US3258013A

US3258013A - Defibrillators

Info

Publication number: US3258013A
Application number: US291703A
Authority: US
Inventors: Walter S Druz
Original assignee: Zenith Radio Corp
Current assignee: Zenith Electronics LLC
Priority date: 1963-07-01
Filing date: 1963-07-01
Publication date: 1966-06-28
Anticipated expiration: 1983-06-28
Also published as: FR1408284A; NL6407408A; GB1037117A; DE1439985A1

Description

W. s. DRUZ DEFIBRILLATORS June 28, 1966 2 Sheets-Sheet 1 Filed July 1, 1963 ow R 9 6.170 E9310 \K m Mat Ll AW 9am m 9 $5.2m w W d N W i 4M m r Qm m a WPW aw mm R w mm w? i June 28, 1966 w. s. DRUZ 3,258,013

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I.- E E w DEFIBRILLATION g DEFIBRILLATION f; THRESHOLD 3 THRESHOLD 3 O O 0 2 4 6 1 Time (ms) (ms) -DEFIBRILLAT|ON DEFIBRILLATION |NTERVAL INTERVAL U) S OIOOO Ioo OHM LOAD IL 1: a 3 21 I. 5001 Zr1 50 OHM LOAD E Q E INVENTOR.

o 25 so TIME-MILLISECONDS W617 fez" fl Drag I United States Patent 3,258,013 DEFIBRHLLATORS Walter S. Druz, Bensc'uville, iii, assignor to Zenith Radio Corporation, Chicago, Ill, a corporation of Delaware Filed July 1, 1%3, Ser. No. 291,703 14 Claims. (Cl. 1284l9) This invention is directed to medical electronic devices and more specifically to electrical defibrillators for use in terminating heart fibrillations of a living organism, and particularly for defibrillating the human heart.

Fibrillation, or uncontrolled and arhythmic expansion and contraction of various groups of heart muscles, is a condition which may be induced by accidental electric shock or under other conditions of severe stress as in the course of surgical operations, heart attacks, drowning, or the like. When encountered, prompt and effective counter-measures must be taken if the organism is to survive. As an emergency measure, rhythmic compression of the heart by a technique resembling artificial respiration may be employed, but this is a temporary or stop-gap measure and by itself is ineffective in many instances.

It is well known that defibrillation may be achieved by the applicatiton of a controlled electric shock. For this purpose, several types of electrical equipment have been devised. Historically, the earliest type of electrical defibrillator successfully employed on a human was a unit which delivered an alternating current burst of approximately one-quarter second duration and with an R.M.S. voltage of from 110 to 220 volts to an exposed heart following thoracectomy. Subsequent studies established that defibrillation by alternating current shock may be effected through the closed chest provide-d sufficient voltage and therefore current is available. The minimum alternating current necessary to provoke generalized intense contraction of the myocardium has been shown to be about one ampere for the exposed heart and about three amperes for the closed chest, the body resistances encountered averaging 50 ohms and 90 ohms respectively. Alternating currents smaller than one ampere will frequently throw a normal heart into fibrillation instead of a generalized contraction; obviously, the effect of an alternating current on the myocardium is excitation and not inhibition. Thus, suflicient current density per unit of weight of myocardium is essential to successful ventricular defibrillation. In practice, it has been found that successful defibrillation by the applicatiton of the recommended one-quarter second alternating current shock is invariably accompanied by excessive tissue heat generation with resultant thermal damage to the myocardium and, in closed chest application, to the thoracic Wall. Moreover, the power source required to generate alternating current at the required voltage is sufiiciently large and cumbersome as to substantially and practically confine the utility of A.C. defibrillators to permanent hospital installations.

In an effort to substantially reduce the collateral tissue damage attendant upon use of an A.C. defibrillator, apparatus has been developed for employing a direct-current capacitor discharge to achieve defibrillation. Still another form of DC actuated defibrillating equipment which has been devised and experimentally employed develops a defibrillation impulse by condenser discharge through an iron core choke or other inductance. While 3,25%,fil3 Patented June 28, 1966 the use of impulses of these types have been successfully employed to achieve defibrillation, myocardial damage has been encountered as in the use of A.C. apparatus, although to a somewhat lesser extent. Additionally, because such equipment delivers substantial energy at reduced voltages after termination of the defibrillating interval, refibrillation has been encountered in some cases. Moreover, although a DC. source is employed to charge the storage condenser, the power requirements of previously known equipment have all been so high as to render the construction of a truly portable battery-operated defibrillating apparatus infeasible.

