|Publication number||US3747605 A|
|Publication date||Jul 24, 1973|
|Filing date||Oct 20, 1971|
|Priority date||Oct 20, 1971|
|Publication number||US 3747605 A, US 3747605A, US-A-3747605, US3747605 A, US3747605A|
|Original Assignee||Beaumont Hospital William|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (5), Referenced by (56), Classifications (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent [1 1 Cook [451 July 24, 1973 DEFIBILLATOR AND METHOD AND APPARATUS FOR CALIBRATING, TESTING, MONITORING AND/OR CONTROLLING A DEFIBRILLATOR OR THE LIKE  Inventor: Kenneth J. Cook, Oak Park, Mich.
 Assignee: William Beaumont Hospital, Royal Oak, Mich.
 Filed: Oct. 20, 1971 ] Appl. No; 190,750
 (LS. Cl. 128/419 D, 128/421, 324/142  Int. Cl A61n 1/36 ['58] Field of Search 128/419 D, 419 R, 128/421, 423; 324/103, 140, 141, 142
 References Cited UNITED STATES PATENTS 2,900,605 8/1959 Squires et a1. 324/142 3,442,269 5/1969 Druz 128/419 D 3,517,311 6/1970 Wasielewski et all 324/142 FOREIGN PATENTS OR APPLICATIONS 969,659 9/1950 France 128/419 D 1,076,286 2/1960 Germany 128/419 D Primary ExaminerWilliam E. Kamm Attorney-Arthur Raisch, Chester L. Davis, Jr. et al,
 ABSTRACT An electronic energy analyzer circuit is connected to a defibrillator calibrating, testing, monitoring and controlling the energy output of the defibrillator used for treating certain cardiac conditions. Voltage and current of the defibrillator output are sensed and the resultant signals are multiplied to provide a power function which is thenintegrated to provide measurement of the total energy delivered. Energy measurements are performed separately on positive and negative half cycles of the defibrillator output. The time duration of the treatment and the peak voltage applied to the patient are also monitored. The defibrillator includes an auxiliary precision source to the calibrate meter scales in the analyzer. A dummy load is also provided to test the defibrillator output prior to treatment. During treatment, the energy actually delivered to the patient can be either controlled at a selected level or monitored.
25 Claims, 5 Drawing Figures -zr- 29 I to patient my I I /8 A /2 f,
a I defibrll- I 'm g t'il l l i I curren v- I ,9 swlich L. sensing we OUTPUT 0 circuits allied 9* /4 It a I I an analog 7 I fi CYCLE comparator I COMPLETE I I INDICATOR I J T I f I voltage ubsolute I digital I diff. value V threshold 1 control .65
amp. det. I f 4 5 58 I l f l 59 I I I peak umple y and I a I hold I V5 6 I I 42 5a cllfbl'm 30 J44 fI L I I. w "I i If I ntesampe qmp r multiplier I V dlff. I, V. 4 I p- I mod. I I I- I 49a 34b l "L. I
Pate rated July 24, 1973 2 Sheets-Sheet l aEu I'll-Ill IIIIIIIIIIIIII' KENNETH J. COOK BY Wk @4111?) ATTORN EYS DEFIBILLATOR AND METHOD AND APPARATUS FOR CALIBRATING, TESTING, MONITORING AND/OR CONTROLLING A DEFIBRILLATOR OR THE LIKE This invention relates to defibrillators and in particular to an energy analyzer for calibrating, testing, monitoring and controlling the energy output of a defibrillator or a cardioconverter. The defibrillator generates an output voltage which is applied via electrodes to the patient during treatment of certain cardiac conditions. For example, in treating cardiac conversion, a relatively low defibrillator voltage is applied across the chest cavity of a patient by paddle-type electrodes. The energy application is synchronized by an electrocardio gram (ECG) device connected to the patient. The ECG triggers operation of the defibrillator relative to certain bodily generated electrical impulses in the hope that the spurious premature beats characteristic of cardiac conversion will be suppressed. In treating cardiac fibrillation, the application of the defibrillator voltage to the fibrillating heart is intended to momentarily polarize the randomly contracting heart muscles in the hope that they will regain their normal synchronism. When fibrillation is treated surgically, electrode probes are placed directly in contact with the heart and the energy output of the defibrillator must be limited to prevent damage to the heart. When fibrillation is treated nonsu rgically, the defibrillator voltage is applied via paddle-type electrodes across the patients chest cavity and substantially greater energy is required to provide the necessary current distribution through the chest cavity so that sufficient current passes through the heart muscles to cause constriction thereof and terminate fibrillation.
Although defibrillators can often provide effective treatment for these and certain related types of cardiac malfunctions, there do not appear to be uniform procedures for treating patients or for specifying and calibrating the defibrillator output. This is undoubtedly due in part to variable factors such as the pressure and location of hand-held movable electrodes on a patient, the electrical resistance of the patient and the peak voltage and the energy delivered to the patient by the defibrillator. Also as was pointed out above, the energy levels for different types of treatment application differ. Although the defibrillator may be adjustably set to deliver a selected amount of energy, such an adjustment presupposes a known resistance through which the defibrillator output is to be delivered and further presupposes repeatability and accuracy of the defibrillator setting under varying conditions and after continued use. Hence in most situations, the actual energy delivered to the patient does not match and indeed may vary considerably, up to as much as 50 percent, from the intended energy set on the defibrillator by the operator. However, it is still desirable to periodically check the defibrillator output against the defibrillator setting by discharging through a dummy load, typically 50-60 ohms. On commercially available defibrillators, the
output is usually checked and calibrated in terms of totalenergy. There is also evidence that myocardial damage may be dependent on the peak voltage as well as duration of the applied energy. Certain malfunctions, for example, defective cables, may also go unnoticed.
