United States Patent
`
`1191
`
`t
`
`1111
`
`3,886,950
`
`
`
`[45]Ukkestad et a1. June 3, 1975
`
`
`
`[54] DEFIBRILLATOR
`[75]
`Inventors: Donald C. Ukkestad, Newbury Park;
`Donald C. Hancock, Thousand
`
`Oaks; Donley J. Valiquette,
`Camarillo, all of Calif.
`
`.
`_
`[73] Assrgnee: Spacelabs, Inc., Chatsworth, Calif.
`[22]
`Filed:
`Oct. 1, 1973
`
`[21] AWL N0": 402’401
`
`[52] US. Cl.............................................. 128/419 1)
`[51]
`Int. Cl............................................... A6111 1/36
`[58] Field of Search ..................... 128/419 D, 419 R
`
`[56]
`
`References Cited
`UNITED STATES PATENTS
`3 359 984
`128/419 D
`12/1967 Daniher et al
`3’655’754
`9/1971
`Jams et a1“...'.::::::IIII: 128/419 D
`
`3:706:313
`12/1972 Milani m a] .................... 128/419 D
`3,747,605
`7/1973 Cook
`128/419 D
`3,782,389
`1/1974
`Bell ................................. 128/419 D
`FOREIGN PATENTS OR APPLICATIONS
`272,021
`7/1964 Australia......................... 128/419 D
`
`Primary Examiner—William E. Kamm
`Attorney, Agent, or Firm—Fraser and Boqueki
`
`ABSTRACT
`[57]
`A defibrillator is disclosed which regulates the magni-
`tude of a current pulse delivered to a patient in accor-
`dance with a selected value of current and which
`quickly terminates the current pulse when the mea-
`sured energy delivered to the patient equals a selected
`value. Current regulation is accomplished by circuitry
`which compares current actually flowing through the
`patient with the selected value and which utilizes the
`results of such comparison to sequentially discharge a
`plurality of capacitors serially coupled to the patient
`electrodes. Further circuity multiplies the current
`through the patient hy the voltage measured. across
`the patient to determine power with the resulting sig-
`“31 bemg ‘megra‘ed relat‘le ‘0 “me to "‘dlcate dehv’
`ered energy When the delivered energy equals the se-
`lected value of energy, the electrodes are shunted by
`circuitry which terminates the current pulse to the pa-
`tient and which dischar es all ca acitors not alread
`discharged.
`g
`p
`y
`12 Claims, 4 Drawing Figures
`
`26
`24
`58
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`
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`- CAPACITOR
`.
`POWER
`
`
`SOURCE
`DISCHARGE
`1
`PATIENT
`
`.
`"
`CIRCUITS
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`
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`CAPACITORS ‘
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`I
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`ENERGY
`CONTROL
`
`
`
`CIRCUIT
`COMPUTER
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`
`
`
`
`34
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`ENERGY
`ENERGY
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`
`
`SELECTION
`DISPLAY
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`
`
`
`
`1
`
`L|FECOR905-1008
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`1
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`
`

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`POWER
`
`TRUNCATE
`I
`PATIENT
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`DISCHARGE
`
`SOURCE
`CAPACHORS
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`CIRCUITS
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`30
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`CONTROL
`CIRCUIT
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`34
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`ENERGY
`SELECHON
`
`FIG.—2
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`NOMINAL CURRENT
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`
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`DELWERED
`CURRENT
`
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`

`1
`DEFIBRILLATOR
`
`3,886,950
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention relates to defibrillators of the
`type which apply a controlled amount of current to a
`patient to stop fibrillation of the patient’s heart.
`2. History of the Prior Art
`The effects of electrical shocks on persons have been
`carefully studied. It has been found, for example, that
`shocks producing currents in the range of 2 to 50 milli-
`amperes through the body will be felt as a tickling or
`other strange sensation but usually will not result in se—
`rious harm. On the other hand, currents through the
`body which are in the range of50 milliamperes to 2 am-
`peres often result in fibrillation of the person’s heart.
`Currents greater than 2 amperes typically do not pro-
`duce fibrillation, but may result in other bodily damage
`including eventual burning or destruction of the tissues
`if the current becomes too large.
`Fibrillation is defined as an uncoordinated movement
`of the ventricular walls of the heart.