As an additional limitation upon previously developed 'defibrillating equipment, it should be borne in mind that defibrillators may be employed either in the open chest condition following thoracectomy, or transthoracically through the closed chest. The human body resistance in the former case is approximately 50 ohms, while in the latter condition the body resistance is approximately to ohms. Because of this substantial variation in body resistance, and to provide for adjustability of'the energy delivered in an effort to minimize collateral tissue damage, previously developed A.C. and DC. defibrillators have been provided with adjustable operating controls which must be preset for each individual use of the equipment, depending on the nature of the case. More particularly, previous A.C. and DC. defibrillators have required different settings of the operating controls for use in closed chest and exposed heart defibrillation respectively.

It is a primary object of the present invention to provide a new and improved electrical defibrillator in which one or more of the major disadvantages of previous electrical defibrillators are obviated.

A more specific object of the invention is to provide a new and improved defibrillator which is highly effective in terminating fibrillation of the heart of a living organism, and particularly in defibrillating the human heart, Without accompanying substantial thermal damage to the myocardium or to the thoracic wall.

Still another object of the invention is to provide a battery-operated electrical defibrillator which is sufficiently compact and light-weight as to be useful as a portable unit for emergency on-the-site use.

Yet another object of the invention is to provide a new and improved universal electrical defibrillator which may be employed for either exposed heart or closed chest defibrillation without resetting of any primary operating controls.

In accordance with the present invention, a new and improved electrical defibrillator comprises a delay line discharge pulsing circuit having at least two inductancecapacitance sections for producing a single direct-current output pulse having a substantially trapezoidal waveshape. Means are provided for storing a predetermined amount of energy in the delay line discharge pulsing circult, and a pair of electrodes are coupled to the delay line discharge pulsing circuit and adapted to be applied to the body of a living organism at spaced locations on opposite sides of the heart for discharging at least a portion of the stored energy through the heart in the form of a single direct current output pulse of substantially trapezoidal waveshape.

In accordance with another aspect of the invention, an electrical defibrillator operable from a wholly self-contained battery power source comprises means including an inverter and a rectifier coupled to the battery for converting direct current from the battery to alternating current at a higher voltage and rectifying the alternating current to provide direct current at a higher voltage than that of the battery power source. Charge storage means are coupled to the previously identified means and responsive to the higher-voltage direct current to store electrical charge at a predetermined level required to deliver a defibrillating impulse upon discharge of the charge storage means through the body of a living organism. Sensing means are coupled to the charge storage means for developing a control effect proportional to the charge stored in the charge storage means, and a transistorized control circuit is coupled to the sensing means and to the first-mentioned means and responsive to the control effect for actuating the first-mentioned means to maintain the stored charge at the predetermined level.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood, however, by reference to the following description taken in connection with the accompanying drawings, in the several figures of which like reference numerals indicate like elements, and in which:

FIGURE 1 is a schematic circuit diagram of an electrical defibrillator embodying the present invention;

FIGURES 2a, 2b and 2c are graphical representations of the wave forms of defibrillating impulses delivered by prior art defibrillators;

FIGURE 2d is a similar graphical representation illustrating the waveform of the defibrillating impulse delivered by the defibrillator of FIGURE 1; and

FIGURE 3 is a graphical representation illustrating the automatic variation in the defibrillating impulse delivered by the apparatus of FIGURE 1, depending upon whether the unit is employed in an exposed heart or a closed chest application.

The defibrillator of FIGURE 1, which constitutes a preferred embodiment of the present invention, comprises a transistorized inverter 12 for converting direct current from a self-contained battery to alternating current which is stepped up to a higher voltage by stepup transformer 13 and applied to a rectifier 14 to supply direct current at a higher voltage than that of battery 1t). The direct current output of rectifier 14 is applied to a delay line discharge pulsing circuit 15 which in turn is coupled to a pair of electrodes 16 and 17 adapted to be applied to the body of a living organism at spaced locations on opposite sides of the heart for discharging at least a portion of the energy stored in delay line discharge pulsing circuit 15 through the heart. A transistorized control circuit 18 is provided for actuating the electronic charging current supply means 12, 13, 14 to maintain the charge stored in delay line discharge pulsing circuit 15 at a predetermined level required to deliver a defibrillating impulse on being discharged through the body of a living organism by means of electrodes 16 and 17. Transistorized control circuit 18 is responsive to a control effect derived by sensing the charge stored in delay line discharge pulsing circiut 15 in a manner to the described. The entire system is operable from a wholly self-contained battery power source 10 which may constitute a conventional l2-volt, 4-ampere hour storage battery; if desired, the apparatus may be provided with a battery charger 11 adapted to be connected to battery 10 by means of a switch 19 for recharging during intervals when the defibrillator is not in use.

