Analog and digital simulation of the radocardiogram Page: 4 of 25
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Quantity of tracer in lung
Iii the general case the lung transit-time distribution must be convoluted on the input from
the RV.. In our discrete-variable approximation this convolution is given by
qi 'I- k . H*i-k)
and q'= qi.
q; is the quantity of tracer in the lung, where i indexes the cardiac cycles. Ik is the input from
RV systole during any previous kth cycle. H* is the lung residue-function described above. q'
is used to indicate the value at ventricular end-diastole in contrast to q at ventricular end-systole.
The lung output to the LA is given by
r,:. q;.1 -,qi;+ I,
where i- 1,2,8,.... and qo - 0,
For the case of a single oneabeat injection direct into the lung, the above simplifies to
and r - qi.I - q
In this case the values of i and Hrneed not be stored by the program at each cycle for later use,
as is necessary for the convolution.In connection with one-beat injection direct into the RA, we have
described a mathematical device that can take advantage of this simplification . It consists of
rearranging the order of lung and heart chambers for calculational purposes, putting the lung first
for part of the calculation. It results in reduced computer time and core storage requirements that
may be important in some small-computer applications. An example of this rearrangement can be
found in the sample program, Fig. 3.
The simplest set of parameters required as input to the model consists of the following six
numbers: four ejection fractions, one for each heart chamber, plus the two parameters of the
tang delay, often specified as its mean transit time and the factor n (number of compartments in
series) for the shape of the,delay.
Anotil useful set of parameters that specifies essentially the same information about the
model, but which isoften closer to the clinical interest of the user, is the following set of seven
psMbers: the stroke volume, four end-diastolic volumes, one for each heart chamber, plus two
parameters for the lung delay, often specified as the lung blood volume and the shape factor, n.
From these the program easily calculates the primary set of parameters initially. We have not
often found it usefb:l to specify cardiac output and heart rate as input parameters, since only
their ratio (stroke volume) is needed by the program, but this can of course be included if
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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/m1/4/: accessed March 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.