The procedures are further complicated because the output voltage and current waveforms of commercial difibrillators, for example, a defibrillator of the delay line discharge type, may be generally characterized as damped oscillations. Hence the amplitude, frequency and duration of the applied energy and degree of damp ing will all be a function of the resistance of the patient and other variable parameters. The delay line parameters are selected so that most of the energy is delivered to the patient during the first half cycle of the applied voltage. However, often there is at least a second or opposite polarity half cycle of energy applied to the pa tient resulting in the alternating polarization of the heart muscles. Although the full significance of the opposite polarity energy is not fully understood, it has been found that knowledge of the magnitude of both half cycle energies and the magnitude of the associated peak voltage is valuable. Several techniques that have been used or at least proposed to measure output energy do not separately measure positive or negative half cycle energy and often they measure only net positive energy. Other more comprehensive techniques that have been proposed are either too time consuming or too expensive for practical commercial applications.
Even though treating personnel may. appreciate that the aforementioned variations occur, the significance and effect of these variations on the heart are not fully understood. Hence the operator will frequently set the defibrillator to a conservative energy level for the initialtreatment. If the first treatment is unsuccessful, the treatments will be repeated at successively higher energy levels. In any event, during the initial and subsequent treatments, the operator has little information about the energy actually applied to the patient due to variations between patients, differences between set and delivered energy, drift and inaccuracy in the defibrillator setting and the absence of sufficient monitors on commercial defibrillators. Thus a particular setup which has successfully treated one patient could possibly be injurious to another patient.
The primary objects of this invention are to provide an energy analyzer either alone or in combination with a defibrillator and method for a defibrillator that reduce the aforementioned uncertainties with prior art defibrillator techniques; that simplify defibrillator treatment procedures; that improve the reliability, accuracy and repeatability of defibrillator operation; that provide more useful information, at low cost, about the defibrillator output by comparison to the prior art; that effectively develop useful information about opposite polarity half cycle energy at the defibrillator output; and/or that accurately test, monitor and/or control the energy output of a defibrillator and the like.
Another object of this invention is to provide an energy analyzer and method which are compatible with various types of presently commercially available defibrillators and measure useful characteristics of the defibrillator output including separate measurements of opposite polarity half cycle energy.
A further object of this invention is to provide an energy controller and method for a defibrillator which permits treating personnel to accurately set an initial treatment level for an individual patient with confidence that the energy transferred tothe patient will not exceed the desired dosage;
A still further object of this invention is to provide an energy monitor for a defibrillator which accurately and rapidly provides useful information about a previously administered dosage to facilitate fast determination of the dosage for a subsequent treatment.
Other objects, features and advantages of the present invention will be apparent from the following description, the appended claims and the accompanying drawings in which:
FIG. 1 is a block diagram of the energy analyzer of the invention connected to a defibrillator;
FIG. 2 is a diagram, partly in block and partly in schematic, showing further details of a digital controller in the circuit of FIG. 1;
FIGS. 3a-3h show various waveforms useful in understanding the operation of the circuits of FIGS. 1 and FIG. 4 is a block diagram of a modification of FIG. 1 which includes a calibration source; and
FIGS. 5a-5c show various waveforms useful in understanding the operation of the diagram of FIG. 4.
Referring to FIG. 1, a defibrillator has its output connected via leads 12, 14, an electronic shunt switch 16, voltage and current sensing circuits 18 and leads l2, 14' to a pair of paddles 20, 22. A resistor 23 is arranged to be connected across leads 12, 14', in parallel with paddles 20, 22, via switch 25 as a dummy load for defibrillator 10. As will later be described in greater detail, the energy analyzer for defibrillator 10 can be operated in four different modes: 1) a meter calibration mode; 2) a test mode; 3) a monitoring mode; and 4) a control mode. Resistor 23 is connected via switch 25 to simulate the resistive load of a patient, typically 50-60 ohms, during calibration and test modes. During the monitoring and control modes, for nonsurgical treatment the energy is applied to the patient by placing paddles 20, 22 against the patients chest cavity. For surgical treatment, i;e., open heart, paddles 20, 22 are replaced with suitable probes for applying energy directly to the heart.
Defibrillator 10 is a commercially available unit, for example, of the delay-line discharge type, which includes a control knob 24 for setting the energy level of the defibrillator output and a switch 26 for actuating the defibrillator to discharge the delay line. Alterna" tively, defibrillator 10 may be actuated automatically by a stroke signal applied via switch 29 from an electrocardiogram (ECG) 27 which is operatively connected to the patient. Synchronized defibrillator operation is used in treating cardiac conversion. Switch 16 shortcircuits or crowbars the defibrillator output when the energy analyzer is operating in its control mode as will be described hereinafter. Sensing circuits 18 are of suitable construction to provide signals representing the output current I, and the output voltage V,. A high impedance voltage divider (not shown) may be connected across lines 12, 14 for sensing voltage and a calibrated current shunt (not shown) interposed in one of the lines 12, 14 for sensing current. In commercially available defibrillators, leads 12, 14 would be connected directly to paddles 20, 22 and some commercial models include a dummy load corresponding to resistor 23. Hence the energy analyzer of the present invention can be used with commercially available defibrillators by merely inserting switch 16 and circuits 18 between the defibrillator 10 and the paddles 20, 22. However, the present invention also contemplates an integrated unit wherein switch 16 and circuits 18 are incorporated in the defibrillator housing.
As previously indicated, the voltage waveform of a typical defibrillator is generally a damped sinusoidal oscillation as illustrated for the voltage V, in FIG. 3a. Although the voltage waveform V, is shown extending over several half cycles for purposes of explaining the present invention, in practice substantially all of the defibrillator energy may be transferred to a patient in the first few half cycles. Assuming a resistive load which is typically the case, the waveform for the current I, will be in phase with and correspond to the voltage waveform V,. In accordance with one aspect of the present invention, the odd numbered half cycles and the even numbered half cycles are analyzed separately for total energy. Peak voltage 31 and duration 33 are also measured. The voltage waveform V, and the remaining waveforms illustrated in FIG. 3 are intended primarily to show phase and timing relationships and hence are not necessarily to scale. For purposes of explanation, the first half cycle of V, is illustrated as positive but it will be understood that the present invention operates effectively regardless of the assumed polarity of the ini tial half cycle.
