United States Patent [19]
`Dougherty et al.
`
`[11] Patent Number:
`[45]. Date of Patent:
`
`5,027,824
`Jul. 2, 1991
`
`[54]
`
`METHOD AND APPARATUS FOR
`DETECTING, ANALYZING AND
`RECORDING CARDIAC RHYTHM
`DISTURBANCES
`
`[76]
`
`Inventors: Edmond Dougherty, 523 W. Valley
`Rd., Strafford, Pa. 19087; George
`Simmons, 1821 Sycamore St.,
`Haddon Hts., N.J. 08035
`
`[21]
`
`Appl. No.: 444,644
`
`[22]
`
`Filed:
`
`Dec. 1, 1989
`
`[51]
`[52]
`[58]
`
`Int. Cl.’................................................ A61B 5/04
`U.S. Cl. .................................... 128/702; 128/696;
`128/710
`Field of Search ........................ 128/696, 700–708,
`128/710
`
`
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`3,832,994 9/1974 Bicher et al. ........................ 128/702
`4,622,979 11/1986 Katchis et al. ...................... 128/702
`4,732,158 3/1988 Sadeh .................................. 128/702
`4,742,831 5/1988 Silvian ................................. 128/696
`4,896,677 1/1990 Kaneko et al. ...................... 128/696
`Primary Examiner—Francis Jaworski
`Assistant Examiner—George Manuel
`[57]
`ABSTRACT
`Apparatus for detecting, analyzing and recording car
`diac events includes a patient-wearable monitor detect
`ing cardiac events and cardiac rhythm and processing
`information indicative of those events and rhythm to
`detect presence of a disturbance in the monitored
`rhythm by recording selected data from the patient's
`electrocardiogram before, during and after a detectd
`cardiac rhythm disturbance.
`
`19 Claims, 11 Drawing Sheets
`
`FITBIT, INC. v. LOGANTREE LP
`Ex. 1008 / Page 1 of 26
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`U.S. Patent
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`July 2, 1991
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`July 2, 1991
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`July 2, 1991
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`July 2, 1991
`July 2, 1991
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`Ex. 1008/ Page 5 of 26
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`Ex. 1008 / Page 5 of 26
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`Ex. 1008/ Page 6 of 26
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`Ex. 1008 / Page 6 of 26
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`July 2, 1991
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`July 2, 1991
`July 2, 1991
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`U.S. Patent
`U.S. Patent
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`July 2, 1991
`July 2, 1991
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`July 2, 1991
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`Ex. 1008 / Page 10 of 26
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`Ex. 1008 / Page 10 of 26
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`

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`U.S. Patent
`
`July 2, 1991
`
`Sheet 10 of 11
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`

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`U.S. Patent
`
`July 2, 1991
`
`sheet i? of 11
`
`5,027,824
`
`
`
`FIG 1
`
`Ex. 1008 / Page 12 of 26
`
`

`
`10
`
`15
`
`30
`
`METHOD AND APPARATUS FOR DETECTING,
`ANALYZING AND RECORDING CARDIAC
`RHYTHM DISTURBANCES
`FIELD OF THE INVENTION
`The principal focus of this invention is towards appa
`ratus and methods for detecting, analyzing and record
`ing cardiac rhythm patterns, particularly cardiac
`rhythm disturbances, for subsequent analysis, diagnosis
`and treatment of cardiac rhythm disturbances by physi
`cians. In addition to detecting, analyzing and recording
`cardiac rhythm patterns, the invention has applicability
`to monitoring other physiological signals such as tern
`perature, blood pressure, brain waves and the like.
`LEXICOGRAPHY
`Because this invention relates both to medicine, par
`ticularly cardiology, to electrical engineering and to
`20
`software, the following glossary of terms is provided
`respecting the prior art and the invention disclosed
`herein:
`ADM Technique—A method for digitizing an analog
`signal by comparing the analog signal to a signal de
`rived from the analog signal and producing a digitized
`25
`representation of the analog signal as a function of such
`comparison.
`Algorithm—A sequence of instructions directing
`performance of a specific task, such as moving informa
`tion or calculating values.
`Arrhythmia—Irregularity of heartbeat.
`Arrhythmic event—Cardiac behavior over a finite
`time period commencing with an arrhythmia.