More specifically, inverter 12 includes a conventional transistor-operated square wave oscillator 20 which is energized from battery 10 to develop a 400-cycle alternating voltage across the primary winding 21a of a transformer 21. The operating potential connection from battery 10 to square wave oscillator 20 is provided by a lead 22 from the positive terminal of battery 10 to a center tap on primary winding 21a, as shown. The secondary winding 21b of transformer 21 is coupled to the base electrodes of a pair of

pnp transistors

23 and 24 by means of a pair of series connected

biasing resistors

25 and 26. A center tap on secondary winding 21b is coupled to the emitter electrodes of

transistors

23 and 24 through the parallel combination of a resistor 27 and a condenser 28, which in turn are connected across the normally open contacts 29 of a relay having an operating coil 30 which is included in transistorized control circuit 18, to be described.

The collector electrodes of

transistors

23 and 24 are connected to opposite terminals of the primary winding 13a of step-up transformer 13, and a center tap 31a on primary winding 13a is connected to the negative terminal of battery 10. The secondary winding 13b of transformer 13 is connected to a pair of diagonally opposite input terminals of a bridge type rectifier 14 comprising

silicon diodes

14a, 14b, 14c and 14d connected in the respective legs of the bridge network in conventional fashion. The negative-polarity output terminals of bridge rectifier 14 is connected to electrode 16, and the positivepolarity output terminal of rectifier 14 is connected to a fixed contact 31 of a relay having an operating winding 32 and an armature 33 which is normally in engagement with fixed contact 31. Armature 33 is connected to delay line discharge pulsing circuit 15 which in the illustrated embodiment comprises a two-section lumped constant delay line with

series inductors

34 and 35 and

shunt condensers

36 and 37, as shown.

Inductors

34 and 35 are also coupled by mutual inductance between their respective windings, as indicated by the legend M in the drawing. Upon energization of operating coil 32, in a manner to be described, armature 33 is caused to engage an additional fixed contact 38 connected to output electrode 17. Operating winding 32 is connected across battery 10 through a pair of series-connected normally open switches 39 and 40, the actuating members of which are conveniently positioned in insulating

handles

41 and 42 attached to electrodes 16 and 17, as schematically indicated by the dotted lines in the drawing.

The transistorized control circuit 18 is also shown in schematic detail in FIGURE 1. The upper terminal of primary winding 21a of transformer 21 is connected to the anode of a solid-state diode rectifier 43, the cathode of which is connected to the center tap of secondary winding 21b through a resistor 44, and is also bypassed to the center tap of primary winding 21a by a filter condenser 45.

The positive terminal of battery v10 is coupled to the collector electrode 46 of a first npn control transistor 47 through a pair of series-connected

resistors

48 and 49. The emitter 50 of transistor 47 is connected to the negative terminal of battery 10 through switch 19. A Zener diode 51 is connected between emitter 50 and the junction of

resistors

48 and 49. A resistor 52 and a potentiometer resistor 53 are connected in series across Zener diode 51, and the movable tap 54 of potentiometer resistor 53 is connected to the base electrode 55 of transistor 47. Base electrode 55 is also connected to the junction between a pair of series-connected

resistors

56 and 57 which in turn are connected between the positive output terminal of rectifier 14 and, through switch 19, the negative terminal of battery 10.

Collector 46 of first control transistor 47 is directly connected to the base electrode 58 of a second npn control transistor 59. The emitter electrode 60 of transistor 59 is connected through a resistor 61 and switch 19 to the negative terminal of battery 10. Emitter 60 is also connected to the center tap of secondary winding 21b of transformer 21 through the parallel combination of a resistor 62 and a condenser 63. The collector electrode 64 of control transistor 59 is connected through operating coil 30 of

relay

29, 30 of

relay

32, 33 to the positive terminal of battery A voltmeter 65 and a resistor 66 are connected in series between electrode 16 and armature 33 of

relay

32, 33.

In normal operation, battery-charger 11 is disconnected and switch 19 is operated to the illustrated position to connect battery 10 in the circuit. In this condition, the entire unit is readily portable and may be employed for on-site emergency use without the necessity of connecting the apparatus to the alternating-current supply mains or other auxiliary source of operating power.

Square wave oscillator 20 may be of conventional transistorized construction to generate an alternating current output voltage of square or rectangular wave form at a frequency of about 400 cycles per second. This voltage is impressed through transformer 21 on the base electrodes of

transistors

23 and 24 which are connected as a push-pull power amplifier. The amplified alternating current output from

transistors

23 and 24 is stepped up in voltage by transformer 13 and impressed on bridge rectifier 14. The resulting rectified direct current output is employed to charge the

storage condensers

36 and 37 of delay line discharge pulsing circuit 15.