Referring again to FIG. 1, the voltage and current signals developed at circuits 18 are applied respectively to a voltage differential amplifier 28 and a current differential amplifier 30 which develop respective amplified versions, designated as V and V,, (FIG. 1), of the input signals. The signals applied to amplifier 28 and hence the signal V, represent the voltage V at the defibrillator output, either across resistor 23 during calibration and test modes or across the patient during monitor and control modes. Similarly, the signal applied to amplifier 30 and hence the signal V,, represent the current I through either resistor 23 or the patient depending on the mode of operation. Differential amplifiers (double ended input to single ended output) are used so that the amplifiers 28, 30 will respond to the signals from circuits 18 regardless of the polarity of the paddles 20, 22 or whether either one or both of the paddles are ungrounded. Hence the leads 12, 14 or the paddles 20, 22 can be reversed without affecting the circuit operation. The outputs of amplifiers 28, 30 are arranged to be connected to respective inputs of a multiplier module 32 via contacts 34a, 34b of a doublepole, double-throw switch 34. The output of amplifier 28 is also fed to an absolute value amplifier 36 whose output signal V (FIG. 3b) is arranged to be connected to both inputs of multiplier module 32 via contacts 34c, 34d of switch 34. Amplifier 36 performs full wave rectification on the signal V,,, from amplifier 28 so that the signal V, will always have the same polarity, that is, negative half cycles are automatically inverted whereas positive half cycles are unaltered. Hence the waveform of the signal V corresponds to the waveform of the voltage V, (FIG. 3a) with the negative half cycles inverted.
Module 32 multiplies the signal at one input by the signal at the other input to develop an output signal designated V,,. With the input to module 32 taken from contacts 34a, 34b, the output signal V,
represents the instantaneous power output (V, times l,), where V, is either the voltage across resistor 23 or across paddles 20, 22. Similarly, with the input to module 32 taken at contacts 34c, 34d, the output voltage V,, will be proportional to the instantaneous power, i.e., V divided by R where R is the resistance of resistor 23. The output signal V, from module 32 is fed to electronic switches 38, 40 which gate respective alternate half cycles to integrators 42, 44 in response to switching signals V V (FIGS. 3e, 3f) sullied from a digital control 46 on lines 39, 41, respectively. Hence odd numbered half cycles (positive half cycles as referenced to the polarity of the waveforms of FIG. 3) are integrated at 42; and even numbered half cycles (negative half cycles as referenced to the polarity of the waveforms of FIG. 3) are integrated at 44.
As will later be described in greater detail, digital control 46 develops timing signals, including the switching signals V V in response to .an input signal V (FIG. 3a developed by a threshold detector 48 from the output signal V of amplifier 36. The signal V consists of a series of constant amplitude pulses 47, with the duration of each pulse corresponding to the duration that its corresponding half cycle in the voltage V, is above a predetermined threshold level 49 (FIG. 3b). Although the level 49 and the spacing between pulses 47 are exaggerated in FIG. 3b for purposes of illustration, in practice the threshold 49 may be very close to zero and hence the duration of the pulses 47 in the signal V is substantially equal to that of its associated half cycle in the signal V Hence the leading edge of each pulse 47 in the signal V is synchronized substantially with the zero crossing in the original output voltage in V As exaggerated in FIG. 30, the decreasing peak amplitude of successive half cycles of the signal V will cause a slight reduction in the width of successive pulses in the signal V The train of pulses 47 from detector 48 terminates when the peak half cycle amplitude drops below the threshold level 49. The output of amplifier 36 is also fed to a peak detector 54 which detects and holds the peak value of the highest amplitude half cycle in the voltage V corresponding to the peak value 31 of voltage V,. The pulse train 47 from detector 48 is also fed to an integrator 56 for measuring the duration 33 of the defibrillator output. Since the pulses 47 are of constant amplitude and the spacing between the pulses negligible, although exaggerated in FIG. 3, the ramp developed at integrator 56 will have a final value corresponding to the duration 33 ending when the voltage V drops below level 49.
Integrators 42, 44 continue to integrate the respective odd and even half cycles until the defibrillator output has decayed to a point where the output V of the amplifier 36 drops below the threshold level 49. Hence the outputs V V (FIGS. 3g, 3h, respectively) represent the total energy in the odd and even half cycles, respectively. When the output V drops below the threshold level 49, the integrated outputs at integrators 42,44 are transferred to respective sample-and-hold circuits 50, 52 in response to a strobe signal provided on lead 53 from the digital control 46. Simultaneously, the strobe signal on line 53 transfers the peak voltage from detector 54 to a sample-and-hold circuit 58 and the duration signal at integrator 56 to a sample-andhold circuit 60. Immediately after sampling, integrators 42, 44, 56 and peak detector 54 are reset by a reset pulse on line 55 from the digital control 46. The respective outputs of the four sample-and-hold circuits 50, 52, 58, 60 are connected via a four-position selector switch 62 through an amplifier 64to a meter 66. Meter 66 is provided with calibrated scales so that the peak voltage, duration and positive and negative energy can be read directly. One scale on meter 66 can be calibrated directly in units of energy for the case where the inputs at module 32 are taken at contacts 34a, 34b. For the case where the inputs to module 32 are taken at contacts 34c, 34d, a separate meter scale is calibrated based on the value of resistor 23, for example, 50 ohms, so that the energy can be read directly based on a computation of V divided by R.