`Artifact—Undesirable, extraneous components ap
`35
`pearing in an EKG as a result of muscle action and/or
`other external actions not related to cardiac function.
`Asymptomatic—Lack of patient awareness that a
`particular condition exists within the patient.
`Asystole—Absence of a heartbeat.
`Bradycardia—Slow heart rate.
`Complex—The portion of an EKG signal reflecting a
`single heartbeat.
`EKG/ECG Electrocardiogram—An analog signal
`reflecting electrical activity of the heart.
`Huffman Coding—A scheme for compressing digital
`data.
`R-wave—A specific portion of the electrocardio
`gram reflecting cardiac behavior during a correspond
`ing portion of a single heartbeat.
`ST Segment Analysis—Study of a specific portion,
`different from the R-wave, of the electrocardiogram
`reflecting cardiac behavior during a selected portion of
`a single heartbeat.
`Symptomatic—Patient awareness that a particular
`condition exists.
`Tachycardia—Fast heart rate.
`Ventricular—Having to do with the ventricular
`chamber of the heart.
`VPC/PVC/Premature Ventricular Contraction—a
`single heartbeat occurring earlier than expected.
`BACKGROUND OF THE INVENTION
`Analysis of electrocardiogram data taken over ex
`tended periods provides clinically significant informa
`tion which is important in the diagnosis and treatment
`of cardiac disease. Long-term recording of electrocar
`diographic data, commonly referred to as “Holter”
`monitoring, is a standard, accepted technique for elec
`
`5,027,824
`2
`trocardiographic analysis. This amounts to recording
`electrocardiogram data over a period of time and subse
`quently analyzing that data for rhythmic and morpho
`logical changes.
`Presently used monitoring devices for ambulatory
`patients are adequate for recording electrocardiogram
`data over twentyfour hour periods. However, presently
`used devices have limitations which come into play
`when longer term recording of electrocardiogram data
`is necessary.
`Often it is desirable to monitor cardiac rhythm and
`disturbances in cardiac rhythm when the disturbances
`are highly variable in frequency or when the frequency
`of disturbances is very low. Current practice is to em
`ploy repetitive twenty-four hour cardiogram monitors.
`However, this is very expensive and results in signifi
`cant discomfort to the patient due to the substantial size
`of the recording device required to record cardiac
`rhythm over twenty-four hour and longer periods.
`For other patients, whose arrhythmia is symptomatic
`(meaning that the arrhythmia is related to a particular
`condition occurring in the patient's body which the
`patient can sense) a patient-activated cardiac event re
`corder is often used. These patient-activated cardiac
`event recorders are limited in the data they provide
`because the recorder must be activated by the patient.
`Obviously, if the arrhythmic event incapacitates the
`patient, the patient cannot activate the cardiac event
`recorder. Also, if the arrhythmic event is asymptom
`atic, a patientactivated cardiac event recorder cannot be
`used because the patient does not know when his or her
`arrhythmia is occurring.
`Applicants are aware of printed prior art consisting of
`U.S. Pat. Nos. 4,123,785; 4,231,374; 4,333,475; 4,336,810
`and 4,667,682.
`The '785 patent discloses a cardiac event recorder for
`recording cardiac events over a defined twenty-four
`hour period. This device has the disadvantage associ
`ated with all patientactivated devices, namely if the
`arrhythmic event incapacitates the patient, the patient
`cannot activate the cardiac event recorder. Similarly, if
`the arrhythmic event is asymptomatic, a patient
`activated device will never be turned on to record the
`arrhythmic event.
`The '475 patent uses a microcomputer to continu
`ously monitor analog electrocardiogram signals and
`execute algorithms to classify each heartbeat and tally
`abnormal events such as arrhythmia.
`Similarly to '475, the 3 374 patent discloses a device
`and method for constantly monitoring heartbeat and
`activating circuitry upon occurrence of an abnormal
`heartbeat or other arrhythmic event to determine
`whether additional arrhythmic events occur during a
`selected subsequent monitoring period.
`The '810 patent discloses method and apparatus for
`analyzing a Holter-type electrocardiogram utilizing a
`tape playback unit having an analog signal output repre
`senting electrocardiogram complexes.