Transistorized control circuit 118 is provided for the purpose of regulating the energy stored by delay line discharge pulsing circuit 15. To facilitate an understanding of the operation of control circuit 18, it may be assumed that the delay line discharge pulsing circuit has been fully charged to the desired voltage, and that in this condition relay contacts 29 are open as depicted in the drawing. A positive bias potential, more strongly positive than the voltage of battery ltl, is developed by diode 43 which rectifies a portion of the 400-cycle per second alternating voltage developed across the upper half of primary winding 21a. This auxiliary bias potential is filtered by resistor 44 and condenser 45 and is impressed on the center tap of secondary winding 21b. With contacts 29 open as shown, the strongly positive auxiliary bias potential, designated in the drawing, is impressed on the base electrodes of

transistors

23 and 24 to render them non-conductive; consequently the charging voltage for delay line discharge pulsing circuit 15 is interrupted.

Control transistor 47, in this condition of the circuit, is biased to be fully conducting, while second control transistor 59 is maintained in the non-conductive state. To this end, the positive voltage of battery 1th is impressed across the voltage divider consisting of

resistors

48 and 52 and potentiometer 53'. Zener diode 51 is provided to stabilize the voltage drop across the series combination of resistor 52 and potentiometer 53. Accordingly, base electrode 55 is normally maintained at a positive potential, to maintain grounded-emitter npn transistor 47 fully conductive.

Resistors

62 and 61 are proportioned to maintain a sufiiciently strong positive bias on emitter 60 to maintain npn transistor 59 non-conductive when transistor 47 is in the fully conductive condition described.

With delay line discharge pulsing circuit 15 in the fully charged condition and with relay contact 29 open as shown, the voltage across the delay line is indicated visually by voltmeter 65 and is also impressed across the voltage divider consisting of

resistors

56 and 57 which are proportioned to maintain npn transistor 47 in the fully conductive state under the full-charge condition of delay line 15. However, as charge leaks off from

storage condensers

36 and 37, the terminal voltage of the delay line discharge pulsing circuit 15 drops proportionately. A corresponding control effect is developed across resistor 56, and this reduces the potential applied to base electrode 55 of control transistor 47 from the junction between

resistors

56 and 57. This results in negative current through base electrode 55, and being a currentresponsive device, transistor 47 is rendered non-conductive when the comparison voltage derived from delay line 15 has fallen by an amount determined by the setting of movable tap 54 on potentiometer 53.

and through operating coil 3-2 When transistor 47 becomes non-conductive, the voltage at collector 46 increases and is applied to base electrode 58 to render transistor 59 conductive, thus establishing collector current flow through operating coil 30 and closing relay contacts 29 to restore the charging circuit for delay line discharge pulsing circuit 15 by removing the cut-oft bias from the base electrodes of

transistors

23 and 24; the current flow in coil 30 is insufiicient to operate

relay

32, 33. At the same time, the positive potential applied to emitter 69 of control transistor 59 is reduced because closing of contacts 29 drops the voltage across

divider

62, 61 from the auxiliary biasing potential to the battery potential This lowers the base voltage cut-off threshold of transistor 59 and prevents chattering of relay contact 29. When the charge on delay line discharge pulsing circuit 15 has been restored to the preset level determined by the setting of movable tap 54 on potentiometer 53, the resulting reduction in negative base current for transistor 47 re establishes transistor 47 in its conductive state, cutting oif transistor 59 and dropping out relay contact 29 to restore transistorized control circuit 18 to its reference condition.

In closed-chest utilization of the defibrillator of FIG- URE l, electrode 16 is placed on the right border of the sternum just below the sternal notch, while electrode 17 is placed on the left midclavicular line near the fifth interspace, with the heart approximately midway between. For internal use, following thoracectomy, the electrodes may be applied directly across the heart. Upon ascertaining by visual observation of voltmeter 65 that the stored energy across delay line discharge pulsing circuit 15 is at the requisite level determined by the attending physician, switches 39 and 46 are closed to discharge delay line 15 through the heart to accomplish defibrillation. Upon termination of the defibrillating impulse, switches 39 and 40 are released to restore the apparatus to its normal charging condition. It will be observed that switches 39 and ll when closed substantially short out relay coil 30, preventing recharging of pulse circuit 15 prior to release of at least one of switches 39 and it).

An appreciation of the types of defibrillating impulses delivered by previously employed devices, and their effects on the patient, is important to facilitate a full appreciation of the present invention. FIGURE 2a graphically illustrates the waveform of the defibrillatory current delivered by a conventional alternating current defibrillator, the impressed current being plotted as a function of time. To provoke generalized intense contraction of the myocardiurn, in the exposed heart application, the minimum alternating current has been experimentally determined to be approximately one ampere for a recommended period of one'quarter second. For transthoracic defibrillation, the minimum current required is approximately 3 amperes for the same time duration. The characteristic body impedance encountered is, for the human body, approximately 50 ohms for the exposed heart and ohms in closed chest application and is resistive. Thus, especially for closed chest application, the applied energy required for successful ventricular defibrillation is very substantial indeed and has been found to result insubstantial heat damage to the myocardium and the thoracic wall. For example, a current of 5 amperes across a closed chest resistance of 90 ohms generates heat equivalent to 2250 watts which, over the one-quarter second defibrillation interval, corresponds to an integrated energy of 5 62 watt-seconds.