It is also noted that the integrated signals V V from the respective integrators 42, 44 are fed to a summing amplifier and analog comparator 106. Comparator 106 also has an adjustable reference input at potentiometer 108. When the sum of the signals V and V reaches the level set on potentiometer 108, comparator 106 generates an output level which is arranged to be coupled through a switch 109 to the electronic shunt switch 16. Switch 16 may be of suitable construction, such as a triac, to short circuit the defibrillator output on opposite polarity half cycles. When operating in the calibration mode, a maximum total energy level is set on potentiometer 108 and as soon as the sum of the energy levels represented by voltages V and V exceed the reference energy level, electronic switch 16 is energized to short-circuit the remainder of the defibrillator output.
Referring to the circuit for digital control 46 as shown in FIG. 2, the pulses 47 from detector 48 are fed to a system reset flip-flop 68 and to a half-cycle reset circuit 74. Flip-flop 68 also has a reset input that is energized via a reset push button70. Push button 70 is closed momentarily before operating defibrillator 10 to light a reset indicator 72 and ready control 46 for the signal V Upon operation of defibrillator 10, the lead ing edge of the first rectangular pulse of waveform V3 sets flip-flop 68 and triggers a half cycle reset circuit 74. Setting of flip-flop 68 turns. indicator 72 off and starts a timer 76 which is repetitively reset by subsequent voltage spikes V (FIG. 3d) generated by circuit 74 in response to the leading edges of the pulses 47. The time required for timer 76 to time out after being reset by each spike in the signal V is slightly greater than the time duration of the longest expected half cycle of signal V So long as the peak half cycle voltage in signal V exceeds the threshold 49, timer 76 will not time out. When the peak level of signal V drops below the threshold level 49, timer 76 will time out to energize a strobe initiate circuit 84 and a delay circuit 86.
The strobe initiate circuit 84 provides the strobe signal on line 53 to gate the sample-and-hold circuits 50, 52, 58, 60. The sample-and-hold circuits 50, 52, 58, 60 may be of suitable construction such as a capacitor connected to its associated integrator 42, 44, 46 and peak detector 54 via an electronic switching device such as a metal oxide semi-conductor field effect transistor (MOSFET). MOSFETS have a very high input impedance in the absence of a strobe signal on line 52 to effectively isolate the sample-and-hold circuits from the signal to be sampled. When the MOSFET is gated on by the strobe signal on line 53, the input impedance to the capacitor is very low so that the capacitor charges almost instantaneously to the level of the input signal. At the end of thestrobe signal, the MOSFET turns off to again isolate the sample-and-hold circuits 50, 52, 58,60 fromtheir respective inputs to hold the sample onthe'capacitor for readingvia switch 62 and meter 66. Conventionally, the capacitors in the sample the meter 66 does not load the sample-and-hold circuits. In response to the .output from timer 76, a slightly delayed reset pulse is provided on line 55 via the delay circuit 86 to reset integrators 42, 44, 56 and peak detector 54. The reset pulse from delay circuit 86 also lights a cycle complete indicator 88. The slight delay is introduced by circuit 86 to assure that sample-and-hold circuits 50, 52, 58, 60 have sufficient time to sample their respective inputs.
The pulses 47 from detector 48 are also applied to a classifying flip-flop 78 and first inputs of respective AND gates 80, 82. The reset output of flip-flop 78 is connected to the other input of AND gate 80 and the set output of flip-flop 78 to the other input of AND gate 82. Flip-flop 78 is responsive to the leading edges of pulses 47 to alternately enable gates 80, 82 and thereby steer the pulses 47 alternately to amplifier circuits 83, 85. Amplifiers 83, 85 in turn provide the switching signals V V on lines 39, 41 to alternately operate switches 38, 40. Switches 38, 40 are preferably MOS- FETS having fast switching characteristics. Switch 38 operates whenever a pulse is supplied from amplifier 85 and switch 40 whenever a pulse is supplied from amplifier 83. The pulse outputs of amplifiers 85, 83 are illustrated in FIGS. 3e and 3f, respectively, as V and V The pulses of waveform V are coextensive with the odd numbered half cycles of waveform V and the pulses of waveform V with the even numbered half cycles. With this arrangement, switch 38 operates during substantially the entire duration of each positive half cycle of voltage V to couple the signal V to integrator 42 during odd (positive) half cycles of V and to integrator 44 during even (negative) half cycles. As can be seen by comparison of FIGS. 3g and 3h to FIG. 3a, at any given time the integrated voltages V-, and V at integrators 42, 44, respectively, are a measure of the energy transferred to the defibrillator load, either resistor 23 or the patient (via paddles 20, 22), during the respective odd (positive) half cycles and even (negative) half cycles of V The magnitudes of signals V and V increase in increments of decreasing size until the amplitude of voltage V becomes so low that the amplitude of voltage V fails to rise above the threshold level 49 and timer 76 times out.
When flip-flop 68 is reset by push button 70, flip-flop 78 is also reset via the set output of flip-flop 68 to assure that the first pulse 47 in the signal V is steered through gate 80 to amplifier 85. Therefore, gate 80 is always the first gate through which a pulse 47 is transmitted and this guarantees that integrator 42 will always integrate the odd numbered half cycles of voltage V and integrator 44 the even numbered half cycles. Because amplifier 36 produces only a positive output independent ofthe polarity of its input, the connection of paddles 20, 22 to the defibrillator may be reversed without affecting the operation of the energy analyzer. Similarly, because peak detector 54 is responsive to the peak value of the rectified signal V the peak magnitude of voltage V is detected independent ofits polarity.
