U.S. patent number 3,868,947 [Application Number 05/406,870] was granted by the patent office on 1975-03-04 for concentric electrode construction for an electrocardiogram transmitter.
This patent grant is currently assigned to The United States of America as represented by the Secretary for. Invention is credited to William P. Holsinger.
United States Patent |
3,868,947 |
Holsinger |
March 4, 1975 |
Concentric electrode construction for an electrocardiogram
transmitter
Abstract
An electrode assembly for generating electrocardiogram
bioelectric potential signals suitable for wave-form analysis is
disclosed. The electrode assembly comprises two separate
transmitter electrodes adapted to be placed on the skin of a
subject. Each electrode includes a central conducting surface and
an outer conducting surface disposed in surrounding relationship
about the periphery of the central conducting surface, the outer
conducting surface being spaced from the central conducting surface
by an intermediate insulating barrier region. The outer conducting
surfaces of each electrode are connected in common and to a common
ground of a differential amplifier. The central conducting surface
of each of the electrodes is connected to a different respective
input of the differential amplifier whereby a signal representative
of the bioelectric potential is provided at the differential
amplifier output.
Inventors: |
Holsinger; William P. (Herndon,
VA) |
Assignee: |
The United States of America as
represented by the Secretary for (Washington, DC)
|
Family
ID: |
23609731 |
Appl.
No.: |
05/406,870 |
Filed: |
October 16, 1973 |
Current U.S.
Class: |
600/382 |
Current CPC
Class: |
A61B
5/30 (20210101) |
Current International
Class: |
A61B
5/04 (20060101); A61b 005/04 () |
Field of
Search: |
;128/2.6E,2.1E,DIG.4,2.6B,2.6R,404,410,411,416,418 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Lagow et al., "Anodic Insul. Tant. Oxide ECG Elecs.," IEEE Trans.
on Bio-Med. Engr'g., Vol. 18, No. 2, March, 1971, pp.
162-164..
|
Primary Examiner: Gaudet; Richard A.
Assistant Examiner: Cohen; Lee S.
Claims
What is claimed is:
1. An electrode assembly for generating electrocardiogram
bioelectric potential signals suitable for wave-form analysis, said
assembly comprising: two separate transmitter electrodes adapted to
be placed on a subject's skin in electrical contact therewith, each
electrode comprising a flat exposed disc which includes an
electrically conductive central disc member and an outer conducting
ring disposed in surrounding relationship about the periphery of
said central conductive member, said outer conducting ring being
spaced from said central conductive member by an intermediate
insulating annulus, said central conductive member, said outer
conducting ring, and said insulating annulus being coplanar and
concentrically disposed; means for electrically coupling said outer
conducting rings of each said electrode in common and to a common
ground of a differential amplifier; and means for electrically
connecting said central conductive member of each said electrode to
a different respective input of the differential amplifier, whereby
a signal representative of the bioelectric potential is produced at
the differential amplifier output.
2. An electrode assembly as defined in claim 1, wherein said
central conductive disc and said outer conducting ring are
constructed of stainless steel, and wherein said insulating annulus
is of epoxy.
Description
BACKGROUND OF THE INVENTION
This invention generally relates to electrocardiogram techniques,
and particularly concerns a novel transmitting electrode assembly
therefor by which bioelectric potential signals are generated of a
quality suitable for wave-form analysis.
With particular reference initially being directed to FIG. 1 of the
appended drawings, a conventional prior art technique and apparatus
is shown by which bioelectric potential signals are typically
generated in the art, such signals being utilized to drive a chart
recorder of an electrocardiogram monitoring machine. Since a
complete electrocardiogram diagnosis of heart disorders requires an
analysis of the bioelectric potential waveform, three separate
surface electrodes are normally provided, such as electrodes 10,
12, and 14, each of these electrodes being disposed on the skin of
a patient. Electrode 14 is conventionally coupled to the common
ground 16 of a differential amplifier 18, whereas electrodes 10 and
12 are conventionally coupled to different respective inputs 20 and
22 of differential amplifier 18. Three separate signals are
therefore generated, with the output from the differential
amplifier 18 as represented by reference numeral 24 being the
bioelectric potential difference between electrodes 10 and 12 from
the ground defined by the potential of electrode 14.
Difficulties are encountered with the conventional prior art
apparatus as shown in FIG. 1, particularly as concerns obtaining
clinical quality electrocardiogram tracings due to the large amount
of filtering which would be necessary to eliminate ambient noise
from two floating sources represented by electrodes 10 and 12.
Further, the three-electrode construction of the prior art is quite
inconvenient to use since it is necessary to firmly attach the
electrodes to the patient's skin, it not being possible for the
user of the apparatus to simply hold one electrode in each hand so
as to obtain a proper monitoring.
SUMMARY OF THE INVENTION
It is thus apparent that a need exists in this art for an improved
electrode assembly of simple construction which is capable of
providing clinical grade electrocardiogram signals. It is the
primary objective of the instant invention to provide such an
improved electrode assembly.
A further objective of the instant invention is the provision of an
electrode assembly which does not require three separate surface
contacting regions but, instead, produces a high quality
bioelectric potential signal from only two surface contacts, thus
markedly increasing the convenience to the user thereof.
