Electronic circuitry automatically calculates cardiac output. This computer is used for basic research in physiology and as a diagnostic instrument by doctors

Mc Cullough, C. E.

English

NASA Technical Reports Server

January 1966
	
Brief 66-10006 
NASA TECH BRIEF	 jar 
NASA Tech Briefs are issued to summarize specific innovations derived from the U. S. space 
program and to encourage their commercial application. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Computer Circuit Calculates Cardiac Output 
Exponential Portion 
01 Oriciinal Curve	 Input 
AT = A 1 + A2 
Actual 
A1
- - -
	 Extrapolated 
S
Exponential A 2 -	
- --
	 Time 
t=0	 ti 
The problem: To provide a simple automatic method 
of calculating cardiac output, which is defined as the 
blood volume per unit time and expressed in liters per 
minute. Typical time curves are derived and plotted 
from the output of a densitometer in the indicator dilu-
tion method, or a count-rate meter in the surface 
counting method. Previously, an extrapolated ex-
ponential curve derived from the time curve was 
plotted on semilog paper, and the area between the 
curve and baseline was calculated with a planimeter. 
The solution: Electronic circuitry that automatically 
calculates this area under the curve and thereby elimi-
nates the laborious manual manipulations. 
How it's done: The circuitry calculates the total area 
A beneath the curve by summing the areas Aland 
A2. Relay R closes at the onset of the curve and opens 
at t i, which is an arbitrary point on the exponential 
portion of the original curve. Control of the opening 
of R can be by any convenient means provided that 
tj is always on the exponential portion of the origi-
nal curve. When R opens, the voltage E t, ( the voltage 
at point ti) is automatically stored on a capacitor. 
Because an exponential curve becomes a straight line
Integrator______________________ 
	
For A1	 I	 At	 Summing	 AT Junction 
	
Storage of	 Ganged	 A2 
Potentiometers I 
Log	 Differentiator	 Storage of 1 Amplifier 
when plotted on log paper, the output of the log ampli-
fier is a ramp function for the interval over which the 
input is an exponential time function. Also, because 
the derivative of a ramp function is a constant, the 
output voltage of the differentiator is proportional to 
a during the interval of the exponential. Since the 
maximum value of the downslope occurs during this 
interval, a may be stored by charging a capacitor 
through a diode to the maximum value of the output 
voltage from the differentiator. 
By using cathode followers for isOlation, output 
voltages proportional to Eta, and a may be obtained 
without discharging the capacitors. Then, using a 
ganged potentiometer, these voltages may be divided 
to produce an output voltage proportional to A2. The 
summing junction adds this output to A 1 to produce 
a voltage proportional to the total area beneath the 
extrapolated curve. 
Using similar techniques, the other parameters 
necessary for the determination of cardiac output 
are measured and fed into the computations and, with 
appropriate calibration procedures, computer output 
will indicate cardiac output directly in liters per minute. 
(continued overleaf) 
."
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19660000006 2020-03-11T17:33:07+00:00Z
Notes:	 Patent status: Title to this invention has been waived 
1. This invention should prove to be a valuable toot	 under the provisions of the National Aeronautics and 
for basic research in physiology.	 Space Act (42 U.S.C. 2457 (f)). to Kaman Aircraft 
2. This invention shows promise for use in doctors'	 Corporation. P.O. Box 9431, Austin 56. Texas. 
offices as a diagnostic instrument. 	 Source: Charles E. McCullough of 
Kaman Aircraft Corporation under 
contract to Manned Spacecraft Center 
MSC-274)
S 
Brief 66-10006	 Category 01


Computer circuit calculates cardiac output

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