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FIELD OF THE INVENTION
This invention relates to sensing of the condition and activity of the
heart by measuring electrocardiographic data. In particular, this
invention relates to a new and improved method of gathering
electrocardiographic data and to a system for collecting such data and
transmitting the collected data to a remote location for analysis.
BACKGROUND OF THE INVENTION
Since the time it was discovered that the pumping heart was central to
maintaining life, medical science has developed new and improved ways to
monitor cardiac function and to diagnose cardiac dysfunction. Currently,
the electrocardiograph or "EKG" (alternatively, "ECG")is considered the
best method for monitoring cardiac function.
The electrocardiograph instrument monitors cardiac function by recording
changes in electrical potential detected by electrodes attached at various
locations on the monitored patient's skin. The electrodes measure
fluctuations in electric potential caused by depolarization and
repolarization of the cardiac muscle during each heartbeat. The EKG
instrument translates the fluctuations in electric potential at various
locations into a set of traces on an electronic screen or paper "rhythm
strip" chart, producing the familiar spiked beat pattern. The magnitude
and timing of various fluctuations as represented by a trace or rhythm
strip are then analyzed to provide information relating to heart rate,
coordination between the various chambers of the heart, condition of the
heart tissue and cardiac dysfunction.
An individual trace or rhythm strip is a representation of data collected
from one electrode "lead". A "lead" is a combination of two electrodes
which produces an electropotential "picture" of the heart from a given
angle. Though electrodes can be placed at many different locations on a
patient's skin, the placement of electrodes at ten specific locations on
the patient's skin have been set by convention. The ten standard electrode
locations produce a total of twelve different "conventional leads."
Many EKG instruments monitor all twelve conventional leads, providing very
detailed and comprehensive data concerning cardiac function. Some
instruments can selectively monitor and record a collection of three, four
or six leads selected by the user. Other instruments monitor all twelve
leads simultaneously and display three, four, six or twelve traces at a
time and incorporate the ability to display different lead configurations
during an EKG examination. All of these systems produce traces on a
monitor or a rhythm strip as the data is collected.
Unfortunately, obtaining a complete conventional twelve-lead diagnosis
requires (1) an instrument which is usually both expensive and, as a
result of its size, difficult to transport easily; (2) the presence of a
physician or EKG technician at the site where the data is collected; and
(3) an examination which is invasive for the patient since the patient
must be disrobed above the waist and, in some cases, shaved so that
certain of the electrodes can be attached to the chest. While monitoring a
subset of the twelve lead system alone may provide sufficient data to
recognize many features of cardiac function and dysfunction, one-lead and
two-lead systems may not allow a physician or EKG technician to
differentiate particular arrythmic conduction disturbances or ischemic
events.
In many situations, including home-based post-operative care, patient
screening and outpatient surgical procedures, it is desirable to monitor
cardiac activity and to detect irregularities therein without making the
complete diagnosis provided by a conventional twelve lead EKG instrument.
For example, during many dental and oral surgery procedures the patient is
exposed to extreme physiological stress which can result in cardiac
dysfunction or arrest. By monitoring the patient's cardiac function before
treatment, during treatment and/or when signs of extreme stress (heavy
breathing, accelerated pulse) are observed the quality of patient care is
increased and a cardiac event may be averted.
Although non-cardiology professionals, including dentists and outpatient
surgeons, are interested in monitoring the heart function of their
patients before, during and after stressful procedures, they seldom use
EKG technology because of the sizeable cost of EKG instruments and because
of their lack of expertise in reading EKG data. Consultation with a
cardiologist or EKG technician is usually necessary to translate the EKG
data into information useful to the treating professional. Few
non-cardiology professionals have such resources readily available and, as
a result, the effects of stressful procedures upon patient cardiac
function are often not monitored. Even when non-cardiology professionals
have sought the counsel of cardiologists, e.g., in extreme emergency
situations during a procedure, the cardiologist is greatly hindered by the
inability to examine any EKG data. Unless the cardiologist is present with
the patient, it is often impossible to make a useful determination of the
patient's condition without an EKG trace.