Before summarizing the overall operation, attention is directed to FIG. 4 which illustrates a simplified version of the circuit of FIG. 1. FIG. 4 also includes meter calibration that can be used with the circuit of FIG. 1. The circuit of FIG. 4 replaces only that portion of the corresponding circuit enclosed in dashed lines in FIG. I, and the remainder of the circuit for FIG. 4 may be the same as that outside the dashed lines in FIG. 1 except that switch 16 and comparator 106 have been omitted to simplify the disclosure. Since certain components in FIG. 4 are substantially the same as corresponding components in FIG. 1, like reference numbers will be used to indicate like components. Defibrillator 10 has its output connected via leads 12, 14, switch 112, leads 12', 14' to paddles 20, 22. A precision pulse train from a calibration pulse generator 114 is arranged to be connected across lines 12, 14' when switch 112 is in its dashed position. A voltage divider 116 is connected across leads 12, 14 to sense the voltage thereacross; i.e., either the output from defibrillator 10 or from pulse generator 114. The voltage signal from divider 116 is fed to differential amplifier 28 whose output V is connected to absolute value amplifier 36. As in the circuit of FIG. 1, amplifier 36 feeds the rectified signal V (FIG. 3b) to detector 48, multiplier module 32 and a peak detector 54 (FIG. 1). Similarly as in FIG. 1, detector 48 develops the pulse train V (FIG. 3e) which is fed to a digital control 46 and an integrator 56 (FIG. 1). Module 32 squares the signal V to develop the signal V which is fed to electronic switches 38, 40 (FIG. 1).
By comparison of FIGS. 1 and 4, the substitution of the circuit of FIG. 4 in place of the corresponding circuit in FIG. 1 enclosed within dashed lines will be apparent. Hence voltage divider 116 corresponds to the voltage sensing portion of circuit 18 (FIG. 1). When switch 112 is in the position shown in full lines in FIG. 4, the operation of FIG. 4 will be substantially the same as that described in connection with FIG. 1 for the case where the module input 32 (FIG. 1) is taken at the contacts 34c, 34d. To calibrate meter 66 (FIG. 1), switch 112 is moved to its dashed position and resistor 23 is connected across lines 12', 14' by closing switch 25. Generator 114 can be selectively set to provide one of the three pulse trains illustrated as P,, P P in FIGS. 5a, 5b, 5c, respectively. All of the pulses in the pulse train P, for example, are identical and are accurate square waves whose amplitude and width are accurately set at the factory. Hence during calibration, the energy in the odd numbered pulses of the pulse train P will be developed at integrator 42 and the energy in the even numbered pulses at integrator 44 in the manner described in connection with FIG. 1. Since the energy in the odd numbered and even numbered pulses is known, meter 66 can be accurately calibrated for odd and even half cycle energy. To this end, the reading on meter 66 in response to the pulse train P can be calibrated by suitably adjusting the gain of the circuit, for example, at the voltage divider 116 or at amplifier 64.
The pulse train F can also be used to separately calibrate meter 66 for peak voltage and time duration in addition to odd and even half cycle energy. For separate calibration of each meter scale, the gain would be adjusted in each channel, for example, by suitable amplifiers in each of the respective outputs of thesampleand-hold circuits 50, 52, 58, 60. Since the energy in the pulse train from generator 114 and hencethe output of integrators 42, 44 will be directly proportional to the number of pulses, meter 66 can be calibrated at different energy levels by merely applying different numbers of pulses to integrators 42, 44. By providing twice the number of pulses in pulse train P,, as compared to pulse train P meter 66 can be calibrated at twice the energy level, and similarly at three times the energy level with pulse train P Although calibration by using the pulse generator 114 has been described in connection with the simplified circuit version of FIG. 4, it will be understood that the identical calibration feature can be incorporated into FIG. 1 by insertion of a switch corre sponding to switch 112 in lines l2, 14 at the input of circuits 18. FIG. 4 also illustrates that effective energy measurements can be obtained using a simple squaring circuit for module 32 although the measurement based on V, times I, in the circuit of FIG. 1 is preferred, particularly for measuring energy actually delivered to the patient.
Referring back to the overall operation of the circuit shown in FIG. 1, assuming that meter 66has been accurately calibrated as by the calibration technique described in connection with FIG. 4, the output of defibrillator 10 may be tested for selected energy settings of knob 24. During the testing mode, dummy load resistor 23is again connected across leads 12, 14 by closing switch 25. For example, as indicated earlier, commercially availabledefibrillators typically have a total energy setting on' knob 24. Hence the operator can set a desired total energy level on defibrillator l and then, during the test mode, determine the peak voltage and time duration as well as the odd and even half cycle energy for that setting. Additionally, where knob 24 sets only the total energy, the setting can be checked by adding the readings obtained on-meter 66 for both the odd and even half cycle energy readings. The operator can then readjust the setting at knob 24 to obtain any givenoddor even half cycle energy level or total energy level as required to prevent excessive energy applications to a patient. Test mode operation is desirable because the actual output of commercially available defibrillators quite frequently does not correspond to the defibrillator setting. Additionally, commercially available defibrillators do not have the capability to selectively set the energy in the positive and negative half cycles of the damped output. During thetest mode, the switch 34 can be set to either the position illustrated in full lines or the position illustrated in broken lines in FIG. 1. In the full line position of switch 34, the odd and even half cycle energy will be determined based on the computation of the square of the voltage V, divided by the resistance R of resistor 23. In the dashed line position of switch 34, the odd andeven half cycle energy will be determined based on the computation of multiplying the voltage V, across resistor 23 by the current I, through resistor 23. In either position of switch 34, the energy levels read at meter 66 should be the same.
During the monitoring mode, switch 25 is open so that when defibrillator is operated the energy analyzer responds to the voltage and current applied directly to the patient via paddles 20, 22. Preferably, monitoring is performed with switch 34 in the position illustrated in dashed lines so that the energy computation is based on V, times I,. At the end of a treatment,the operator can obtain useful information for subsequent treatmentby sequencing switch 62 to read the values of peak voltage and time duration and positive and neg ative half cycle energy. As indicated earlier, the present invention also contemplates four separate meters'to continuously monitor the information in the sampleand-hole circuits 50, 52, 58, 60.