`The '682 patent discloses an ambulatory electrocar
`diogram recorder that senses tachycardia and 5radycar
`dia conditions and activates a tape recorder for a period
`of fifteen seconds after a traycardia or bradycardia
`event is detected.
`SUMMARY OF THE INVENTION
`In one of its aspects, this invention provides apparatus
`for detecting, analyzing and recording cardiac events,
`
`45
`
`50
`
`55
`
`65
`
`Ex. 1008 / Page 13 of 26
`
`

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`10
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`15
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`25
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`5,027,824
`4
`3
`cardiac event monitoring unit/arrhythmia analysis
`particularly cardiac rhythm disturbances. The appara
`module worn by the patient.
`tus aspect of the invention includes a patient-wearable
`FIG. 10 is a schematic block diagram of the preferred
`means for monitoring cardiac events and cardiac
`embodiment of the digital circuitry used in the cardiac
`rhythm and for processing signals indicative of cardiac
`event monitoring unit/arrhythmia analysis module
`events and particularly cardiac rhythm disturbances.
`worn by the patient.
`The patient-wearable cardiac event monitoring and
`FIG. 11 is a perspective view of the cardiac event
`signal processing means preferably includes means for
`monitoring unit/arrhythmia analysis module as worn by
`continuously monitoring cardiac rhythm and, option
`the patient.
`ally, other parameters indicative of cardiac status. Such
`In the drawings, circuit elements which are substan
`monitoring is performed via electrocardiogram leads
`tially functional equivalents of one another in different
`connected to a patient. The patient-wearable cardiac
`embodiments of the invention are indicated using the
`event monitoring means further includes means for
`same number. In some cases, prime notations associated
`detecting presence of a disturbance in the monitored
`with the number identifying a circuit element are used
`cardiac rhythm. The patient-wearable monitoring
`to indicate that such circuit element is a part of the
`means further includes means, operative responsively to
`preferred embodiment of the apparatus of the invention.
`the cardiac rhythm disturbance detecting means, for
`recording selected data from the patient's electrocardio
`DESCRIPTION OF THE PREFERRED
`gram before, during and after the detected cardiac
`EMBODIMENTS AND BEST MODE KNOWN
`rhythm disturbance. The means which is operative re
`FOR PRACTICING THE INVENTION
`sponsive to the cardiac rhythm disturbance detecting
`20
`Referring to FIG. 1, a microprocessor 2 has con
`means preferably further includes means for periodi
`nected to it a data memory unit 4, a program memory
`cally recording cardiac data, in addition to cardiac
`unit 6, a digital parallel port 12, a clock-calendar unit 14
`rhythm, which is indicative of cardiac function.
`and a clock oscillator 15. Digital parallel port 12 con
`In the apparatus aspect, the invention may yet further
`nects an analog-to-digital converter 22, having a multi
`include a base station for receiving the recorded and
`plexer as a part thereof, to microprocessor 2. The down
`analyzed cardiac event and arrhythmia data, for further
`wardly extending arrows in FIG. 1 denote plug con
`analyzing the data which are indicative of cardiac func
`nectable connections for connecting selected modules,
`tion, to provide information helpful to a cardiologist or
`each having components adapted to perform different
`other health professional.
`monitoring functions, to microprocessor 2 and associ
`BRIEF DESCRIPTION OF THE DRAwiNGs
`ated components illustrated in FIG. 1. The preferred
`selected module for connection to the microprocessor 2
`FIG. 1 is a block diagram schematically illustrating a
`and associated components illustrated in FIG. 1 is an
`portion of the patient-wearable cardiac event monitor
`arrhythmia analysis module, described below.
`ing unit.
`FIG. 2 schematically illustrates a particular module,
`FIG. 2 is a block diagram similar to FIG. 1 showing
`35
`specifically a preferred arrhythmia analysis module,
`in schematic form an arrhythmia analysis module con
`plugconnected to the cardiac event monitoring unit
`nected to the cardiac event monitoring unit illustrated
`illustrated schematically in FIG. 1. The broken line in
`schematically in FIG. 1.
`FIG. 2 denotes the plug connection interface between
`FIG. 3 is a schematic diagram of one embodiment of
`the cardiac event monitoring unit and the arrhythmia
`digital circuitry which may be used in the cardiac event
`40
`analysis module.