It would, therefore, be desirable to provide a simple, economical and
non-invasive method and system to collect a clinically significant sample
of electrocardiographic data. Preferably, such data should be collected in
a manner such that it can be easily communicated to a cardiologist or EKG
technician for interpretation.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method of gathering
electrocardiographic data is disclosed wherein the EKG data is collected
by sequentially monitoring the difference in electrical potential measured
at each of at least three patient leads for a time period greater than 15
seconds, preferably for equal time periods of 20 seconds each. Although
more than three leads and longer monitoring time periods may be used, a
60-second three-lead EKG data sample is, as set forth below, clinically
sufficient to monitor cardiac function and to diagnose most cardiac
dysfunctions.
A system for collecting such electrocardiographic data is also disclosed.
The system allows the collected data to be stored for later translation
and interpretation. The stored data may also be communicated over phone
lines for translation and interpretation at a remote site by trained
individuals.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a schematic representation of the use of the method and system of
the present invention.
FIG. 2 is a pictorial representation of a conventional EKG electrode as
used in the present invention.
FIG. 3 is a schematic representation of Einthoven's triangle and the
location of the electrodes forming the Standard Limb Leads.
FIG. 4 is a schematic representation of the orientation and polarity of the
Standard Limb Leads.
FIG. 5 is a representation of typical EKG traces from each of the Standard
Limb Leads as they would appear on a typical EKG instrument.
FIG. 6 is a representation of the same EKG trace from each of the Standard
Limb Leads as collected by the method and system of the present invention.
FIG. 7 is a switching diagram showing the pattern of switching between the
Standard Limb Leads, in the device employed in the preferred embodiment of
the present invention, in relation to the EKG trace depicted in FIG. 6.
FIG. 8 is a pictorial view of the preferred embodiment of the system of the
present invention.
FIG. 9 is a block diagram of the EKG apparatus in accordance with the
preferred embodiment of the present invention.
FIGS. 10, 10a-c and 11, 11a-c are electrical schematics of the preferred
embodiment of the present invention as summarized in FIG. 9.
DETAILED DESCRIPTION OF THE INVENTION
The preferred embodiment of the method of the present invention generates a
sample of patient EKG data comprising three equal segments of data from
each of three pairs of electrodes attached to the patient's body, each
data segment being about 20 seconds long.
To monitor cardiac function using the conventional lead system, electrodes
are placed on each wrist, each ankle and at six locations on the chest.
Each pair of electrodes or "lead" measures depolarization and
repolarization of the cardiac muscle along a different plane by measuring
the fluctuation in electrical potential between the two electrodes. In
effect, the twelve conventional leads allow twelve potentiometric
"pictures" to be taken of the heart from twelve different directions, thus
providing the physician or EKG technician with a more detailed description
of cardiac function. The twelve conventional leads are usually divided
into three groups of leads: the Standard Limb Leads, the aVR/aVL/aVF group
and the V1-V6 group. The aVR/aVL/aVF group forms leads from electrodes
attached to the arms and legs. The V1-V6 group forms leads by pairing
electrodes placed on the chest with an electrode on the patient's back,
which acts as an "effective" negative electrode. Information regarding the
various lead systems and their relation to cardiac function and EKG output
can be found, for example, in Dubin, D., "Rapid Interpretation of EKG's,"
3 d ed. (COVER Publishing, Tampa, Fla. 1981).
The Standard Limb Lead system can be traced to the original
electrocardiographic lead system devised by Willem Einthoven (1860-1927).
In his lead system the vector representing the direction and magnitude of
the wave of cardiac depolarization was located in the center of a triangle
formed by the left and right shoulders and the groin ("Einthoven's
triangle"). For convenience the electrodes 1, 2 and 3 in the Standard Limb
Lead system are connected to the right and left forearms or wrists and the
left leg, each of which is considered an extension of the right shoulder,
left shoulder and groin, respectively, as shown in FIG. 3. By convention,
the Standard Limb Leads are connected to an EKG apparatus such that "Lead
I" records the potential difference between the right arm and the left
arm, with the left arm electrode being positive. "Lead II" records the
potential difference between the right arm and the left leg, with the left
leg electrode being positive. "Lead III" records the potential difference
between the left arm and the left leg, with the left leg electrode being
positive. FIG. 4 summarizes the orientation and polarity of the Standard
Limb Leads.