FIGURE 2b illustrates the waveform of the defibril latory current impulse delivered by a DC. capacitor discharge type of defibrillator. It is known that the defibrillatory effectiveness of a capacitor discharge depends on the stored energy of the condenser, which in turn is equivalent to one-half the capacitance times the voltage squared. Previous work in the field has established that, with a direct current defibrillatory impulse, myocardial damage is more dependent on the peak voltage than the total energy supplied, and that the defibrillation threshold voltage decreases exponentially with increased capacitance, approaching asymtotically a limiting value of approximately one and one-half kilovolts. Moreover, a minimum or threshold current must be exceeded for a required period of time in order to effect ventricular defibrillation, and impressed electric currents below the defibrillation threshold, and particularly currents smaller than one ampere, have been found to frequently throw a normal heart into fibrillation. It is apparent from examining the waveform of FIGURE 21) that with a simple capacitor discharge, a peak current substantially above the defibrillation threshold must be applied in order to maintain the defibrillating current above the threshold for the required defibrillation interval. In other words, the duty cycle of the applied defibrillating impulse as shown in FIGURE 2b, which may be defined as the ratio of the integrated area under the current-time characteristic within the defibrillation interval to the total currenttime integral, is limited to approximately 50%. Moreover, the energy applied at currents below the defibrillation threshold, represented by the shaded area under the waveform of FIGURE 21), as well as the steep initial slope of the defibrillating impulse, have been found to be detrimental both from the point of view of myocardial damage and re-inducement of a fibrillatory state.

Myocardial and thoracic wall heat damage may be reduced by discharging the storage condenser through an inductance to produce the defibrillation impulse graphically represented in FIGURE 2c. As is apparent by comparing FIGURE and FIGURE 2b, this has the effect of reducing the steepness of the defibrillatory impulse wavefront as well as the peak current required to maintain a sustained current level above the defibrillation threshold for the required defibrillation interval. However, the duty cycle obtainable in this manner is even smaller than that which may be achieved with a simple capacitor discharge, by virtue of the damped oscillatory character of the defibrillating impulse.

The defibrillation impulse produced by a device constructed in accordance with the present invention is graphically represented in FIGURE 20!. In accordance with the invention, a delay line discharge pulsing circuit is employed as the energy storage device, with at least two inductance-capacitance sections as shown in FIGURE 1, and proportioned to have a characteristic impedance substantially matching that encountered upon applying the electrode 16 and 17 to the body of the patient. In this manner, a defibrillatory impulse having a substantially trapezoidal waveform as shown in FIGURE 2d is attained, with a duty cycle in excess of 80% and a peak current or-peak energy above the defibrillation threshold of less than To insure successful ventricular defibrillation, it has been found that this type of defibrillating current should be maintained above the defibrillating threshold for a defibrillation interval of at least 8 milliseconds.

In practice, it has been found that a D.C. monopulse defibrillator embodying the present invention should preferably have a delay line discharge pulsing circuit with a characteristic impedance of approximately 100 ohms and should deliver a current impulse corresponding to an energy of from to 100 watt-seconds at a generator voltage, considering the generator to be in series with its source impedance, of from 1500 to 2500 volts thereby resulting in a voltage of from 750 to 1250 volts being applied across the terminating impedance, i.e., the body of the patient. A closer approximation of a trapezoidal waveform may be achieved by increasing the number of inductance-capacitance sections of delay line 15, but experimental results to date have established that the waveform provided by a. two-section line as shown is a sufficiently close approximation to achieve the utmost in reliability without accompanying tissue damage to the myocardium or the thoracic wall.

In a preferred embodiment of the invention, a twosection inductance-capacitance delay line discharge pulsing circuit 15 having the following component characteristics has been employed with eminent success:

Capacitors 36 and 37-20 microfarads each Inductors 34 and 35l50 millihenries each, with 17 ohms internal resistance each Mutual inductance between inductors 34 and 3550 millihenries Total inductance of discharge of delay line discharge pulsing circuit 15400 millihenries Such a delay line discharge pulsing circuit has a characteristric impedance of approximately 100 ohms, which substantially matches the characteristic impedance of the human body for transthoracic applications. The defibrillatory impulse delivered by this preferred embodiment of the invention is characterized, for transthoracic application, by a duty cycle of with a defibrillation threshold of 6.5 amperes and a peak current of 10 amperes for a defibrillation interval of 8.5 milliseconds. The tissuedamaging effects attributable to the steep wavefront characteristic of a simple capacitor discharge and to the application of substantial energy at current levels below the defibrillation threshold are substantially avoided, as has been verified by experimental use of the equipment.