`It
`is typically
`caused by an electrical shock within the 50 milliampere
`to 2 ampere range as noted above, but also can result
`from a coronary heart attack. In fibrillation the blood
`circulation ceases, and death results if the condition is
`not treated promptly.
`Much experimentation has been done in the area of
`stopping heart fibrillation. One technique which has
`been found to be generally successful involves the ap-
`plication of electrical shocks to the patient through a
`pair of electrodes contained within paddles. Research
`in this area has involved the use of a variety of different
`waveforms and amplitudes. While the shock or defibril-
`lation signals of different waveforms and amplitudes
`have met with varying degrees of success in many in-
`stances, it has been found that a single current pulse of
`generally rectangular waveform is among the most suc-
`cessful of the shock signals used in this type of therapy,
`particularly if the magnitude of the current pulse is well
`above 2 amperes and on the order of 10 to 20 amperes.
`The current pulse must also have relatively short rise
`and fall times. The fall of the current pulse must be par—
`ticularly rapid through the 2 ampere to 50 milliampere
`range. Otherwise fibrillation may again set in. Discus-
`sions of the involved problems and some of the current
`techniques are given in a number of articles including
`“Transthoracic Ventricular Defibrillation with Square-
`wave Stimuli: One—Half Cycle, One Cycle, and Multicy—
`cle Waveforms", Schuder, Stoeckle and Dolan, Circu-
`lation Research, September,
`1964, pp.
`258—264;
`“Transthoracic Ventricular Defibrillation In The Dog
`With Truncated And Untruncated Exponential Stim-
`uli”, Schuder, Stoeckle, West and Keskar,
`IEEE
`TRANSACTIONS ON BIO—MEDICAL ENGINEER-
`ING, Volume BME—l8, Number 6, November, 1971,
`PP- 410—4 15; “Transthoracic Ventricular Defibrillation
`with Triangular
`and Trapezoidal Waveforms”,
`Schuder, Rahmoeller and Stoeckle, Circulation Re-
`search, October, 1966, pp. 689—694; and “Transtho-
`racic Ventricular defibrillation with a very high ampli—
`tude rectangular pulses", Schuder, Rahmoeller, Nellis,
`Stoeckle . and MacKenzie,
`J. Appl.
`Physiol.
`22“”:1110—1 114, 1967.
`One common approach to the problem of generating
`a defibrillation current pulse has been to employ one or
`a Plurality of capacitors which are initially charged to
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`10
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`2
`a selected level. Where a single capacitor is employed
`the capacitor is thereafter discharged at the selected
`moment to provide a current pulse through the patient.
`Where plural capacitors are employed, such capacitors
`are typically discharged simultaneously so that the ef»
`fects thereof may be summed together to provide de—
`sired levels of current and voltage. Defibrillators of this
`type are typically relatively large, heavy and expensive,
`not only because of the size of the capacitor or capaci-
`tors, but also because of the presence of a large choke
`and vacuum relay which are frequently employed in
`such devices.
`Perhaps of even greater importance, however, is the
`fact that prior art defibrillators do not regulate deliv-
`ered current. The discharge of a single capacitor or the
`simultaneous discharge of plural capacitors provides a
`current pulse to the patient, the peak amplitude of
`which varies in accordance with the resistance of the
`patient’s body. Since patient resistance typically varies
`within a range of 30 to 150 ohms, it will be appreciated
`that the delivered current pulse can vary substantially
`from one patient to the next, and even in the case of the
`same patient where that patient’s body resistance varies
`for one reason or another. Consequently the capacitors
`must be chosen, charged and discharged so as to de—
`liver a current pulse of optimum shape to the patient
`when the patient’s body resistance is within an everage
`range. The practical result is that when the body resis—
`tance is above this range,
`the current pulse decays
`slowly, particularly within the 2 ampere to 50 milliam-
`pere danger zone inviting fibrillation to again set in. On
`the other hand, when the body resistance is too low, the
`current pulse decays rapidly but
`tends to oscillate
`within the 2 ampere to 50 milliamperc range, again in—
`viting fibrillation to set in.
`As a result, defibrillators of the prior art typically
`produce a current pulse which is more rounded than
`rectangular in shape and which does not have a rapid
`decrease at the trailing edge. Such units typically make
`no effort to regulate the current or to control the dura-
`tion of the current pulse in terms of delivering a se—
`lected amount of electrical energy to the patient.
