Electronics for this system may be chosen so that complete calculation and display may be accomplished in a few milliseconds, far less than even the fastest heartbeat interval. Accuracy may be increased, if desired, by using higher-frequency timing oscillator, although this will require large capacity registers at increased cost

Rasquin, J. R.

Smith, H. E.

Taylor, R. A.

English

NASA Technical Reports Server

March 1974	 B73-10477 
NASA TECH BRIEF 
Marshall Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Cardio tachometer Displays Heart Rate on a Beat-to-Beat Basis 
(0.5 S if 120 Beats/Minute)
Note: Figures in parentheses show typical 
(120/Minute)
	 0	
.11.1 Gate I	 values for heartbeat of 120/minute. 
I	 I(1/120 Minute) 
On	 Off Computation 
Oscillator	 Register A
	
Register B 
1600 Hz
(800)	 (800 Down to 0) 
Countdown ]	 Register D 
Oscillator	 96,000-n (A) 
150 kHz	 (96,000-n 800) 
Reset 
Cardiotachometer Block Diagram
Counter 
C 
Output  Pulse Rate Display 
only at 
"B" = 0 
Output
Only at

= 0 
The problem: 
There are frequent times or instances in hospitals 
and during medical examinations when it is desirable 
to have a continuous numerical display of a patient's 
heart rate. To date, analog devices have been available 
for this purpose, but they are subject to drift and are 
susceptible to noise. 
The solution: 
A cardiotachometer has been developed which pro-
vides a direct digital display of a patient's heart rate. 
How it's done: 
The cardiotachometer block diagram is shown in the 
figure. In this case, the processing is illustrated for a 
heart rate of 120 pulses/minute. As shown, the, input 
is fed to the gate which turns on for one heartbeat 
interval and passes pulses from the oscillator to register
A, during that interval. At the end of this interval 
after the gate is off, register A dumps into register B. 
Register B automatically counts down to zero, at which 
time the B = 0 pulse is counted in counter C, and also 
causes register A to dump into register E. 
Register D is preset to 96,000 at the beginning of 
each complete computation period It is counted down 
at the same rate as register B and so limits the number of 
cycles to 96,000-n (A). Thus, the system cycles n times 
before being reset (n = 120 in the example). Counter C. 
counts the number of cycles (n) and displays this 
figure as the pulse rate. The relatively long display 
period used eliminates the rapid flicker that I would 
result, if the rate were displayed on a beat-to-beat 
basis for a patient with rates above 100 beats/minute. 
The electronics for this system may be chosen so that 
the complete calculation and display may be ac-
complished in a few milliseconds, far less than even the 
(continued overleaf) 
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Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19730000477 2020-03-17T07:31:27+00:00Z
fastest heartbeat interval. Accuracy may be increased, 
if desired, by using a higher-frequency timing oscillator, 
although this will require large capacity registers at 
increased cost. 
Since variations in heart rate may be of interest, an 
additional C* counter or register can be included, which 
will hold the previous heart rate. This could be counted 
down by the new heart-rate counts to counter C, so that 
at the end of the calculation counter C* would hold the 
difference in beats/minute. This difference can be read 
from a digital display or supplied to a simple digital-to-
analog converter, and the resulting voltage displayed by 
a meter or as a trace on a recorder. If desired, the heart 
rate displayed in counter C can also be converted to an 
analog voltage. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Code A&PS-TU 
Marshall Space Flight Center, Alabama 35812 
Reference: B73-10477
Patent status: 
This invention has been patented by NASA (U.S. 
Patent No. 3,773,038). Inquiries concerning nonexclusive 
or exclusive license for its commercial development 
should be addressed to: 
Patent Counsel 
Marshall Space Flight Center 
Code A&PS-PAT 
Marshall Space Flight Center, Alabama 35812 
Source: J. R. Rasquin, H. E. Smith, 
and R. A. Taylor
Marshall Space Flight Center
(MFS-20284) 
B73-10477	 Category 05,02


Cardiotachometer displays heart rate on a beat-to-beat basis

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