In accordance with another aspect of the invention, the defibrillator in its preferred embodiment of FIGURE 1 constitutes a universal apparatus for delivering defibrillatory energy above a predetermined defibrillation threshold for use in either a transthoracic or exposed-heart defibrillation. As pointed out above, the characteristic impedance of delay line discharge pulsing circuit 15 is preferably approximately 100 ohms, which substantially matches the characteristic impedance between the spaced locations on the body of the patient to which electrodes 16 and 17 are applied for transthoracic defibrillation. In exposed-heart applications, following thoracectomy, when electrodes 15 and 17 are placed directly across the heart, the body impedance encountered is approximately 50 ohms, substantially resistive. Thus, in exposed-heart ap plications, delay line discharge pulsing circuit 15 is terminated in an impedance mismatch, causing reflections and thereby reducing the voltage of the applied defibrillatory impulse to maintain the current through the heart at approximately the same level as that achieved with transthoracic applications. In other words, the peak voltage of the delivered pulse is automatically adjusted to maintain a substantially constant current level for either closed chest or open chest application. Accordingly, the apparatus of FIGURE 1 may be employed in either type of application without the necessity of readjusting any circuit component. While potentiometer 53 is provided for the purpose of permitting adjustment of the defibrillatory pulse voltage, such adjustability is not an essential feature of the apparatus; fixed circuit elements may readily be substituted, if properly proportioned to provide the required output pulse characteristics for closedchest application, and the apparatus will automatically be in proper adjustment for open-chest use.

This feature of the invention may be more readily appreciated by consideration of the graphical representation of FIGURE 3, in which the voltage of the defibrillatory impulse is plotted as a function of time for both closedchest and open-chest applications. Waveform A illustrates the defibrillation impulse delivered between electrodes 16 and 17 in transthoracic use, and corresponds substantially to the waveform of FIGURE 2d. In exposed-heart use, the defibrillation impulse is that depicted as curve B in FIGURE 3, with the peak voltage falling by approximately one-half as a result of impedance mismatch caused by reduction of the load impedance from or ohms to 50 ohms. While the impedance mismatch introduces a small amount of damped oscillatory energy at the termination of the defibrillating impulse, the duty cycle is still at least 80% and the peak energy delivered is above but less than 50% greater than the defibrillation threshold. Thus, in both types of application, a single defibrillating impulse of substantially trapezoidal waveform, with optimum defibrillating characteristics, is delivered.

The monopulse D.C. defibrillator of the present invention has been extensively evaluated by experimentation with artifically induced fibrillation in dogs, both by transthoracically applied electric shock (100 milliamperes alternating current for from 1 to 6 seconds) and by ligation of the circumflex and anterior descending coronary arteries. Defibrillation effectiveness of the DC. monopulse unit of the present invention was also compared with that of a standard A.C. defibrillator unit.

In the series of dogs where fibrillation was effected with a small-magnitude alternating current, and the heart allowed to fibrillate for a two-minute period, defibrillation was successful but resuscitation was found to be impossible. Apparently a two-minute period of myocardial and brain hypoxia was not conducive to successful resuscitation.

In another series of dogs, ventricular fibrillation was artificially induced and immediately defibrillated, while in a third series an interval of one minute between fibrillation and defibrillation was permitted. The differences in electrocardiographic and cardiovascular responses were minimal for either A.C. or DC. defibrillation, but the differences in response between D.C. defibrillated and A.C. defibrillated animals became very manifest. The A.C. defibrillating current is definitely more toxic, not only to the heart but to the animal as a whole. After an AC. defibrillating shock of 480 volts, it was not uncommon to find runs of ventricular extra-systoles, a depressed ST segment, an inverted T-wave (signs of myocardial ischemia or infarction) and, wit-h more frequent repetition of the fibrillation-defibrillation sequence, atrial fibrillation. Such severe symptoms were not encountered with the DC. de-fibrillating impulse of 80 watt-seconds, although depressed S-T segments and sinus tachycardia were sometimes encountered. The blood pressure response to the A.C. defibrillating current was Very similar to a rapid intravenous injection of at least one milligram of epinephrine with a time lag of from one-half to one second before resumption of heartbeat and effective blood pressure restoration, frequently making it difiicult to determine whether defibrillation was effective or not. In contrast, the DC. impulse immediately causes a contraction and an effective blood pressure response (if a response is forthcoming). The side effects on the whole animal, frequently encountered with A.C. defibrillation, such as excessive salivation, severe muscular contractions, defecation and urination were rarely encountered with DC. defibrillated animals. Analogous results were obtained with animals in which ventricular fibrillation was induced by ligation of coronary arteries, an experimental situation which in many ways approximates that of a patient who suddenly develops a myocardial infarct.