In the preferred embodiment of the method of the present invention cardiac
function is monitored using the Standard Limb Leads as shown in FIG. 3. In
contrast to conventional measurements made using the Standard Limb Leads,
the method of the present invention monitors cardiac function in a unique
manner such that data is collected by measuring potential difference at
Lead I for 20 seconds, then measuring potential difference at Lead II for
20 seconds, and finally measuring potential difference at Lead III for 20
seconds. FIGS. 5 and 6 depict two different forms of traces produced by
monitoring these leads. FIG. 5 shows approximately 60 seconds of EKG data
from an EKG instrument that read 20 seconds of data from all three leads
simultaneously, with each lead displayed in parallel. FIG. 6 shows a trace
or "rhythm strip" of the same cardiac activity depicted in FIG. 5 that was
produced by the method of the present invention. A 20 second sample from a
trace from Lead I 4 is followed by 20 seconds of trace from Lead II 5, and
finally by 20 seconds of trace from Lead III 6.
Collecting 60 seconds of EKG data generated by three leads is normally
adequate to adequately detect most cardiac rhythm anomalies, as most
irregular rhythms will manifest themselves within the one-minute minimum
monitoring period. A collection of data substantially less than one minute
long may not represent enough EKG data to show even frequent arrythmias.
The method of generating EKG data from three different leads for a total
of 60 seconds normally provides sufficient data to detect rate and most
rate anomalies (including ectopic pacemakers, sinus tachycardia, and sinus
bradycardia), rhythm and most rhythm anomalies (including arrythymia,
wandering pacemakers, fibrillations, premature beats, escape beats,
arrest, heart blocks, paroxysmal tachycardia and flutter), axis and most
axial anomalies, hypertrophy and infarctions. A three-lead system can also
eliminate many instances of "invisible" symptoms found in systems using
fewer leads. One-lead and two-lead monitoring are usually inadequate to
differentiate particular arrythmic conduction disturbances or ischemic
events that may not be visible on certain leads. For example, right bundle
branch block can be seen on Lead II, but is not visible on Leads I and
III. Three-lead monitoring also decreases the likelihood that the data
will be useless because of artificial signals ("artifacts") in the trace,
which are usually only seen in one (but not more than two) leads.
The preferred method of the present invention allows cardiac function to be
monitored by three different leads over the course of a minimum required
period of 60 seconds without requiring simultaneous monitoring or storing
of signals from multiple leads. The method produces a smaller volume of
data, which can be processed and analyzed more efficiently and
economically without losing diagnostic certainty. Arrythmias or irregular
beats show up during the tripartite monitoring period regardless of the
lead being monitored. Irregularities in individual beats or beat patterns
are detected by showing data from all three leads. Moreover, the decrease
in the volume of data necessary to produce a clinically relevant analysis
makes it easier to communicate the collected data to trained professionals
for interpretation. The method of the present invention also requires less
electronic memory to hold the resulting collection of EKG data. To produce
a rhythm strip like that of the present invention a conventional
twelve-lead EKG instrument would have to store twelve minutes of data
(i.e., one minute from each lead). The present invention is more efficient
in that it only requires storage of one minute of data (i.e., 20 seconds
from each lead).
In alternative embodiments of the present invention, each lead could be
monitored for more or less than 20 seconds. Although 10 seconds seems to
be a minimum for obtaining a useful sample of data, some conditions may
not manifest themselves in 30 seconds of trace. Monitoring periods longer
than 20 seconds may, therefore, be used, but they negate in part the
economic and efficiency advantages of collecting the necessary data in one
minute.
Leads other than the Standard Limb Leads may also be used in the method of
the present invention. The aVR/aVL/aVF lead group would be most
appropriate. The V1 through V6 leads could also be used, although the
method would then become more invasive in that the patient would have to
be exposed above the waist, and shaved in some cases, for connection of
the electrodes. Use of the Standard Limb Leads or the aVR/aVL/aVF lead
group makes the method non-invasive since the electrodes can be
conveniently attached to the patient's wrists and ankles.
In the preferred embodiment of a system for collecting EKG data according
to the above-described method, standard EKG electrodes 1, 2 and 3
(commercially available from Andovar Medical, Haverhill, Mass.) are
adhered to the palm side of each wrist and the inside of the left leg of
the patient as shown in FIGS. 1, 2 and 3. Each electrode is comprised of
an adhesive conductive tab 80 which is adhered to the patient's skin 81
and connected to a shielded cable 83 by a clip 82 (FIG. 2). The electrodes
are connected to the apparatus 10 as shown in FIG. 1.