When operating in the control mode, potentiometer 108 is set to a position correspondingto the maximum energy to be applied to the patient. The operator then actuates switch 109 to connect comparator 106 to switch 116. Operation in the control mode can be performed simultaneously with the monitoring mode or separately therefrom. In either case, when the level at one of the integrators 42, 44 reaches the level set at potentiometer 108, switch 16 is energized to short the defibrillator output and prevent the further application of energy to the patient. Of course, the energy applied to the patient while operating in the control mode can be checked on meter 66 since the signal corresponding to signal V, will immediately drop below a threshold level 49 when switch 16 is operated.
The energy analyzers described] hereinabove can provide effective calibration, testing, monitoring and con trol of the defibrillator output over a wide range of energy levels. For example, to treat a fibrillating heart nonsurgically with paddles 20, 22 placed on the patients chest, the total applied energy is typically in the range of from 100400 watt-seconds. Surgical treatment of a fibrillating heart may require energy in the range of 20-50 watt-seconds. Nonsurgical treatment of cardiac conversion'requires the synchronized application of energy in the range of 5-100 watt-seconds. For defibrillator operation in these ranges, an operator using the analyzer of the present invention obtains substantial useful information about the output waveform, both prior to and during treatment. The operator knows, qualitatively, whether negative half-cycle energy is applied tothe. patient. With experienceand further development of treatment procedures, the quantitative significance of the negative half-cycle energy will become more valuable. This information can reduce the uncertainties presently associated with defibrillator treatment, increase the efficiency, speed and effectiveness of defibrillator treatment and reduce the risk of excessive energy application and burning and scarring of the patient. The energy analyzers described are simple to operate and direct reading. Where the energy analyzer is a separate unit from the defibrillator unit, the analyzer unit is easily'portable so that defibrillators can be tested without removing them from the area where they are needed. Although particular circuits have been disclosed, other modifications are also contemplated by the present invention. For example, the power measurement based on'V, times I, (FIG. 1) or Vf/R (FIGS. 1 and 4) could also be based on I, R by simply squaring the current signal at amplifier 30 (FIG. 11). However, power measurement based on V, times I, is preferred. Similarly, with suitable circuit modification, switches 38, 40 could be gated in accordance with the transition between adjacent half cycles sensed directly from the power voltage V,,, although switching according to the voltage V, is preferred.
It will be understood that the energy analyzer for defibrillators and the corresponding method have been described hereinabove for purposes of illustration and are not intended to limit the present invention, the scope of which is defined by the following claims.
I. An energy analyzer circuit for use with a defibrillator or the like of the type having output terminals and electrodes coupled to said terminals and adapted to contact a patient during treatment of a cardiac condition, said defibrillator providing voltage and current outputs having generally damped oscillatory waveforms when said defibrillator is connected to a load that is either said patient or a dummy load simulating said patient, each of said outputs having at least a first excursion at a first polarity and a second excursion at a second polarity opposite said first polarity, said analyzer circuit comprising sensing means adapted to be coupled to said output terminals and responsive to at least a first of said outputs to provide first electrical signals that represent said first output, power measuring means coupled to said sensing means and responsive to said first electrical signals to provide second electrical signals representing power transferred to said load when one of said outputs is at one polarity and third electrical signals representing power transferred to said load when said one output is at an opposite polarity, first integrator means coupled to said power measuring means and responsive to said second electrical signals to generate fourth electrical signals representing energy transferred to said load when said one output is at its said one polarity, second integrator means coupled to said power measuring means and responsive to said third electrical signals to provide fifth electrical signals representing energy transferred to said load when said one output is at its said opposite polarity, and indicator means coupled to said first and said second integrator means and responsive to said fourth and fifth electrical signals to provide first and second indications of energy transferred to said load when said one output is at its said one polarity and its said opposite polarity respectively.
2. The analyzer circuit set forth in claim 1 wherein said dummy load comprises an impedance and said analyzer circuit further comprises switch means for selectively connecting said impedance across said output terminals.
3.The analyzer circuit set forth in claim 1 wherein said first output is said voltage output and said first electrical signals represent said voltage across said load, and wherein said measuring means comprises means for squaring said first signals whereby said second and said third signals are proportional to power transferred to said load.
4. The analyzer circuit set forth in claim 3 wherein said power measuring means includes first and second electrical switching means connected to an output of said squaring means and responsive to switching signals to provide said second and said third electrical signals, and means for generating said switching signals in accordance with said one output.
5. The analyzer circuit set forth in claim 4 wherein said one output is said voltage output and wherein said switching signal generator means is coupled to said sensing means to generate said switching signals in accordance with said voltage output and said first and second switch means are responsive to said switching signals to actuate alternately on corresponding alternate excursions in said voltage output.
6. The analyzer circuit set forth in claim 5 further comprising peak detector means coupled to said sensing means and responsive to said first signal to provide a sixth electrical signal representing a peak level of that one of said first and second voltage excursions which has an amplitude greater than the other voltage excursion, and wherein said indicator means is responsive to said sixth electrical signal to provide an indication of said peak level.
7. The analyzer circuit set forth in claim 5 further comprising detector means responsive to said first electrical signals for generating a sixth electrical signal so long as said voltage output is above a predetermined level, duration measuring means coupled to said detector means and responsive to said sixth electrical signal to generate a seventh electrical signal representing the duration of said voltage output and wherein said indicator means is responsive to said seventh electrical signal to provide an indication of said voltage duration.
8. The analyzer circuit set forth in claim 5 further comprising detector means responsive to said first electrical signals for generating a sixth electrical signal when said voltage output drops below a predetermined level, first sample-and-hold means coupled between said first integrator means and said indicator means to store said fourth electrical signal in response to said sixth electrical signal, and second sample-and-hold means coupled between said second integrator means and said indicator 'means to store said fifth electrical signal in response to said sixth electrical signal.
