To compute the heartbeat rate from the waveform output of an electrocardiogram, a digital cardiometer with solid state circuit elements has been developed. This computes the beat every 15 seconds and visually presents the data on numerical display tubes

Mitchell, V. M.

English

NASA Technical Reports Server

November 1964	 Brief 64-10258 
NASA TECH BRIEF 
. • ______________ __________________ 
This NASA Tech Brief is issued by the Technology Utilization Division to acquaint 
industry with the technical content of an innovation derived from the space program. 
--	
- 
Digital Cardiometer Computes and Displays Heartbeat Rate 
	
Signal Conditioner 	
Multiplier 
	
Flip-Flop Reset	 Fa_
EKG Inputs 
115V AC
V 
Pulse Multiplie:	 ^
Lock 
Heart Counters 
Memories	 Memories 
.
Units	 Tens 
___ 
Time Counters 
Units	 Tens 
Square Wave
	
T 
—3V,,. Converter I	 1
Heart Rate Read 
L_____
S2 Forget 
U
200V 
Reset 
_11.-r_-	 ..Powe	 '	 [,jeaJ	 Reset 
Clock 
5V AC 
60 CPS 
	
The problem: To provide an instrument which will 	 a pulse multiplier, a memory, and numerical display 
	
compute heartbeat rate from the waveform output of
	 tubes. 
	
an electrocardiograph (EKG) and visually display the
	 The three-stage decade counter in the clock circuit 
data in beats per minute.	 counts the 60-cps pulses from the square-wave con- 
The solution: An instrument (a digital cardiometer) verter. At the count of 895 (i.e., 5 pulses less than 
 
with solid-state circuit elements which computes the
	
the number of pulses in 15 seconds =60x 15 —5), the
last heartbeat reading on the numerical display tubes

	
heartbeat rate every 15 seconds and presents the data
	 is erased. At the count of 900 (pulses in 15 seconds), 
on numerical display tubes.	
a read pulse triggers the display tube to present the 
	
How it's done: The cardiometer basically consists	 new heartbeat reading. At the count of 901, the 
	
of a source of 60-cps pulses, a clock, decade counters, 	 counters are reset, and the cycle is repeated. 
(continued overleaf) 
	
This document was prepared under the sponsorship of the National 	 this document, or that the use of any information, apparatus, method, 
	
Aeronautics and Space Administration. Neither the United States Govern- 	 or process disclosed in this document may not infringe privately-owned 
	
ment, nor NASA, nor any person acting on behalf of NASA: A. Makes	 rights; or B. Assumes any liabilities with respect to the use of, or for 
	
any warranty or representation, express or implied, with respect to the	 damages resulting from the use of, any information, apparatus, method, 
	
accuracy, completeness, or usefulness of the information contained in 	 or process disclosed in this document. 
https://ntrs.nasa.gov/search.jsp?R=19640000069 2020-03-11T17:04:22+00:00Z
The waveform from the EKG amplifier is converted 
into a short negative pulse which resets the pulse 
multiplier (a binary counting circuit). Four time 
pulses are counted for each heartbeat, so that at the 
end of 15 seconds the number displayed is the number 
of heartbeats per minute. The pulse is routed through 
an AND gate which is held open until the eighth pulse 
enters the counter portion of the pulse multiplier. (The 
output of the AND gate also goes to an output circuit 
consisting of a single flip-flop. The odd-numbered 
pulses 3, 5, and 7, are the output.) At the count of 8, 
the multiplier feeds back a pulse to the AND gate and 
deactivates it until another heartbeat resets the system 
and opens the gate. 
The four pulses per heartbeat are fed to a three 
stage decade counter (heart counter), and the output 
for each number in the counter is fed to an AND 
circuit. The other input to the AND circuits is a 
common read voltage. When IS seconds have passed, 
the read voltage is removed from one pulse length. 
The two or three AND circuits which are keyed by the 
counter at that instant will trigger silicon-controlled 
rectifiers to act as latching relays for the numbers 
selected by the counter. When the read voltage is
replaced, the other AND circuits of the memory are 
locked. (The display remains until a cancelling signal 
is sent at pulse number 895 which momentarily inter-
rupts the B+ from the display tubes). This action 
resets the memory circuits and removes the old 
reading. 
Notes: 
I. The cardiometer should have application as a 
medical diagnostic and teaching aid. 
2. A related innovation is described in NASA Tech 
Brief B64-10003, March 1964. Inquiries may also 
be directed to: 
Technology Utilization Officer 
Manned Spacecraft Center 
P.O. Box 1537 
Houston, Texas, 77001 
Reference: B64-10258 
Patent status: NASA encourages commercial use 
of this innovation. No patent action is contemplated. 
Source: Virden M. Mitchell 
(MSC-93) 
Brief 64-10258	 Category No. 01


Digital cardiometer computes and displays heartbeat rate

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