These objectives, as well as others which will become apparent as
the description proceeds, are implemented by the instant inventive
electrode assembly which, in its preferred embodiment, constitutes
two separate transmitter electrodes adapted to be placed on a
subject's skin. Each electrode includes a central conducting
surface and an outer conducting surface which is disposed in
surrounding relationship about the periphery of the central
conducting surface but is spaced therefrom by an intermediate
insulating barrier region. The outer conducting surfaces of each
electrode are electrically coupled in common to one another and to
a common ground of a differential amplifier. The central conducting
surface of each of the electrodes are electrically connected to a
different respective input of the differential amplifier. As a
result, a signal representative of the bioelectric potential is
provided at the differential amplifier output, which signal is of
high quality and is suitable for complete wave-form analysis.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood, and further features and
advantages thereof will become apparent from the following detailed
description of a preferred inventive embodiment, such description
making reference to the appended sheet of drawings, wherein:
FIG. 1 is a schematic illustration of a prior art electrode
transmitter for an electrocardiogram machine;
FIG. 2 is a schematic illustration of the electrode assembly
constructed in accordance with the teachings of the instant
invention; and
FIG. 3 is an electrical schematic diagram depicting an equivalent
circuit of the construction of the instant invention depicted in
FIG. 2, for purposes of better explaining the electrical operation
of the invention.
DETAILED DESCRIPTION OF A PREFERRED INVENTIVE EMBODIMENT
With specific reference now to FIG. 2 of the application drawings,
the construction of the instant inventive electrode assembly will
be described. Two electrodes are provided, generally designated by
reference numerals 26 and 28, each electrode being contemplated to
be disposed over and in contact with the underlying skin of a
subject as is shown. Each electrode incorporates three separate and
distinct portions.
A central conducting surface or disc 30, preferably constructed of
stainless steel, is provided for each of the electrodes. An outer
conductive surface or ring 32, also preferably constructed of
stainless steel, is disposed in surrounding relationship about the
periphery of the central conducting surface or disc 30 but is
spaced apart therefrom by an intermediate insulating barrier region
34. The barrier region 34 preferably constitutes an epoxy annulus
which provides electrical insulation as well as a structural
barrier.
The outer conductive ring 32 of each of the electrodes 26 and 28 is
electrically connected in common together via conductor 36 and is
further connected to the common ground 16 of differential amplifier
18. The central conducting portions or discs 30 of each of the two
electrodes are connected to the respective different inputs 20 and
22 of differential amplifier 18, as is shown. The separate parts or
regions of each electrode 26 and 28 are accordingly disposed in a
concentric relationship with one another.
In use, the outer conductive surface or ring 32 of each electrode
26 and 28 provides shielding as well as the important ground
reference. The palm of the user's hand, or the heel of the hand,
when placed on each electrode 26 and 28, will straddle the epoxy
insulating annulus 34 so that coupling occurs to both conductors 30
and 32. In this fashion, the body and the electronics will assume
the same potential and any differences between electrode leads is
cancelled in so-called "common-mode," as is typical. Further, since
both outer rings of the electrodes are connected together in
electrical common, good contact is assured with either hand of the
user for establishing a ground reference.
To analyze the electrical operation of the inventive electrode
assembly of FIG. 2, attention is directed to FIG. 3 of the
application drawings wherein an equivalent circuit of the electrode
assembly is shown. Similar reference letters have been provided on
both FIG. 2 and FIG. 3 of the application drawings so as to
establish a frame of reference. In this respect, it should be
appreciated that the voltage potential E.sub.1 is the
electrocardiogram bioelectric potential having a typical magnitude
of 1 millivolt. The voltage designated by reference E.sub.2 is the
potential difference within the internal conductive tissue between
the regions of the electrode ring and disc and is less than 1
microvolt. Accordingly, E.sub.2 for the purposes of the following
calculations can be considered to constitute zero.
Z.sub.in is the input impedance of the amplifier, Z.sub.T is tissue
impedance, and Z.sub.S is skin-to-electrode impedance. Relative
magnitudes among these parameters is expressed by
Z.sub.in >> Z.sub.S >> Z.sub.T
For path AC
V.sub.AC .apprxeq. (E1/2) since Z.sub.S >> Z.sub.T
remembering that E.sub.2 = 0
V .sub.DC .apprxeq. V.sub.AC since Z.sub.in >> Z.sub.S +
Z.sub.T
therefore
V.sub.DC .apprxeq. (E1/2)
A similar argument prevails for V.sub.BC and V.sub.EC
so
V.sub.EC .apprxeq. (-E1/2)
The differential amplifier of gain .alpha. subtracts the two phases
giving an effective output of .vertline. .alpha. E.sub.1
.vertline.. (Common-mode voltages are cancelled.)
Consider also the case if one electrode does not have the ground
path connected. (i.e., Absence of a ground ring or one hand is not
making contact with the ring.)
For AC open
V.sub.AC .apprxeq. E.sub.1 since Z.sub.IN >> Z.sub.S +
Z.sub.T and V.sub.DC .apprxeq. V.sub.AC for the same reason.
Therefore
V.sub.DC .apprxeq. E.sub.1
For the other leg V.sub.EC .apprxeq. V.sub.BC .apprxeq. 0 because
Z.sub.in >> Z.sub.S
These two signals, when combined by the differential amplifier of
gain .alpha., also yield an output of .vertline. .alpha. E.sub.1
.vertline..
It should thus be appreciated that the objects initially set forth
at the outset of the specification have been successfully achieved,
use of the electrode of the instant invention finally enabling the
transmission of clinical-grade electrocardiograms from even
battery-powered devices with economic advantages necessary for mass
screening of the public. Moreover, while there has been shown and
described a present preferred embodiment of the invention, it is to
be distinctly understood that the invention is not limited thereto,
but may be otherwise variously embodied and practiced within the
scope of the following claims.
* * * * *