`Accordingly, it would be desirable to provide a defi-
`brillator which generates current pulses of generally
`rectangular waveform having very short rise and fall
`times. It would furthermore be desirable to regulate the
`delivered current in accordance with sensings taken
`from actual body current. It would furthermore be ad-
`vantageous to provide a defibrillator in which the dura-
`tion of each current pulse may be selected to provide
`a desired amount of delivered energy to the patient.
`BRIEF DESCRIPTION OF THE INVENTION
`
`invention provides a defibrillator in
`The present
`which current pulses are regulated in accordance with
`actual current passing through the patient so as to
`maintain the current substantially at a selected nominal
`magnitude throughout
`the pulse. Measured voltage
`across the patient is used together with measured cur-
`rent through the patient to compute the electrical en-
`ergy delivered to the patient by each current pulse. The
`value of delivered energy may be used to abruptly ter-
`minate the current pulse when a selected amount of en-
`ergy has been delivered.
`In accordance with one aspect of the invention, the
`defibrillator may comprise a plurality of capacitors
`coupled to be charged in parallel and discharged in se-
`
`4
`
`

`

`3,886,950
`
`3
`ries. Upon commencement of a discharge cycle, one or
`more but not all of the capacitors are simultaneously
`discharged to commence generation of a current pulse.
`Thereafter, actual current through the patient is moni-
`tored and compared with a desired current value. The
`results of the comparison are used to sequentially dis-
`charge remaining ones of the capacitors to maintain the
`delivered current substantially at the selected value.
`The system thus maintains a substantially constant de—
`livered current through the patient independent of the
`patient’s body resistance. Defibrillators having plural
`capacitors utilized in this fashion are relatively com—
`pact and lightweight as well as inexpensive so as to be
`ideally suited for portable applications.
`Energy selection is accomplished by initially adjust—
`ing controls which provide a signal representing desired
`energy as well as a visual display of the desired energy
`for confirmation by the user. Upon generation ofa cur-
`rent pulse, the current actually flowing through the pa-
`tient as sensed is multiplied by the voltage across the
`patient to provide a representation of delivered power.
`The power representation is integrated with respect to
`time to provide a representation of delivered energy
`which is then compared with the energy reference or
`value initially selected. At the same time the visual dis-
`play is used to provide a visual indication of delivered
`energy. When the comparison process determines that
`the desired amount of energy has been delivered, the
`patient electrodes are shunted to terminate the current
`pulse to the patient. At the same time, all capacitors
`not already discharged are discharged through the
`shunt path to insure against subsequent accidental dis-
`charge through the patient.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The foregoing and other objects, features and advan-
`tages of the invention will be apparent from the follow-
`ing more particular description of a preferred embodi-
`ment of the invention, as illustrated in the accompany—
`ing drawings, in which:
`FIG. 1 illustrates use of a defibrillator in accordance
`with the invention in conjunction with a patient;
`FIG. 2 is a basic block diagram of a defibrillator in
`accordance with the invention;
`FIG. 3 is a diagrammatic plot of a Current pulse pro—
`duced by the defibrillator of FIG. 2; and
`FIG. 4 is a detailed block and schematic diagram of
`the defibrillator of FIG. 2.
`
`DETAILED DESCRIPTION
`
`FIG. 1 illustrates a patient 10 whose heart is in fibril-
`lation due to electrical shock, coronary or other com-
`mon cause. A defibrillator 12 is used to pass current
`pulses of selected shape and size through the patient 10
`using a pair of electrodes contained within a pair of
`paddles l4 and 16. The paddles l4 and 16 are respec-
`tively coupled by leads 18 and 20 to the defibrillator
`12. The defibrillator 12 may have to be coupled to a
`separate power source such as by plugging it into a
`electrical wall receptacle, or it may contain its own
`power source, typically in the form of batteries.
`Defibrillators are typically relatively large and heavy
`units which are best
`located in hospital emergency
`rooms and similar locations where they do not have to
`be moved about. However the present invention pro-
`vides for defibrillators which are not only more effec-
`tive than prior art units, but which can be made in very
`
`4
`small sizes and light weights. In particular, defibrillators
`according to the invention can be easily made into por-
`table units which can be carried much like a suitcase or
`similar piece of equipment to the patient. Such porta-
`ble defibrillators are ideally suited for use by emer-
`gency personnel and rescue squads which can easily
`carry the defibrillator to the scene of the accident or
`use it in an ambulance or other means of transporting
`the patient to a hospital or other medical facility.
