System measures electrocardiographic potentials to produce precise quantitative measurement of changes that occur in individual's cardiac function. System is rugged, built to sustain extremes of temperature, pressure, humidity, shock, and vibration. It can also be used in pure oxygen environment without danger of combustion

Costello, M.

English

NASA Technical Reports Server

/ 
November 1973	 B73-10401 
•
	 NASA TECH BRIEF 
Lyndon B. Johnson Space 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. 
Vectorcardiogram 
.
,A typical biomedical system for monitoring cardiac 
parameters consists of several separate units, each 
having specific functions. Although a system with 
separate units has some advantage over a completely 
integrated system, such as easy replacement of units to 
add technical improvements, an integrated system is 
much more compact and convenient to operate. 
An integrated vectorcardiogram (VCG) system was 
developed which incorporates the functions of all the 
separate units and provides easy handling and accurate 
performance. The VCG measures the electrocardiographic 
potentials to produce a precise quantitative measurement 
of the changes that occur in the individual's cardiac 
function. This measurement is accomplished by summing 
seven separable electrocardiographic potentials through 
orthogonal vectors of heart activity. These orthogonal 
vectors are individually conditioned by a multistage 
pass-band amplifier which provides three significant 
data outputs (vectorial). 
In addition to the VCG data, the vectorcardiogram 
system provides two continuous readouts of heartrate: 
One, a three-numeral light-emitting diode (LED), digital 
display useful for on-the-spot monitoring of the subject's 
heartrate; and two, an analog output useful for keeping 
long-term records of the subject's heartrate activity. 
The system has built in safety. Each electrode that 
attaches to the subject's body is protected with an 
electroshock protection circuit (ESP). These ESP circuits 
are specially designed, miniature, hybridized circuits that 
limit the current that can pass through the subject's 
body to less than 200 pA. The ESP circuits will 
perform to this requirement if the , subject contacts a 
potential of up to 200 volts peak at any frequency 
from dc to 1000 Hz. The ESP circuit requires no 
power supply and therefore is always active. 
The VCG was designed to make operation more 
convenient and practical than the previous systems.
Subjects located some distance away from the system 
can be monitored remotely. A switch is provided for 
instant calibration which can be performed each time 
the VCG is used.' Another switch is used to measure 
the electrode-to-skin impedance of each electrode. The 
three channels of VCG data are suitable for recording on 
a storage oscilloscope, strip chart recorder, vector scope, 
or magnetic tape. The subject's heartrate is automatically 
computed (averaged over 5 heartbeat periods) and 
continuously displayed on a three-numeral LED digital 
display. The electrodes used with the VCG are reusable 
and require minimal skin preparation for application. 
Recovery time from transients due to fluctuations in 
operating voltage or signal strength is less than 5 
seconds. 
The VCG outperforms previous systems in several 
parameters. Its high input impedance (greater than 40 
megohms) assures accurate sensing of the electro-
cardiographic potentials at each electrode. Its low 
output impedance (less than 5 ohms) allows the VCG 
outputs to be displayed on a variety of equipment. All 
signals picked up from the body are amplified with 
differential amplifiers to minimize data degradation due 
to noise artifacts. System noise is less than 10 pV, and 
harmonic distortion is less than 1%. The gain of each of 
the three channels is individually selectable, and the 
phase of all channels is matched to within 3 0
 at all 
the gain settings. The system also has circuitry built in 
to provide good high-frequency noise rejection. In 
addition, an automatic transient recovery circuit is 
included that turns on when high voltage transients 
occur on the input (higher than the ability of circuit 
to reject). 
The VCG is very rugged, built to sustain extremes of 
temperature, pressure, humidity, shock, and vibration. 
It can also be used in a pure oxygen environment without 
danger of combustion.
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
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=19730000401 2020-03-17T07:28:32+00:00Z
Notes: 
1. Although the system was produced for the space 
program to monitor the astronauts, it can be modi-
fied for use in hospitals and clinics. The basic 
change requirement is to replace the very expensive 
high-reliability components with economically accept-
able commercial types. 
2. Requests for further information may be directed to: 
Technology Utilization Officer 
Johnson Space Center 
Code JM7 
Houston, Texas 77058 
Reference: TSP73-10401
Patent status: 
NASA has decided not to apply for a patent. 
Source: M. Costello of
Martin Marietta Corp. 
under contract to
Johnson Space Center 
(MSC-14427)
. 
. 
B73-10401	 Category 05,02


Vectorcardiogram

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