`monitoring unit and arrhythmia analysis module worn
`The arrhythmia analysis module may or may not be
`by the patient.
`fabricated on a printed circuit board separate from the
`FIG. 4 is a schematic diagram of one embodiment of
`circuitry of the cardiac event monitoring unit. Plug
`analog circuitry which may be used in the cardiac event
`connection between the cardiac event monitoring unit
`monitoring unit and arrhythmia analysis module.
`45
`and the arrhythmia analysis module is preferable and,
`FIG. 5 is a schematic diagram of a preferred embodi
`accordingly, it is most desirable that the circuitry of the
`ment of differential amplifier circuitry used as a portion
`cardiac monitoring unit be on a printed circuit board
`of the analog circuitry in a preferred embodiment of the
`separate from circuitry of the arrhythmia analysis mod
`cardiac event monitoring unit/arrhythmia analysis
`ule. Plug connection permits removal of the arrhythmia
`module worn by the patient.
`50
`analysis module and substitution of another analysis
`FIG. 6 is a schematic diagram of a preferred embodi
`module connected to the cardiac event monitoring unit
`ment of low pass filter circuitry used as a portion of the
`so that other physiological phenomenon can be de
`analog circuitry in a preferred embodiment of the car
`tected, analyzed and recorded, if desired.
`diac event monitoring unit/arrhythmia analysis module
`In FIG. 2 the arrhythmia analysis module includes an
`worn by the patient.
`55
`infrared information sensing transistor and diode unit
`FIG. 7 is a schematic diagram of a preferred embodi
`10, an alarm 20, function specific arrhythmia module
`ment of high pass filter circuitry used as a portion of the
`power control logic 38, gain control circuitry 34, gain
`analog circuitry in a preferred embodiment of the car
`stage circuitry 36, bias stage circuitry 30, high pass filter
`diac event monitoring unit/arrhythmia analysis module
`circuitry 40, low pass linear phase filter circuitry 32, .
`worn by the patient.
`60
`instrumentation amplifier circuitry 42, motor drive con
`FIG. 8 is a schematic diagram of a preferred embodi
`trol 24, a tape head drive 27, tape heads 29 and regula
`ment of offset adjust circuitry used as a portion of the
`tor(s) 21. As further evidenced from FIG. 2, gain stage
`analog circuitry in a preferred embodiment of the car
`circuitry 36 is connected to digital parallel port 12 lead
`diac event monitoring unit/arrhythmia analysis module
`ing to microprocessor 2 via gain control 34. Gain stage
`worn by the patient.
`65
`circuitry 36 is further connected to microprocessor 2
`FIG. 9 is a schematic diagram of a preferred embodi
`via digital parallel port 12 by means of analog-to-digital
`ment of adjustable gain stage circuitry used as a portion
`converter with multiplexer timer 22. Apparent from
`of the analog circuitry in a preferred embodiment of the
`
`30
`
`Ex. 1008 / Page 14 of 26
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`multiplexer 22. Preferably, the remaining lines are re
`FIG. 2, the arrhythmia analysis module has multiple
`served for a particular application module such as the
`connections to digital parallel port 12 including gain
`arrhythmia analysis module.
`control 34, powered down circuitry 38 which is some
`Analog-to-digital converter with multiplexer 22
`times referred to as function specific module power
`serves to digitize analog signals for analysis by micro
`control logic circuitry, infrared serial input/output port
`processor 2 or for storage in the random access memory
`10, alarm 20, motor control circuitry 24 and tape head
`portion of data memory unit 4 or for recording on mag
`control circuitry 27. Input signals arrive at the first
`netic tape by tape heads 29. A single analog-to-digital
`differential amplifier stage or circuitry 42 which con
`converter can digitize several sources of analog signals;
`nects in turn to low pass filter circuitry 32, high pass
`hence, an analog multiplexer is included as a portion of
`filter circuitry 40, offset adjustment circuitry 30 and
`unit 22. The analog multiplexer allows microprocessor
`adjustable gain stage circuitry 36. Adjustable gain stage
`2 to select one of several analog signals to pass through
`circuitry 36 also connects to gain control circuitry 34
`to the analog-to-digital converter for digitization. When
`and to analog-to-digital converter/multiplexer 22.
