Note: Descriptions are shown in the official language in which they were submitted.
1~15783
AA ELC P02 BACK&ROUND OF THE INVENTION
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$72/78 The present invention relates in general to detecting
the shift in the baseline in an electrocardiogram (ECG) and
more particularly concerns a novel system using a multiple
element electrode at a single measuring location with means for
detecting potential differences between elements to reliably
. detect the occurrence of a baseline shift, thereby preventing
automatic monitoring equipment from indicating an alarm condition
about a patient being monitored when an alarm condition should ~
not be indicated. The apparatus is relatively easy to fabricate` -
and install, adds relatively little cost to the system and
operates relatively reIiably with little attention from main-
tenance personnel.
Automatic ECG monitoring systems, whether using simple
rate alarms on a bedside monitor or more complex arrhythmia
; detectors, produce erroneous results at times because of the
~; presence of a non-ECG artifact, consisting of a combination of
~i~ high frequency "muscle noise" and lower frequency "baseline
~ shift". The present invention is concerned with detecting base-
.-~J 20 line shift; that is, a shift in the average value of the ECG
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.;~ signal over a waveform portion.
;,' The usual cause of "baseline shift" is physical mani-
pulation of the electrodes or the skin and muscle underlying
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electrodes which may result from movement of an electrode,
pressing of the surfaces as a result of patient movement, tugging
upon the electrode lead and other causes. Good preparation of
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,!;, the skin surface to which the electrode is attached helps minimize
baseline shift but does not eliminate it. As an example of one
; approach to dealing with this problem reference is made to
~0 U. S. Patent No. 3,905,364 entitled ARTIFACT DETECTOR.
The prior art includes a number of patents on electrodes
~, and multiple electrode systems. In the prior art multiple
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~115783
M ELC P02electrode systems, multiple electrodes or multielement electrodes
~7~778 are used to derive better estimates of the signal or to provid~
flexibility. Some multiple electrode systems are used to `
achieve rapid applications in emergency situations.
Prior art artifact detecting systems exemplified by
Cudahy U. S. Patent No. 3,905,364, Horth U. S. Patent No. 3,552,386
and Vandenberg U. S. Patent No. 3,050,841 detect artifact signals
by sensing changes in the received signal out of range of a
predetermined expected normal ECG from the same pair of electrodes
used to derive the desired ECG signal; that is, between an
electrode at a first ground or common location and an electrode
,, i
; at an ungrounded or uncommon location.
Holsinger U. S. Patent No. 3,868,947 describes a
~; multiple electrode system for artifact compensation and assumes
.
;~, a common mode artifact signal on the center electrodes of
spaced coaxial electrode pairs in contact with the skin at spaced
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` points with the outer annular electrode of each pair connected
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together and to a common ground of a differential amplifier having
a pair of inputs respectively connected to respective ones of
the center electrodes in a pair. This approach is of limited
utility in solving the problem of detecting baseline shift because
, the causes of basline shift at the location of one pair of
electrodes is not likely to produce the same baseline shift, if
any, at a spaced pair of electrodes.
i ~ccordingly, it is an important object of this invention
to provide improved methods and means for detecting baseline shift
' in an ECG signal.
It is a further object of the invention to achieve
the preceding object with apparatus that is relatively easy and
inexpensive to fabricate and install while providing a relatively
; reliable indication of baseline shift with relatively little
attention to the apparatus.
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~:~15783
, .
;~ It is a further object of the invention to achieve
one or more of the preceding objects while providing a useful
; signal.
It is a further object of the invention to achieve
, one or more of the preceding objects useful in automatic ECG
monitoring systems helpful in avoiding erroneous alarm
~i conditions. -
SUMMARY OF 1~ INVENTION
According to the invention, there are first and ~;
1~ second multielement electrode means attached to first and
~' second surface portions of a patient, each electrode means
having elements closely spaced but insulatedly separated,
the ECG potential between the elements being negligible,
there are first and second means for differentially combining,
respectively, the potentials of one element from each of the
multielement electrode means, and the potentials of the other
.,
element from each of the multielement electrode means, to
provide first and second ECG signals, and means for differen-
tially combining the ECG signals to provide an artifact
signal representative of baseline shift.
;" Preferably, the first and second multielement
.:" ,~
electrode means are spaced by a distance greater than that
between the elements of each of the electrode means, the
~ ,.. ; . .
distance between the elements is less than one inch, there
~ are means for combining the ECG signals, and there is a third
;~ electrode means at a third patient surface portion, the
differential combining means having a common input connected
to it. -
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15783
The method of the invention comprises positioning
such multielement electrode portions on first and second :
patient surface portions, combining differentially the ECG
potential of first elements from each multielement electrode
and second the other elements from the multielement
electrodes, to provide first and second ECG signals, and ~-
then differentially combininy the two ECG signals to provide
an artifact signal.