9. The analyzer circuit set forth in claim 3 further comprising a pair of input terminals adapted to be connected to respective defibrillator output terminals and wherein sensing means comprises differential amplifier means to generate said first electrical signals independent of the polarity of the connection between said input terminals and said output terminals.
10. The analyzer circuit set forth in claim 1 wherein said sensing means is responsive to said voltage output and said current output to generate a first component signal representing output voltage variations and a second component signal representing output current variations and wherein said power measuring means comprises means for multiplying said first component signal times said second component signal whereby said second and third electrical signals represent power transferred to said load.
1 l. The analyzer circuit set forth in claim 10 wherein said power measuring means includes first and second electrical switching means connected to an output of said multiplying means and responsive to switching signals to provide said second and said third electrical signals, and means for generating said switching signals in accordance with said one output.
12. The analyzer circuit set forth in claim 10 wherein said one output is said voltage output and wherein said switching signal generator means is coupled to said sensing means and is responsive to said first component signal to generate said switching signals in accordance with said voltage output and wherein said first and said second switch means are responsive to said switching signals to actuate alternately on corresponding alternate excursions in said voltage output.
13. The analyzer circuit set forth in claim 12 further comprising peak detector means coupled to said sensing means and responsive to said first component signal to provide a sixth electrical signal representing a peak level of that one of said first and second voltage excursions which has an amplitude greater than the other 7 voltage excursion, and wherein said indicator means is duration of said voltage output and wherein said indica tor means is responsive to said seventh electrical signal to provide an indication of said voltage duration.
15. The analyzer circuit set forth in claim 12 further comprising detector means responsive to said first component signal to generate a sixth electrical signal when said voltage output drops below a predetermined level, first sample-and-hold means coupled between said first integrator means and said indicator means to store said fourth electrical signal in response to said sixth electrical signal, and second sample-and-hold means coupled between said second integrator means and said indica tor means to store said fifth electrical signal in response to said sixth electrical signal.
16. The analyzer circuit set forth in claim further comprising a pair of input terminals adapted to be connected to respective defibrillator output terminals, and wherein said sensing means comprises first differential amplifier means to generate said first component signal independent of the polarity of the connection between said input terminals and said output terminals, and second differential amplifier means to generate said second component signal independent of the polarity of theconnection between said input terminals and said output terminals.
17. The analyzer circuit set forth in claim '1 further comprising reference means for setting a predeterminedmaximum level of energy to be transferred to said patient, comparator means for comparing said predetermined energy level with at least one of said fourth and fifth signals and generating a comparison signal when. energy transferred to said patient exceeds said predetermined energy level, and means responsiveto said comparison signal for terminating further energy transfer from said defibrillator output to said patient.
18. The analyzer circuit set forth in claim 1 wherein said power measuring means comprises multiplication circuit means responsive to said first electrical signals .to provide an intermediate signal proportional to power transferred to said load, means for generating first and second switching signals insynchronism with said first and second excursions, respectively, of said one output, first electronic switch means coupled between said multiplication circuit means andsaid first integrator means and responsive to said first switching signal to connect said intermediate signal to said first integrator means during said first excursion of said one output and second electronic switch means coupled between said multiplication means and said second integrator means and responsive to said second switching signal to connect said intermediate signal to said second integrator means during said second excursion of said one output.
19. The analyzer circuit set forth in claim 18 further comprising a pair of input terminals adapted to be connected to said defibrillator output terminals, and wherein said sensing means comprises differential amplifier means to generate said first electrical signals independent of the polarity of the connection between saidinput terminals and said defibrillator output terminals, and wherein said switching signal generating means comprises means coupled to said differential amplifier means to rectify said first electrical signals and provide a pulse train of predetermined polarity in dependent of the polarity of the connection between said input terminals and said output terminals.
20. The analyzer circuit set forth in claim 1 further comprising a pair of input terminals adapted to be connected to said defibrillator output terminals and wherein said sensing means comprises differential amplifier means to generate said first electrical signals independent of the polarity of the connection between said input terminals and said defibrillator output terminals.
21. The analyzer circuit set forth in claim 1 wherein said indicator means comprises .a first visual display means responsive to said fourth electrical signal to provide a first visual indication of energy transferred to said load when said one output is at its said one polarity and second visual display means responsive to said fifth electrical signal to provide a second visual indication of energy transferred to said load when said one output is at its said opposite polarity.
22. In combination with a defibrillator or the like having a pair of output terminals and electrodes coupled to said terminals and adapted to contact a patient during treatment of a cardiac condition, means for terminating transfer of electrical energy to a patient during treatment when energy delivered to said patient reaches a predetermined level comprising first circuit means coupled to said output terminals to sense an electrical output at said terminals and provide a first electrical signal representing said electrical output, second circuit means responsive to said first electrical signal to provide a second electrical signal representing electrical energy transferred to said patient, adjustable reference means for setting said predetermined level of energy to be transferred to said patient, comparator means for comparing said predetermined energy level with said second signal and generating a comparison signal when energy transferred to said patient reaches said predetermined energy level and means responsive .to said comparison signal for interrupting further energy transfer from said defibrillator output terminals to said electrodes.
23. The combination. set forth in claim 22 wherein said transfer interruption means comprises electronic switch means coupled across said output terminals for substantially short-circuiting said output terminals in response to said comparison signal.