`the cardiac event monitor is working with the arrhyth
`As further apparent from FIG. 2, in the preferred
`mia analysis module, preferably one analog channel is
`embodiment gain stage circuitry 36 connects to bias
`used. The channel carries the electrocardiogram signal,
`stage circuitry 30. This bias stage circuitry 30 is in turn
`conditioned to comply with AAMI standards for diag
`connected to high pass filter circuitry 40. This high pass
`nostic electrocardiographic devices. Optionally, a sec
`filter circuitry 40 is in turn connected to low pass linear
`ond channel may also be used, carrying the same elec
`phase filter circuitry 32, which in turn is connected to
`trocardiogram signal, but being much more heavily
`instrumentation amplifier 42. In the preferred embodi
`20
`filtered and conditioned. Microprocessor 2 may use
`ment, input signals first arrive at differential amplifier
`either the optional heavily filtered and conditioned
`stage 42 for processing thereby and by the elements
`signal or the signal as conditioned only to the extent to
`schematically illustrated connected in series leading
`comply with AAMI Standards to determine whether a
`away from differential amplifier stage 42.
`cardiac event has occurred. Whether or not the heavily
`While motor 26 is shown schematically in FIG. 2,
`25
`filtered signal is used, the lightly filtered electrocardio
`motor 26 does not form any portion of the arrhythmia
`gram signal is stored in the random access memory
`analysis module; motor 26 is an integral part of the
`portion of data memory unit 2 and, if it is determined
`apparatus of the invention because motor 26 serves to
`after analysis that a cardiac event has occurred, is also
`drive the tape recorder portion of the apparatus of the
`stored by recording on the magnetic tape of the tape
`30
`invention.
`recorder. In the preferred practice of the invention,
`The circuit elements in FIG. 1 are preferably static,
`only a single channel is used. Microprocessor 2 uses the
`complementary metal oxide silicon (CMOS) circuit
`electrocardiogram signal in an only lightly conditioned
`elements. These CMOS elements provide low power
`form, preferably conditioned only to the extent to com
`consumption.
`ply with all AAMI standards, to determine whether a
`Further referring to FIG. 1, microprocessor 2 is pref
`35
`cardiac event has occurred.
`erably a member of the 6502 family. Specifically, micro
`If desired, the software in microprocessor 2 can be
`processor 2, shown with prime notation in FIG. 10, is
`programmed so that alarm 20 signals the patient as to
`preferably a Rockwell R65C02, package PLCC-44, part
`occurrence of a given, predetermined state. Depending
`number R65C02]l, microprocessor of the 6502 family.
`on the option selected during programming, alarm 20
`An optional power control logic unit 18, shown as a
`40
`may sound upon detection of a hardware problem such
`part of the arrhythmia analysis module in dotted lines in
`as a low battery, low tape remaining or the like. Alter
`FIG. 2, may consist of a logic array and a number of
`natively, the alarm may sound because the cardiac mon
`low power analog switches. The optional power con
`itor has recognized a cardiac event. The user has the
`trol logic unit 18 may be used to power down the unit,
`option to have alarm 20 sound in the event of only
`to a low power, quiescent operating state, during peri
`45
`certain types of arrhythmias, or upon occurrence of any
`ods of inactivity.
`arrhythmias, according to programming of the system.
`The program memory 6 contains all of the fundamen
`Clock/calendar unit 14 maintains the date and time.
`tal subroutines required for operation of the cardiac
`Clock/calendar unit 14 preferably is contained within
`monitor circuitry. These sub-routines include those
`digital parallel port 12.
`performing analog-to-digital conversion, analog multi
`50
`plexing, power control, tape control, tape recording,
`When a cardiac event has occurred and the random
`access memory of data memory unit 4 is full, the cardiac
`serial communications and data compression. Data
`event data is recorded on magnetic tape by a tape re
`memory 4 serves as the read-write random access mem
`corder driven by motor 26. Microprocessor 2 instructs
`ory for microprocessor 2. Program variables and stacks
`digital parallel port 12 to generate a motor control sig
`are stored in the random access memory portion of data
`nal as input to motor drive control 24, which turns
`memory 4. Preferably infrared serial input/output unit
`motor 26 on and off based on control commands re
`10 may be provided to communicate with the base sta
`ceived from microprocessor 2. The design goal has been
`tion portion of the apparatus of the invention. The base
`to achieve time response of microprocessor 2 and motor
`station is preferably a personal computer. Preferably
`drive control 24 such that the motor is up to proper
`infrared serial input/output unit 10 communicates with
`speed in approximately eight one-thousandths (0.008)
`the base station via an infrared sensing transistor and
`seconds and stops in the same time or even less.