`FIG. 2 illustrates a preferred form of defibrillator 22
`according to the invention.
`In the defibrillator 22, a
`power source 24- is coupled to charge a plurality of ca~
`pacitors 26. Charging of the capacitors 26 is initiated
`by a control located in one of a pair of paddles 28 and
`30 as described in conjunction with FIG. 4. The opti~
`mum magnitude of the current pulse to be delivered to
`the patient is selected by adjusting controls within a
`control circuit 32. At the same time the total energy to
`be delivered to the patient by each current pulse is se~
`lected via energy selection circuitry 34, the controls for
`which are located in one of the paddles 28 and 30 as
`described in conjunction with FIG. 4. The energy selec-
`tion circuitry 34 is coupled to an energy display 36
`which provides a visual indication of the amount of en—
`ergy which has been selected. The energy selection cir-
`cuitry 34 also provides a reference signal representing
`the desired amount of energy to the control circuit 32.
`A discharge cycle is begun by actuating controls
`within the paddles 28 and 30, thereby causing one or
`more of the capacitors 26 to discharge through the pa-
`tient. The number of capacitors chosen to initially dis-
`charge in this fashion is determined by the known char—
`acteristics of the unit as used with average patients. The
`number of capacitors initially discharged is selected so
`as to provide a voltage across the patient sufficient to
`quickly establish a current flow well above 10 amperes
`and typically on the order of 20 amperes through the
`patient. Thereafter the current delivered to the patient
`is regulated by the control circuit 32 and a plurality of
`capacitor discharge circuits 38 coupled to individual
`ones of the capacitors 26. The control circuit 32 does
`this by continually comparing the current actually flow-
`ing through the patient with the current reference ini-
`tially set by the user. Whenever the delivered current
`decreases below the reference, the control circuit 32
`causes one of the capacitor discharge circuits 38 to ini—
`tiate discharge of one of the capacitors 26 through the
`patient. This typically results in a momentary increase
`in the delivered current above the reference value, fol-
`lowed by a decrease in the current as discharge of the
`capacitor proceeds. Each time the delivered current
`falls below the reference, a new one of the capacitors
`26 is discharged by the control circuit 32 via the dis-
`charge circuits 38. Accordingly during the generation
`of a typical current pulse, one or two of the capacitors
`26 are initially discharged to begin the pulse, following
`which a selected number of the remaining capacitors
`are sequentially discharged to maintain the magnitude
`of the current pulse through the patient at the refer-
`ence level.
`
`During generation of the current pulse, an energy
`computer 40 measures the voltage across the patient as
`well as the current flowing through the patient. The
`current and voltage are multiplied, then integrated to
`provide a representation of the energy actually deliv—
`ered to the patient. The energy computer 40 is coupled
`to the display 36 to provide a visual display of delivered
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`3,886,950
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`energy. When the delivered energy equals the refer-
`ence value chosen by the energy selection circuitry 34,
`the energy computer 40 causes the control circuit 32
`and the associated capacitor discharge circuits 38 to
`initiate the discharge through the SCR truncate circuit
`42 of all capacitors which have not already been dis—
`charged. This is a safety feature which prevents a sub-
`sequent accidental current pulse from being generated.
`At the same time the SCR truncate circuit 42 termi—
`nates the current pulse by shunting the paddles 28 and
`38.
`If another current pulse is necessary to defibrillate
`the patient’s heart, the above-described process is re-
`peated with the capacitors 26 being charged by the
`power source, the energy being selected via the selec-
`tion circuitry 34 and the current being selected within
`the control circuit 32. Thereafter a discharge cycle is
`again initiated with the control circuit 32 and associ-
`ated capacitor discharge circuits 38 acting to regulate
`the current actually flowing through the patient while
`the energy computer 40 monitors the delivered energy
`and initiates truncation and total capacitor discharge
`when the selected energy has been delivered.