The DC. monopulse defibrillator of the present invention has also been given extensive experimental use on human patients in hospital installations. In some instances, defibrillation has been successfully achieved after failure of an A.C. defibrillator. Experience to date has indicated that defibrillation is invariably achieved with the application of a single impulse, and without encountering refibrillation r myocardial or thoracic wall heat damage. As a result of the highly efficient solid-state switching circuitry, a large peak current can be supplied to effect charging or recharging of the battery in as little as 3 seconds; even with an almost totally discharged battery, the charging time for delay line discharge pulsing circuit 15 does not exceed 4 or 5 seconds.

Transistorized control circuit 18 maintains a nearly constant charge on the capacitors and keeps the equipment ready for immediate use, and this is accomplished with minimum strain on the self-contained battery. The entire unit is completely portable and weighs only 38 pounds, including a battery charger for recharging the 12 volt, 4- ampere hour battery which supplies s-ufiicient operating power to deliver several hundred defibrillating impulses without recharging.

While a particular embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that change-s and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. A direct-current rnonopulse electrical defibrillator comprising:

a delay line discharge pulsing circuit having at least two inductance-capacitance sections for producing on discharge a single direct-current output pulse having a substantially trapezoidal waveshape;

means for storing a predetermined amount of energy in said delay line discharge pulsing circuit;

and means, including a pair of electrodes coupled to said delay line discharge 'pulsin circuit and adapted to be applied to the body of a living organism at spaced locations on opposite sides of the heart, actuatable subsequent to the storage of said energy for discharging from said pulsing circuit through said heart at least a portion of said energy as only a single such pulse for each actuation in the form of said single direct current output pulse of substantially trapezoidal waveshape.

2. A direct-current moncpulse electrical defibrillator comprising:

a pair of electrodes adapted to be applied to the body of a living organism at spaced locations on opposite sides of the heart;

a delay line discharge pulsing circuit coupled to said electrodes and having at least two inductance-capacitance sections and further having a characteristic impedance substantially matching that between said spaced locations of said body for producing on discharge a single direct current output pulse having a substantially trapezoidal waveshape;

and means, including a direct-current source, for storing a predetermined amount of energy in said delay line discharge pulsing circuit and actuatable subsequent to the storage of said energy for discharging on each actuation only a single substantially trapezoidal direct-current output pulse from said circuit through said heart upon application of said electrodes to said body at said spaced locations.

3. A defibrillator according :to claim 2 in which said characteristic lmepdance is substantially 100 ohm-s and said predetermined amount of energy is from 60 to 100 watt-seconds at a generator voltage of from 1500 to 2500 volts.

4. An electrical defibrillator for delivering electrical energy above a predetermined defibrillation threshold for use in terminating heart fibrillation comprising:

a source of direct current;

and means, including a delay line discharge pulsing circuit having at least two inductance-capacitance sections, coupled to said direct-current source and to said electrodes and actuatable to deliver through said electrodes, when applied to said body, only a single substantially trapezoidal pulse of direct current electrical energy for each actuation, said pulse having a peak amplitude above but less than 50% greater than said defibrillation threshold and a duty cycle in excess of 5. An electrical defibrillator for delivering electrical energy above a predetermined defibrillation threshold for use in terminating heart fibrillation comprising:

a source of direct current;

and means, including a delay line discharge pulsing circuit having at least two inductance-capacitance sections and having a characteristic impedance substantially matching that between said spaced locations of said body, coupled to said direct-current source and to said electrodes and actuatable to deliver through said electrodes, when applied to said body, only a single substantially trapezoidal puls of direct current electrical energy for each actuation, said pulse having a peak amplitude less than 50% above said defibrillation threshold and a duty cycle in excess of 80%.

6. An electrical defibrillator for delivering electrical energy above a predetermined defibrillation threshold for use in terminating heart fibrillation comprising:

a source of direct current;

and means, including a delay line having at least two inductance-capacitance sections and having a characteristic impedance substantially matching that between said spaced locations of said body, coupled to said direct current source and to said electrodes and actuatable to deliver through said electrodes, when applied to said body, only a single substantially trapezoidal pulse of direct current electrical energy for each actuation, said pulse being of at least milliseconds duration and having a peak amplitud above but less than 50% greater than said defibrillation threshold.