`diode unit, which eliminates the need for a cable con
`Drive motor 26 may be a pulse/continuous motor
`nector between the base station computer and the car
`having a time constant of approximately seven millisec
`diac event monitor.
`onds. In one - practice of the invention, motor 26 has
`Digital parallel port 12 includes general purpose digi
`65
`been driven by a regulated voltage of nominally 2.2
`tal input/output lines. In the preferred embodiment of
`volts. Drive motor 26 should stop almost instantly upon
`the invention, certain of these digital input/output lines
`a short circuit of its input. Since drive motor 26 has a
`are dedicated to control the analog-to-digital converter
`
`15
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`Ex. 1008 / Page 15 of 26
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`25
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`30
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`15
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`7
`unit and arrhythmia analysis module protect the cir
`design goal of reaching running speed at about five
`cuitry against adverse consequences in the event the
`times its time constant or in about 35 milliseconds and
`since creating a true short circuit at the input for drive
`batteries short-circuit.
`-
`Referring to FIG. 2, instrumentation amplifier 42,
`motor 26 is not straightforward, the start and stop times
`sometimes descriptively referred to as differential am
`of the motor may be controlled using specially shaped
`plifier 42, preferably utilizes three quarters of two Pre
`motor pulses produced by motor drive control circuitry
`cision Monolithics, Inc. Quad Precision operational
`24. This approach reduces wasted tape space, particu
`amplifiers, package SOL-16, part number OP490GS, to
`larly in applications where only small quantities of data.
`obtain a quality single lead of electrocardiogram signal,
`are recorded, either periodically or aperiodically.
`as shown in greater detail in FIGS. 4 and 5. The instru
`In one practice of the invention, a Radio Shack mi
`10
`mentation amplifier circuitry designated generally 42 in
`cro-26 cassette recorder has provided the basis for the
`FIG. 2 and in FIG. 4 and 42' in FIG. 5 has a differential
`tape recorder in the cardiac monitor unit.
`input with high impedance and high common mode
`Battery module 16 preferably houses two Electro
`rejection. Signals from the two electrodes of an electro
`chem 3B793-TC lithium batteries. While lithium batter
`cardiogram measuring device, designated 44, 46, are the
`ies are currently preferred, zinc-air, aluminum-air or
`plus and minus inputs to instrumentation amplifier 42 or
`alkaline batteries may also possibly be used with the
`42'. A third electrode 48 from the electrocardiogram
`invention. Having these two on-board batteries is one
`acts as a reference and is connected to the negative
`approach permitting use of voltages below an arbitrary
`ground for the analog circuitry portion of the invention,
`local ground level. With this approach, stop time of
`as indicated by the inverted triangle with the subscript
`motor 26 may be virtually equivalent to that which
`20
`A in FIG. 5. (The analog circuitry portion of the inven
`would be experienced if the input to motor 26 was
`tion, as disclosed in two embodiments, is generally
`short-circuited. Motor 26 start time may be reduced as
`shown in FIGS. 4 through 9 of the drawings. The in
`a result of improved acceleration at motor turn-on pro
`verted triangle with the subscript A is used throughout
`vided by appropriately shaping the run-pulse onset volt
`the drawing figures to denote ground reference for the
`age versus time curve.
`analog portion of the circuitry of the invention. For the
`One design goal is to have the capstan of motor drive
`digital portion of the circuitry of the invention, a
`26 operate at about 7,500 revolutions per minute, to
`ground reference is indicated in the drawings by the
`drive a 181:1 reduction gear train. One design goal for
`conventional ground symbol, consisting of four parallel
`motor output shaft rotation is about 0.6906 revolutions
`horizontal lines of decreasing length, disposed in a gen
`per second. The design goal for motor torque is about
`erally triangular shape. This symbol is used extensively
`0.052 inch-ounces with the gear train output torque
`in FIG. 3.)