`A typical current pulse produced by the defibrillator
`22 of FIG. 2 is illustrated in FIG. 3. When a discharge
`cycle is initiated by discharging one or two of the ca-
`pacitors, the current through the patient rises to a peak
`44 which is above the selected nominal or reference
`value represented by a dashed line 46. As shown in
`FIG. 3, this provides the current pulse with a very fast
`rise time, which is a highly desirable feature as previ—
`ously noted. The selected capacitor or capacitors dis—
`charge causing the delivered current to decrease to a
`point 48 at which it equals the reference current se~
`lected within the control circuit 32. The control circuit
`32 responds by causing one of the capacitor discharge
`circuits 38 to initiate discharge of one of the capacitors
`26. This causes the delivered current to increase to a
`point 50 from which it again decreases to a point 52.
`The process is again repeated with the control circuit
`32 causing discharge of another one of the capacitors
`26 to increase the current to a point 54 from which it
`again decays. The process continues with the capaci-
`tors 26 being sequentially discharged to maintain the
`delivered current equal to or slightly above the refer-
`ence or nominal value until the energy computer 40
`and the control circuit 32 determine that the selected
`amount of energy has been delivered. As the SCR trun-
`cate circuit 42 is activated to shunt the paddles 28 and
`30, the current drops very rapidly to zero. This pro-
`vides a very short fall time which is an essential feature
`for successful operation as previously noted.
`One preferred form of a defibrillator 22 in accor-
`dance With the invention is shown in detail in FIG. 4.
`In this particular arrangement, the right paddle 30 is
`provided with a switch 50, the closure of which com—
`pletes a circuit through a sample-hold switch 52 and via
`a lead 54 to a pulse width modulated inverter 56 within
`the power source 24. The pulse width modulated in—
`verter 56 functions to increase the voltage of the power
`supply in the form of a battery 58 at the primary side
`of a transformer 60. The transformer 60 has a plurality
`of different secondaries, each of which is associated
`with a different one of the capacitors 26. In the present
`example eight capacitors are used, although only three
`of the corresponding circuits are shown for simplicity
`of illustration. The parallel arrangement of the trans-
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`the simultaneous
`former secondaries provides for
`charging of the capacitors 26. In the present example,
`the capacitors are 540 microfarads in value and are
`charged to a voltage of approximately 450 volts each.
`A diode 62 within each capacitor circuit insures charg-
`ing of the associated capacitor in a sense as shown in
`FIG. 4.
`Current selection is carried out within the control cir-
`cuit 32 by a circuit which comprises a pair of fixed re-
`sistors 64 and 66 and a variable resistor 68, all of which
`are coupled between a positive supply terminal 70 and
`ground. The wiper arm of the variable resistor 68 is
`used to provide a signal representing the desired or ref
`erence current 1,; to a current control comparator 72.
`Energy selection is accomplished by a variable resis-
`tor 74 forming a part ofa circuit within the right paddle
`30. The sample-hold switch 52 remains closed during
`the charging cycle, causing a digital voltmeter 76 to
`compute and store a signal representing the energy ref-
`erence or selected energy ER. The sample-hold switch
`52 may comprise a circuit sold under the designation
`CD4016 by Radio Corporation of America. The digital
`voltmeter 76 provides the energy reference signal E, to
`a comparator 78 within the control circuit 32 as well as
`to an energy display 80. The energy display 80 includes
`a plurality of light~emitting diodes arranged to provide
`a visual display of the energy selected via the right pad-
`dle 30.
`
`A discharge cycle is commenced by simultaneously
`closing a pair of discharge switches 82 and 84 within
`the right and left paddles 30 and 28 respectively. This
`completes a circuit through the sample-hold switch 52
`and via a lead 86 to a sequence counter 88 within the
`control circuit 32. The sample-hold switch 52 is opened
`and remains open during the discharge cycle. The se-
`quence counter 88 which controls the discharge of the
`capacitors 26 via the discharge circuits 38 causes dis-
`charge of one or more of the capacitors 26 to begin the
`current pulse. Each of the capacitors is coupled by a
`different silicon controlled rectifier 90 to a common
`lead 92. The lead 92 includes a plurality of diodes 94
`individually coupled in parallel with different ones of
`the capacitors 26. Firing of any one of the silicon con—
`trolled rectifiers 90 by the sequence counter 88 causes
`current from the associated capacitor 26 to flow to the
`common lead 92 where the diodes 94 force the current
`to flow upwardly as seen in FIG. 4 to a common lead
`96. The lead 96 is coupled to an electrode 98 for con-
`nection to the patient via the left paddle 28. An elec—
`trode 100 within the right paddle 30 connects a differ-
`ent portion of the patient’s body to a return lead 102.