As shown in FIG. 1, when the collected electrocardiographic data is
transmitted from apparatus 10 via telephone lines 72 to a remote receiver
70, the method and system of the present invention produce a paper chart
or "rhythm strip" 71. The preferred embodiment of the rhythm strip, shown
in FIG. 6, comprises a single 60-second trace which is made up of three
sequential serial 20-second traces from Lead I, Lead II and Lead III,
respectively. Alternative embodiments of the rhythm strip will vary in
overall duration of the single trace and the duration of each sequential
serial trace from each lead.
The apparatus of the present invention will next be described in detail.
Referring to FIGS. 8 through 11, an apparatus 10 for monitoring, recording
and transmitting EKG data in accordance with the present invention broadly
includes an input buffer 12, switching network 14, comparator 16, A/D
convertor 18, storage means 20, D/A convertor 22 and transmitter circuit
24. Standard electrodes 1, 2 and 3 are attached to the patient at various
locations as previously described. The various operating modes of
apparatus 10 are controlled by switches 26, 27 and 28. The EKG data
collected by apparatus 10 may be transmitted over a standard telephone
line 72 to a receiver 70 for analysis at a remote location or may be
displayed locally on an EKG strip chart printer (not shown). A
single-channel receiver in common use for accepting pacemaker data (e.g.,
Teletrace.RTM. Telephone EKG Receiver, Model 9410, commercially available
from Medtronic, Inc., Minneapolis, Minn.). Other currently-available
single-channel receivers, which are for the most part used to receive data
transmissions from pacemaker monitoring devices, may also be used. By
having the apparatus 10 send to a widely-used type of receiver, persons
using the method and system of the instant invention can send data to
almost any cardiology office with nothing more than the apparatus 10 and a
telephone 73. This arrangement makes the method and system both convenient
and economical, because the advice of a cardiology professional can be
sought without using additional or expensive EKG or receiving
instrumentation and by only requiring the attention of the cardiologist
when data is periodically transmitted and received.
Referring now to FIGS. 8 and 9, the functional operation of apparatus 10 in
accordance with the present invention will be described. Three electrodes
1, 2 and 3 are attached to the patient as previously described. Each of
the electrodes 1, 2 and 3 are connected through shielded cables 7, 8 and 9
to input terminals 30, 32 and 34, respectively. Input buffer 12 receives
and amplifies the analog input signals present on electrodes 1, 2 and 3.
Once amplified, analog signals 36, 38 and 40, corresponding to the output
of input terminals 30, 32 and 34, respectively, are presented to switching
network 14 for selecting the desired pair of signals to be sensed.
For the Standard Limb Lead configuration, electrode 1 is attached to the
patient's right arm; electrode 2 is attached to the patient's left arm;
and electrode 3 is attached to the patient's left leg as previously
described. For convenience and to insure that correct reading is obtained,
each electrode and its corresponding input terminal are color-coded
(electrode 1 and input terminal 30--white; electrode 2 and input terminal
32--black; and electrode 3 and input terminal 34--red). Switch 26 may be
selectively positioned at any one of the four positions 42, 44, 46 and 48
to read continuously from Lead I, Lead II, Lead III or to automatically
read sequentially from all three leads.
Apparatus 10 may be set to continuously present Lead I, Lead II or Lead III
voltage to comparator 16 by setting switch 26 at positions 42, 44 or 46,
respectively. As explained earlier, each lead must represent a pair of
electrodes; Lead I (V.sub.2 - V.sub.1), Lead II (V.sub.3 - V.sub.1), Lead
III (V.sub.3 - V.sub.2). By setting switch 26 to position 42, switching
network 14 will continuously present analog signal 30 (electrode 1) at
negative input 52 and analog signal 32 (electrode 2) at positive input 50,
thus reading Lead I. With switch 26 at position 44, switching network 14
will continuously present analog signal 30 (electrode 1) at negative input
52 and analog signal 34 (electrode 3) at positive input 50, thus reading
Lead II. With switch 26 at position 46, switching network 14 will
continuously present analog signal 32 (electrode 2) at negative input 52
and analog signal 34 (electrode 3) at positive input 50, thus reading Lead
III. It will be clear to those skilled in the art that any combination of
input signals can be presented together on positive signal 50 and negative
signal 52 by changing the position of electrodes 1, 2 and 3 on the
patient's body, or by changing the order in which electrodes 1, 2 and 3
are connected to input terminals 30, 32 and 34.