`being about 9.412 inch-ounces, which is far above that
`In FIGS. 4 and 5, where circuitry of instrumentation
`required by the tape recorder for tape movement.
`amplifier 42 or 42' is shown in greater detail, three sec
`Another design goal is to have the drive motor cap
`tions of the OP490 operational amplifier identified
`stan with a diameter of about 0.1248 inches, to result in
`35
`herein as differential amplifier 42 are designed 50, 52
`a circumference of about 0.3921 inches. When the
`and 54. Further respecting instrumentation amplifier 42,
`motor capstan is driven at the design goal of about
`output of operational amplifier 50 is provided as feed
`0.6906 revolutions per second, the magnetic tape should
`back to the negative input terminal thereof via resistor
`move at a rate of about 0.2708 inches/second. Assuming
`230. This signal is also provided, through resistor 232 to
`a conservative pulse-packing factor of 4,500 bits/inch/
`combine with output signal from operational amplifier
`track, this means that it should be possible to write on
`52 as provided through resistor 234 as feedback input to
`the tape every 222×10-6 inches at a data-writing rate
`the negative input terminal of operational amplifier 52.
`of 1,220 nibbles/second, assuming a four-track tape.
`Output of operational amplifier 50 is also provided via
`Lithium thionyl chloride batteries may be used in
`resistor 236 for combination with output from opera
`place of the preferred Electrochem lithium batteries 45
`tional amplifier 54 provided through resistor 238 for
`noted above. Such lithium thionyl chloride batteries
`input to the negative input terminal of operational am
`have extremely stable voltage levels, very high energy
`plifier 54. Output of operational amplifier 52 is provided
`capacity per unit volume and extremely low density. If
`through resistor 240 as input to the positive input termi
`95% of the capacity of the batteries is used, such a
`nal of operational amplifier 54. Resistor 242 connects
`battery pair should easily accommodate between six
`the positive input terminal of operational amplifier 54 to
`and twelve patients each using the cardiac monitor
`a voltage source.
`apparatus of the invention for seventeen days or less.
`Referring again to FIG. 2, high pass filter circuitry 40
`One of the advantages of the invention is that the
`removes the DC component from the electrocardio
`cardiac monitor unit may be programmed, using suit
`gram signal after processing by instrumentation ampli
`able algorithms, to automatically calculate its own bat
`55
`fier 42. High pass filter circuitry 40 is preferably a single
`tery usage and to report such battery usage information
`pole passive circuit which passes frequencies of 0.1
`to the base station computer via the infrared coupling
`Hertz and higher. One embodiment of high pass filter
`provided by infrared sensing transistor and diode unit
`circuitry 40 is shown in greater detail in FIG. 4. High
`10. Accordingly, the base station computer may inform
`pass filter circuitry 40, capacitor 58 and resistor 60 pro
`the medical technician or physician of battery status and
`vide filtered input to operational amplifier 56 for pro
`may specify when batteries in a cardiac monitor unit
`cessing to produce an output signal from high pass filter
`according to the invention must be changed. A safety
`circuitry 40.
`factor may be built-in to insure that the batteries in the
`The preferred embodiment of high pass filter cir
`cardiac monitor unit do not run out while the unit is
`cuitry is illustrated in FIG. 7 where the filter circuitry
`being worn by a patient. The batteries should be de
`65
`receives input signal as indicated by III and includes a
`signed so that short-circuiting produces no serious or
`dangerous consequence to the patient; appropriately
`capacitor 58', a resistor 59', a resistor 60' and diodes 61'
`applied diodes throughout most of the cardiac monitor
`and 63' connected in the manner illustrated between the
`
`50
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`Ex. 1008 / Page 16 of 26
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`stage 36 through resistor 88 with both the output of gain
`main signal line and analog ground. Capacitor 58' is
`stage 36 and the feedback of operational amplifier 80
`preferably a 2.2 microfarrad Illinois capacitor part num
`being joined prior to application to the negative input
`ber 225BPR050MXXAF. Resistor 59' is preferably a 1
`terminal, operational amplifier 80. The positive input
`K ohm carbon film resistor. Resistor 60' is preferably a
`terminal operational amplifier 80 is connected to
`1 M ohm carbon film resistor. Diodes 61, and 63, are
`preferably Motorola MMBD914 diodes. Output of high
`ground, as shown.
`The pre