`Because of the particular arrangement of the capaci-
`tors 26 and the discharge circuits 38, the capacitors 26
`are effectively coupled in series across the patient. If
`more than one capacitor is initially discharged by the
`sequence counter 88, the voltages of the discharged ca-
`pacitors add together in serial fashion to provide a
`rapid rise of current to a value at least equal to the ref-
`erence current IR. In the present example, two of the
`eight capacitors 26 are typically discharged upon initia-
`tion of a discharge cycle to provide a suitable current
`pulse for most applications.
`A lead 110 couples the electrode 100 to provide a
`representation of the actual delivered current or cur~
`rent flowing through the patient's body 1,, to the current
`control comparator 72 within the control circuit 32 as
`well as to a current amplifier 112 within the energy
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`7
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`3,886,950
`
`computer 4-0. The current control comparator 72
`which may comprise a circuit sold under the numerical
`designation 5556 by Signetics Corporation compares In
`with I R. If In becomes less than IR, the comparator 72
`initiates the generation of a pulse by a pulse generator
`114 which may comprise a circuit sold under the desig-
`nation CD4OI 1 by Radio Corporation of America. The
`resulting pulse generated by the generator 114 causes
`the sequence counter 88 which may comprise a Circuit
`sold under the designation CD4017 by Radio Corpora—
`tion ofAmerica to sequence to the next step and cause
`discharge of one of the capacitors 26. Each time In
`starts to fall below IR as determined by the comparator
`72. a pulse is provided by the pulse generator 114 to
`step the sequence counter 88 to the next position and
`cause discharge of another one of the capacitors 26.
`Accordingly, current delivered to the patient is com-
`pletely independent of the patient’s body resistance or
`variations thereof. The current actually delivered to the
`patient is monitored and is compared with a reference
`value to insure it is maintained at or slightly above the
`reference value through the sequential discharge of the
`capacitors 26.
`As previously noted, a representation of the deliv—
`ered current I" is provided by the lead 110 to the cur-
`rent amplifier 112. At the same time. the actual voltage
`across the patient at
`the electrodes 98 and 100 is
`sensed, then amplified by a voltage amplifier 120. The
`voltage is amplified in the amplifier 120 to provide a
`voltage V to a multiplier 122. A current I as amplified
`by the Current amplifier 112 in response to in is also
`provided to the multiplier 122. The multiplier 122 cf-
`fectively multiplies I by V to provide a representation
`of the actual power delivered to the patient. This repre—
`sentation is integrated with respect to time in an inte-
`grator 124 to provide a representation of delivered en-
`ergy ED. The current amplifier 112, the voltage ampli—
`fier 120 and the multiplier 122 may together comprise
`a circuit sold under the designation MC 1 595 by Motor~
`Ola Radio Corporation. The integrator 124 may come
`prise a circuit sold under the designation N5556 by Sig-
`netics Corporation. The signal representing the deliv—
`ered energy E» is applied to the comparator 78 as well
`as to the energy display 80 to provide a visual display
`of the energy actually being delivered to the patient.
`The comparator 78 which may comprise a Circuit
`sold under the numerical designation 5556 by Signetics
`Corporation compares the delivered energy ED with the
`selected or reference energy E". When ED becomes
`equal to ER, indicating that the desired amount of en-
`ergy has been delivered, the comparator 78 provides a
`pulse via a lead 126 to the sequence counter 88 and to
`a silicon controlled rectifier 128 comprising the SCR
`truncate circuit 42. The pulse fires
`the silicon-
`controlled rectifier 128 to provide a temporary shunt
`path bypassing the patient. This rapidly terminates the
`current pulse as seen in FIG. 3. At the same time, the
`pulse from the comparator 78 causes the sequence
`counter 88 to sequence through all remaining positions
`so as to discharge all of the capacitors 26 not yet dis-
`charged. This is a safety feature which prevents inad—
`vertent delivery of an unwanted current pulse to a pa-
`tient at a later time.