Apparatus 10 also be set to sequentially monitor Leads I, II and III in
accordance with the method of the present invention described previously.
When switch 26 is in position 48, an internal timing circuit 145 (FIG. 10)
is enabled which controls the length of time each lead is monitored and
also controls sequencing through each lead. The pre-selected time interval
is controlled by the clock frequency selected from clock 145 and is
enabled by switch 27. When the time interval is completed, switching
network 14 changes the combination of analog signals presented together at
positive input 50 and negative input 52 to the next combination. Timing
circuit 146 is also connected to start switch 27 to disable the storage
and/or transmission of the EKG data after completion of one sequential
cycle of the three leads. For the reasons set forth above, it is preferred
that the pre-selected time interval be at least 20 seconds. To standardize
interpretation of EKG data being transmitted, the time interval is
normally set at 20 seconds by choosing biasing components for clock 145
such that a frequency of 100 Hz is presented to timing circuit 146.
Comparator 16 receives the particular combination presented at positive
input 50 and negative input 52 and feeds A/D convertor 18 a reference
voltage signal 54 (1.5 volts) and analog data signal 56 for conversion.
A/D convertor 18 performs an 8 bit wide conversion on analog signal 56,
sampling the signal at a sampling frequency of 250 Hz. Eight bit wide data
bus 58 is connected to the output of A/D convertor 18 and to the input of
D/A convertor 22. Data bus 58 is also connected to memory 20. By setting
switch 28 at position 29 (Record), memory 20 is enabled to receive digital
data from A/D convertor 18 via data bus 58 to be sequentially stored. When
switch 28 is set at position 31 (Transmit), memory 20 retrieves the stored
data and transfers it via data bus 58 to D/A convertor 22. When (i) switch
28 is set at position 31 (Transmit), (ii) switch 26 is in position 42, 44
or 46, and (iii) switch 27 is not enabled, the apparatus will continuously
transmit data from the set of electrodes corresponding to the set position
of switch 26.
Transmission circuit 24 receives the reconverted analog signal 60 from D/A
convertor 22 which represents the particular combination of analog data
signals as compared to the 1.5 volt reference voltage signal by comparator
16. Reconverted analog signal 60 is placed on a carrier frequency and
converted into an audio signal 62 which is output through speaker 74. A
typical acoustical coupler 75 receives the handset of telephone 73,
thereby allowing the audio signal 62 to be sent out over the telephone
lines 72 for remote analysis. In an alternative embodiment, audio signal
62 is received by a local EKG strip chart printer to allow the EKG data to
be viewed locally.
Referring to FIGS. 10 and 11, the circuitry of apparatus 10 in accordance
with the preferred embodiment of the present invention is described in
detail below.
Input buffer 12 comprises three operational amplifiers 100, 102 and 104 of
a quad operational amplifier TL064ACN semiconductor chip (commercially
available from Texas Instruments). Input terminal 30 connects to
operational amplifier 100 through resistor 106, diodes 108 and 110 and
capacitor 112. Input terminal 31 connects to operational amplifier 102
through resistor 114, diodes 116 and 118 and capacitor 120. Input terminal
32 connects to operational amplifier 104 through resistor 120, diodes 122
and 124 and capacitor 126.
The switching network 14 comprises a three-to-eight line decoder 128 (a
74HC138 semiconductor chip), three AND gates 130, 132 and 134 of a quad 2
input 74HC08 semiconductor chip AND gate, four NAND 136, 138, 140 and 142
of a quad 2 input 74HC00 semiconductor chip NAND gate, a multiplexer 144
(a DG212J semiconductor chip), a 14-stage ripple carry binary counter 145
(a 4060 semiconductor chip) and a D flip-flop with preset and clear 146 of
a 74HC74 semiconductor (all commercially available from National
Semiconductor). Selector switch 26 with four positions 42, 44, 46 and 48
selectively connects one input of AND gates 130, 132 and 134 to ground.