According to a still further broad aspect of the
pre~ent invention there i5 provided an apparatus for provid-
ing an ECG signal and detecting baseline shift in said ECG
signal comprising, a first multielement electrode means :
having elements closely spaced but insulatedly separated for ~:.
connection to a first surface portion of a patientl the ECG
potential between said elements being negligible, a second
multielement electrode means having elements closely spaced
but insulatedly separated for connection to a~:second-surface
portion of said pati~nt, the ECG potential betw~en the
elements of the second electrode means being negligible,
first means for differentially combining the potentials of
one element of said first multielement electrode means and
one element of said second multielement electrode means for
providing a first ECG signal, seco~d means for differentially
combining the potentials of another element of said first
multielement electrode means and another element of said
second multielement electrode means for providing a second
ECG signal, and means for differentially combining said
first and second ECG signals to provide an artifact signal
representative of baseline shift in said ECG signal~
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5783
According to a still further broad aspect of the
present invention there is provided a method of providing
an ECG signal and detecting baseline shift in said ECG
signal comprising the steps of positioning first and second
closely spaced but insulatedly separated electrode portions
in contact with a first surface portion of a patient so that
in the absence of baseline shift the ECG potential there-
between is negligibLe, there being substantially a first
ECG poten~ial on both said electrode po.rtions, positioning
third and fourth closely spaced but insulatedly separated
electrode portions in contact with a second surface portion
of said patient so that in the absence of baseline shift
the ECG potential therebetween is negligible, there being `
substantially a second ECG potential on both said electrode
portions, differentially combining the potential of one of
said first and second electrode portions with the potential
of one of said third and fourth electrode portions to
provide a first ECG signal, differentially combining the
potential of the other of said first and second electrode
portions with the potential of the other of saîd third and -
fourth electrode portions to provide a second ECG signal,
and differentially combining said first and second ECG signals
to provide an art.ifact signal representative of baseline .~:
shift in said ECG signalsO `.
Numerous other features, objects and advantages
will become apparent from the following specification when
read in connection with the accompanying drawing in which: -~
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: ~ ' . ' ` : , ' ~ .,. . " t~ , ,.,, ",~". ., "
~115783
BRIEF DESCRI~?TION OF THE DRAWING
FIG. 1 is a graphical representation of an ECG signal
indicating the occurrence of baseline shift; and
FIG. 2 is a combined block-diagram pictorial repre-
sentation of an exemplary embodiment of a system according to
the invention.
With reference now to the drawing and more particularly
FIG. 1 thereof, there is shown a graphical representation of
an ECG signal with baseline shift occurring in the interval
of the third illustrated beat 11 where the baseline shifts below .
the normal baseline level 12.
Referring to FIG. 2, there is shown a combined
block pictorial representation of a system according to the
. .
invention for detecting baseline shift. The system includes a
.
first ground, common or reference electrode 13 at a first surface
. : . ; .,
location of patient 14 being monitored, a first pair o eLements
15 and 16 of a multielement electrode at a second surface ;~
location of patient 14 and a second pair of elements 17 and 18
of another multielement electrode at a third surface location
of patient 14. The spacing between elements 15 and 16 and
between elements 17 and 18 is significantly less than the
separation between the first location and each of the second and
third locations and preferably that between the second and third
locations. Typical separations between elements 17 and 18 and
between elements 15 and 16 is one inch or less, and they are
pre~erably arranged so that a line connecting their centers is
perpendicular to the electrical axis of the heart. The separation
between elements in a multielement electrode is small enough so
that the ECG potential between them is negligible and large
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~ 57~33
AA ELC P02enough so that the motion of one electrode is at least partially
~/2!78 independent of the motion of the other. The pairs of elements
may be concentric as shown in Holsinger U. S. Patent No. 3,868,947;
however, the connec~ions to extenlal æmplifying apparatus is
different and as described below.
The systems includes a first ECG differential amplifier
21 for providing a first ECG signal on line 22, and a second
ECG differential amplifier 23 for providing a second ECG signal
on line 24. It also includes a differential combiner 25,
.,.
which need not be an amplifier, for providing an artifact signal
on line 26. Differential combiner 25 receives the signals on
lines 22 and 24. ECG utilizing means 27 receives the signals on
,~ lines 22, 24 and 26 and typically provides an alarm signal only
when the ECG signal characterizes an unstable condition of
,~ patient 14, such as arrhythmia or an unacceptable heartbeat rate, `
~i,
while preventing the occurrence of an alarm signal when an
artifact signal on line 26 occurs,- signifying that a condition
has occurred at an associated pair of elements producing a
baseline shift.
The grounded, common or reference input C of each
differential amplifier 21 and 23 is connected to reference
,
~; electrode 13 at the first patient surface location. It is common
-~, practice to have a reference terminal such as 13 attached to the
patient and connected to one or more common terminals of the
;~ amplifying means for reducing noise. The 1 and 2 signal inputs
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of first ECG differential amplifier 21 are connected to
~ electrode elements 17 and 15, respectively, the elements being
;' selected from different multielement electrodes at different
. .
` patient locations. The 1 and 2 signal inputs of the second ECG
differential amplifier 23 are connected to the other elements
- 18 and 16, respectively, of the different multielement electrodes.
Accordingly, two nearly identical ECG signals 22 and
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1115783
24 from two multielement electrodes are produced. The difference
between these two parallel ECG signals, as detected by differen-
tial combiner 25, is baseline shift, creating artifact signal
26.
The specific means for utilizing the ECG signals 22
and 24 and the artifact signal 26 is not a part of the invention.
For example, it is possible to use either of the ECG signals
22 and 24 or to combine the two by summation to produce the true
ECG. Or ECG utilizing means 27 may include, in addition,
circuitry that responds to the occurrence of an artifact signal ' '
on line 26 for providing a signal that inhibits the alarm
indicating circuitry. The ECG utilizing means might also or
alternatively include circuitry for combining the artifac~ signal
with the ECG signal to effectively restore the shifted baseline
substantially to the normal baseline 12.
There has been described novel apparatus and tech-
niques for detecting a baseline shift in an ECG signal. ,It is `i
evident that those skilled in the art may now make numerous
modifications and uses of and departures from the specific embodi-
2~ ment described herein without departing from the inventive con-
cepts. Consequently, the invention is to be construed as
embracing each and every noveL feature and novel combination of
features present in or possessed by the apparatus and techniques
herein disclosed'and limited solely by the spirit and scope of
the appended claims.
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