`Accordingly. the energy computer 40 responds to the
`actual delivered current and voltage at the patient and
`computes the delivered energy 13,, during each current
`pulse. The control circuit 32 and the SCR truncate cir—
`
`’Jt
`
`lo
`
`20
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`cuit 42 in turn respond when ED is equal to the desired
`energy E" by truncating or shunting the current pulse
`away from the patient while at the same time insuring
`that all capacitors are discharged.
`It has been found that when a nominal current IR of
`approximately 20 amperes is selected, the duration of
`the current pulse is typically on the order of about
`l0
`milliseconds so as to supply an amount of energy typi-
`cally selected. The particular circuit of FIG. 4 has been
`found to provide a rise time in the current pulse in the
`order of 100 microseconds and a fall time on the order
`of 10 microseconds.
`Use of plural capacitors in accordance with the in-
`vention provides for a defibrillator which is very coma
`pact and light in weight. A portable defibrillator utiliz—
`ing the circuit of FIG. 4 weighs approximately l5
`pounds compared with weights on the order of 30
`pounds and greater in most prior art defibrillators. In
`the particular circuit of FIG 4. the delivered energy is
`continuously adjustable up to 300 watt—seconds, the de-
`livered current is made adjustable up to 40 amperes so
`as to maintain a constant current independent of the
`patient’s skin impedance over a range of 30 to I20
`ohms, and a peak delivered voltage of 3 kilovolts is
`made available. The 10 D size batteries used will last
`through at
`least 50 different 300 watt~second dis-
`charges before requiring recharging.
`While the invention has been particularly shown and
`described with reference to a preferred embodiment
`thereof, it will be understood by those skilled in the art
`that various changes in form and details may be made
`therein without departing from the spirit and scope of
`the invention.
`What is claimed is:
`1. A defibrillator for delivering electrical current to
`a plurality of patient electrodes comprising:
`a plurality of electrodes;
`a plurality of capacitors coupled to the electrodes;
`means coupled to the capacitors and including a
`power source for charging the capacitors;
`means coupled to the capacitors for initiating dis-
`charge of at least one of the capacitors to initiate
`generation of a current pulse; and
`means coupled to the capacitors and responsive to
`the initiating of discharge of at least one of the ca—
`pacitors for subsequently discharging at least one
`other capacitor during the discharge of said at least
`one of the capacitors to continue the generation of
`the current pulse.
`2. The invention defined in claim 1, wherein the
`means for subsequently discharging at least one other
`capacitor during the discharge cycle comprises means
`for initiating discharge of said at least one other capaci—
`tor When the magnitude of the current pulse as pro-
`vided by discharge of said at least one of the capacitors
`decreases to a predetermined minimum value.
`3. The invention defined in claim 1, further including
`means for monitoring delivered electrical energy at the
`electrodes, a shunt lead coupled in parallel with the
`electrodes and means coupled to the monitoring means
`for discharging all capacitors not already discharged
`through the shunt lead whenever the delivered electri—
`cal energy reaches a selected value.
`4. A defibrillator for delivering electrical current to
`a plurality of patient electrodes comprising:
`a plurality of electrodes;
`a plurality of capacitors coupled to the electrodes;
`
`7
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`3,886,950
`
`10
`
`tude;
`means for comparing the measured magnitude of the
`current pulse with the desired value of current
`magnitude to provide a current error signal repre-
`senting the difference therebetween;
`means responsive to the current error signal and cou-
`pled to the capacitors for selectively discharging
`the capacitors in accordance with the value of the
`current error signal to maintain the magnitude of
`the current pulse substantially equal to the desired
`value of current magnitude;
`means for measuring the electrical energy delivered
`to the patient via the current pulse;
`means for comparing the measured electrical energy
`with the desired value of energy to provide a pulse
`termination signal whenever the measured electri-
`cal energy is substantially equal
`to the desired
`value of energy; and
`means responsive to the pulse termination signal for
`terminating the current pulse at the electrodes.
`8. The invention defined in' claim 7, wherein the
`means for selectively discharging the capacitors in-
`cludes a plurality of silicon controlled rectifiers, means
`for coupling each of the silicon controlled rectifiers be-
`tween a different one of the capacitors and one of the
`electrodes, and means for selectively gating each of the
`silicon controlled rectifiers.
`9. The invention defined in claim 8, further including
`a plurality of serially coupled diodes coupled between
`the electrodes, and wherein each of the capacitors is
`coupled in parallel w