest in the radionuclide angiocardiogram has been stimulated by the recent
availability of systems that combine short-lived gamma-emitting radionuclides, the scintillation
camera, and fast relatively distortion-free digital recording and digital computing. More accurate
and useful diagnostic information had been promised by this ability to rapidly record images
externally and apparently to quit itate counting rates from individual heart chambers and other
regions of the central circulation. In practice, however, it was soon found that even in the best
of circumstances the counts recorded over the various selected areas of interest are weighted
averages of several regions of the central circulation, leading to complications regarding the data
that must be collected and in the mathematical analysis of the curves obtained. The great advan-
tages of a simple, noninvasive technique are partly lost because of this complexity.
Application of the above techniques has brought out the diagnostic value of the high
frequency or beat-by-beat information [1J, which previously was largely ignored because it could
not be recorded accurately. Interpretation of this information requires a mathematical treatment
beyond that offered by classical compartment-system analysis.
In an effort to extend these radiocardiographic techniques learned with the camera to a
simple, safe bedside method for serial evaluation of cardiac function and pulmonary blood volume,
a single-probe dual-collimation system has been developed (21. In this case as well, in contrast to
the classical interpretation of the single-probe radiocardiogram, the beat-by-beat or pulsatile compo-
nent of the newer tracing assumes importance in the analysis.
Our mathematical model (81 was developed to contribute to the understanding of both the
single-probe and scintillation-camera radiocardiograms, unifying the treatment of the pulsatile
component and the overall shape of such curves. This model is an extension of ideas about beat-
by-beat ejection enunciated by such workers as Folse & Braunwald 141 and Bianchi et al. [51,
extendci and made convenient by computer mcthre and combined with our own choice of an
appropriate lung delay function.
An excellent study of the radiocardiogram from this beat-by-beat standpoint was published
by Roux et at. in 1967 [61, employing an analog computer simulation. Although their pioneering
effort had almost no influence on the studies reported here, it certainly would have if we had
known of it earlier. Their model and ours share some features, but there are also certain key
differences in approach, particularly in the handling of the atria, recirculation, and delayed
injection. We have recently made their paper available in English translation.
There are two recent key papers in which classic compartment-system analysis is used as the
basis for analog computer simulation and curve-fitting of the radiocardiogram [7,8]. These are
mentioned as modern contributions that summarize much earlier work and go far in sophisticated
handling of the gross features of the curves, but without explicit recognition of their pulsatile
Other groups have recently been making studies of the pulsatile component similar to ours
[9-141 and developing models that share some features with it. Only two of these groups (9,121
model an entire four-chambered heart with lung delay. The particular virtues of the model and
computer simulations that we present here appear to be the great simplicity of the digital com-
puter programs, easily understood and able to run rapidly on a small computer in languages like
FOCAL or BASIC, and the compactness and portability of the electronic analog simulator that
we developed to carry this capability to the bedside. These systems are proving worthwhile as
heuristic devices and teaching aids. We are beginning a study to extend their capability to
automated curve-fitting and parameter estimation using the pulsatile model. From comparisons
of this more realistic model with exponential-compartment modeling, the latter appears no
konger to be an adequate way to estimate heart chamber volumes from the flow of tracer through
the central circulation.
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Parker, H.G.; Van Dyke, D.C.; Upham, F.T. & Windsor, A.A. Analog and digital simulation of the radocardiogram, article, June 1, 1974; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc1026005/m1/2/: accessed March 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.