7. An electrical defibrillator for delivering electrical energy above a predetermined defibrillation threshold for use in terminating heart fibrillation comprising:

a source of direct current;

and means, including a delay line having at least two inductance-capacitance sections and having a characteristic impedance substantially matching that between said spaced location of said body, coupled to said direct-current source and to said electrodes and actuatable to deliver through said electrodes, when applied to said body, only a single substantially trapezoidal pulse of direct-current electrical energy for each actuation, said pulse being of at least 10 milliseconds duration and having a peak amplitude less than 50% above said defibrillation threshold and a duty cycle in excess of 80%.

8. An electrical defibrillator for delivering electrical energy above a predetermined defibrillation threshold for use in terminating heart fibrillation comprising:

a source of direct current;

and means, including a delay line discharge pulsing circuit having at least two inductance-capacitance sections and having a characteristic impedance of substantially 100 ohms, coupled to said direct current source and to said electrodes and actuatable to deliver through said electrodes, when applied to said body, only a single substantially trapezoidal pulse of direct current electrical energy for each actuation, said pulse being of at least 10 milliseconds duration and having a duty cycle in excess of 80%.

9. A universal electrical defibrillator for delivering electrical energy above a predetermined defibrillation threshold for use ineither transthoracic or exposed heart defibrillation comprising:

a pair of electrodes adapted to be applied internally or externally to the body of a living organism at spaced locations on opposite sides of the heart;

a source of direct current;

and means, consisting essentially of an actuator and fixed electrical circuit elements comprising a delay line discharge pulsing circuit having at least two inductance-capacitance sections and having a characteristic impedance of substantially 100 ohms, coupled to said direct current source and to said electrodes and actuatable to deliver through said electrodes when internally or externally applied to said body, only a single substantially trapezoidal pulse of electrical energy for each actuation, said pulse being of at least 10 milliseconds duration and having a predetermined duty cycle of at least 10. A universal electrical defibrillator for delivering electrical energy above a predetermined defibrillation threshold for use in either transthoracic or exposed-heart defibrillation comprising:

a source of direct current;

and means, consisting essentially of an actuator and fixed electrical circuit elements comprising an inductance-capacitance delay line having at least two inductance-capacitance sections and having a characteristic impedance of substantially ohms, coupled to said direct-current source and to said electrodes and actuatable to deliver through said electrodes when externally or internally applied to said body, only a single substantially trapezoidal pulse of electrical energy for each actuation, said pulse being of at least 10 milliseconds duration and having a predetermined peak amplitude less than 50% above said defibrillation threshold and a predetermined duty cycle of at least 80%.

11. In a portable electrical defibrillator having electrode means adapted to contact a patients body and a wholly self-contained battery power source, the combination comprising:

electronic means including a trasistorized inverter and a rectifier coupled to said battery for converting direct current from said battery to alternating current at a higher voltage and rectifying said alternating current to direct current at a higher voltage than that of said battery;

charge storage means coupled to said first-mentioned means and responsive to said higher-voltage direct current for accumulating a stored charge at a predetermined level required to deliver a defibrillating impulse on being discharged through the body of a living organism;

sensing means coupled to said charge storage means for developing a control effect proportional to the charge stored in said charge storage means;

and a :transistorized control circuit coupled to said sensing means and to said first-mentioned means and responsive to said control effect for actuating said firstmentioned means to maintain said stored charge at 13 circuit including said operating coil, said transistor switching device being provided with an operating bias, and in which said control effect is employed to vary said operating bias of said switching device.

14,' The combination according to claim 13, including additional means, responsive to operation of said switch device to disable said electronic means, for augmenting said operating bias applied to said transistor switching device in response to said control efiect.

References Cited by the Examiner UNITED STATES PATENTS RICHARD A. -GAUDET, Primary Examiner.

10 W. E. KAMM, Assistant Examiner.

Claims

1. A DIRECT-CURRENT MONOPULSE ELECTRICAL DEFIBRILLATOR COMPRISING: A DELAY LINE DISCHARGING PULSING CIRCUIT HAVING AT LEAST TWO INDUCTANCE-CAPACITANCE SECTIONS FOR PRODUCING ON DISCHARGE A SINGLE DIRECT-CURRENT OUTPUT PULSE HAVING A SUBSTANTIALLY TRAPEZOIDAL WAVESHAPE; MEANS FOR STORING A PREDETERMINED AMOUNT OF ENERGY IN SAID DELAY LINE DISCHARGE PULSING CIRCUIT; AND MEANS, INCLUDING A PAIR OF ELECTRODES COUPLED TO SAID DELAY LINE DISCHARGING PULSING CIRCUIT AND ADAPTED TO BE APPLIED TO THE BODY OF A LIVING ORGANISM AT SPACED LOCATIONS ON OPPOSITE SIDES OF THE HEART, ACTUATABLE SUBSEQUENT TO THE STORAGE OF SAID ENERGY