When not grounded, each such input is connected to a 5-volt power supply
through 10K ohm resistors 150, 152 and 154 in a pre-selected manner. The
output of AND gates 130, 132 and 134 connect to multiplexer 144 through
NAND gates 136, 138, 140 and 142. When switch 26 is in the "auto" position
48, counter 145 actuates decoder 128 connected to AND gates 130, 132 and
134. A normally open push button switch 27 and a 10K ohm resistor 158 is
connected to the CLR input of flip-flop 146, while AND gate 160 and
invertor 162 are connected at the RESET input. Together these components
form a starting trigger.
Comparator 16 comprises operational amplifiers 164, 166, 168 and 170 of a
quad op amp TL064ACN semiconductor chip (commercially available from Texas
Instruments). Operational amplifier 164 is connected to multiplexer 144
and forms a differential amplifier in conjunction with 1M ohm resistors
172 and 174, 200K ohm resistors 176 and 178 and 1-microfarad blocking
capacitors 180 and 182. Operational amplifier 166 provides a 1.5 volt
reference signal using the biasing provided by 10K ohm resistor 184, 40.2K
ohm resistor 186, 60.4K ohm resistor 188, zener diode 190, capacitors 192
and 194. Operational amplifier 168 comprises a 60 Hz q=4 notch filter in
conjunction with resistors 196, 198, 200, 202 and 204 and capacitors 206,
208 and 210 and receives the output of the differential amplifier 164.
Operational amplifier 170 forms a high gain amplifier in conjunction with
resistors 212, 214, and 216 and capacitor 220 and receives as one input
the output of the 60 Hz notch filter.
The A/D convertor 18 comprises an ADC0804 semiconductor chip 221 and
connects to comparator 16 through resistor 218. The ADC0804 semiconductor
chip 221 is selectively set by the use of resistors 222, 224 and 226 and
capacitors 228, 230 and 232, invertors 234 and diode 240 and drives OR
gate 238 and record indicator light-emitting diode 242.
Memory means 20 connects to the A/D convertor 18 and comprises a static RAM
244 (commercially available from Hitachi Semiconductor, part No.
HM62256LP-15), two 12-stage ripple carry binary counters 246 and 248
(commercially available from National Semiconductor, part No. CD4040),
invertors 250, 252 and 254 of a 74HC04 hex invertor and an OR gate 256.
Invertors 252 and 254 in conjunction with resistors 258 and 260 and
capacitor 262 form a 450 Hz oscillator.
The D/A convertor 22 is connected to the A/D convertor 18 and the storage
means 20 and includes a D/A convertor semiconductor chip 264 (commercially
available from Analog Devices, Norwood, Mass.) and a filter 266. Filter
266 comprises operational amplifier 267 of a quad op amp TL064ACN,
resistors 268, 270, 272 and 274 and capacitors 276 and 278. Filter 266 has
a passband gain of two.
The transmission circuit 24 is connected to the D/A convertor 22 and
includes VCO circuit 280, flip-flop circuit 282, operational amplifier
circuit 284 and switch circuit 286. The switch assembly 286 includes a
switch 28, an OR gate 288, resistors 290 and 292 and a transmit indicator
light-emitting diode 294. The VCO circuit 280 connects to the D/A
convertor 22 and comprises a VCO semiconductor chip 296 (commercially
available from National Semiconductor, part No. LM331) and includes
resistors 298, 300, 302, 304, 306, 308, 310 and 312 and capacitors 314,
316 and 318. The flip-flop circuit 282 connects to the VCO assembly 280
and comprises a 74HC74 dual flip-flop with a reset and clear 320 and
includes resistors 322, 324 and 326 and capacitors 328 and 330. The
operational amplifier circuit 284 connects to the flip-flop assembly 282
and comprises an operational amplifier 322 of a quad op amp TL064ACN and
includes resistors 334 and 336 and capacitors 338, 340 and 342.
From the foregoing, it will be obvious to those skilled in the art that
various modifications in the above-described methods can be made without
departing from the spirit and scope of the invention. Accordingly, the
invention may be embodied in other specific forms without departing from
the spirit or essential characteristics thereof. Present embodiments,
therefore, are to be considered in all respects as illustrative and not
restrictive, the scope of the invention being indicated by the appended
claims rather than by the foregoing description, and all changes which
come within the meaning and range of equivalency of the claims are
therefore intended to be embraced therein.
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