24. The combination set forth in claim 22 wherein said second circuit means comprises means responsive to said first electrical signal to develop a power signal comprising a series of electrical pulsations, first energy circuit means responsive to odd numbered pulsations in said power signal to develop a first energy component signal representing energy transferred to said patient during odd numbered pulsations of said power signal and second energy circuit means responsive to even numbered pulsations in said power signal to develop a second energy component signal representingenergy transferred to said patient during even numbered pulsations of said power signal, and wherein said comparator means further comprises means for summing saidfirst and said second component signals to provide said second electrical signal for comparison against said predetermined energy level. l l
25. The method of monitoring electrical energy transferred from output terminals of a defibrillator or the like to electrodes in contact with a patient during treatment of a cardiaccondition comprising connecting across said output terminals a load that is either said patient or a dummy load simulating said patient, generating at said output terminals voltage and current outputs having generally damped oscillatory waveforms and measuring energy transferred to said load during even numbered pulsations in said series of power pulsations to thereby obtain separate indications of energy transferred to said patient during odd and even energy measuring energy transferred to said load during odd pulsations.
numbered pulsations in said series of power pulsations 2223 UNITED STATES PATEN OFFICE v CERTIFICATE OF CORRECTION Patent No. ,747, 05 Dated July 24, 1973 inventor J C It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
F- On the information cover page, Column 1, line 1 of the title, Defibillator" should be --Defibrillator- Column 2, line 2 of the -Abstract", after "defibrillator" insert "for".
Column 1, line 1 ofthe title, "Defibillator" should be Column 2, line 20, or" should be "and".
Column 5, line 3, "sullied" should be -supplied--. lines 18 and 19, "calibration" should be "control-f. Column 11, claim 6, line 58, "signal" should be --signals--.
Column 12, claim 14, line 61, "13" should be --l2--.
Signed and sealed this 1st day of January 197C.
EDWARD M.FLETCHER,JR. RENE D. TEGTMEYER Attesting Officer Acting Commissioner ofTPatents
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US2442269 *||Feb 11, 1947||May 25, 1948||Frank Gromer Richard||Manifold check duplicating device|
|US2900605 *||May 20, 1955||Aug 18, 1959||Westinghouse Electric Corp||Electrical measuring system|
|US3517311 *||Dec 26, 1968||Jun 23, 1970||Pranor Ind Inc||Pulse accumulating watt-hour measuring system|
|*||DE1076286A||Title not available|
|FR969659A *||Title not available|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US3860009 *||Mar 13, 1974||Jan 14, 1975||Bell David||Computer controlled defibrillator|
|US3862636 *||Nov 29, 1973||Jan 28, 1975||Health Technology Labs Inc||Computer controlled defibrillator|
|US3869661 *||Jun 21, 1973||Mar 4, 1975||Centre Etd Ind Pharma||Stimulating device having a controlled power|
|US3886950 *||Oct 1, 1973||Jun 3, 1975||Spacelabs Inc||Defibrillator|
|US3952750 *||Apr 25, 1974||Apr 27, 1976||Mieczyslaw Mirowski||Command atrial cardioverting device|
|US3961173 *||Nov 20, 1974||Jun 1, 1976||Varian Associates||Heat unit integrator for X-ray tubes|
|US3983476 *||Jun 28, 1974||Sep 28, 1976||Francis Konopasek||Defibrillator testing device|
|US4167189 *||Mar 28, 1977||Sep 11, 1979||Agency Of Industrial Science & Technology||Apparatus for transmission of information by electrocutaneous stimulus|
|US4316472 *||Aug 9, 1979||Feb 23, 1982||Mieczyslaw Mirowski||Cardioverting device with stored energy selecting means and discharge initiating means, and related method|
|US4372324 *||Aug 17, 1981||Feb 8, 1983||Hewlett-Packard Company||Analog peak voltage detector in a defibrillator|
|US4566457 *||Jul 24, 1985||Jan 28, 1986||Gunter Stemple||Defibrillator circuit and electrodes therefor|
|US4572191 *||Feb 23, 1984||Feb 25, 1986||Mieczyslaw Mirowski||Command atrial cardioverter|
|US4574810 *||Oct 5, 1984||Mar 11, 1986||Lerman Bruce B||Automatic threshold defibrillator|
|US4628935 *||Jan 8, 1985||Dec 16, 1986||Physio-Control Corporation||Defibrillator adapted for use with accessory cassettes|
|US4693253 *||Mar 23, 1981||Sep 15, 1987||Medtronic, Inc.||Automatic implantable defibrillator and pacer|
|US4716897 *||Jul 3, 1986||Jan 5, 1988||Olympus Optical Co., Ltd.||Electrosurgical apparatus|
|US4823796 *||Apr 3, 1987||Apr 25, 1989||Laerdal Manufacturing Corp.||Defibrillator circuit for producing a trapezoidal defibrillation pulse|
|US4862889 *||Jan 19, 1989||Sep 5, 1989||Siemens Aktiengesellschaft||Monitoring circuit for an RF surgical apparatus|
|US5115807 *||Jan 7, 1991||May 26, 1992||Ventritex||Programmable defibrillator with pulse energy and resistance displays and methods of operating the same|
|US5137021 *||Nov 29, 1990||Aug 11, 1992||Medtronic, Inc.||Lead current measurement circuit|
|US5225769 *||Feb 21, 1992||Jul 6, 1993||Zmd Corporation||Defibrillation discharge current sensor|
|US5295481 *||Nov 1, 1991||Mar 22, 1994||Geeham Calvin T||Cardiopulmonary resuscitation assist device|
|US5366484 *||Apr 9, 1992||Nov 22, 1994||Angeion Corporation||Short-pulse cardioversion system for an implantable cardioverter defibrillator|
|US5611815 *||Dec 8, 1994||Mar 18, 1997||Heartstream, Inc.||Defibrillator with training features|
|US5620469 *||Oct 11, 1994||Apr 15, 1997||Angeion Corporation||Stepped cardioversion system for an implantable cardioverter defibrillator|
|US5662690 *||Jun 28, 1996||Sep 2, 1997||Heartstream, Inc.||Defibrillator with training features and pause actuator|
|US5662696 *||Sep 28, 1995||Sep 2, 1997||Angeion Corp||One piece disposable threshold test can electrode for use with an implantable cardioverter defibrillator system|
|US5720767 *||Oct 2, 1996||Feb 24, 1998||Pacesetter, Inc.||Impedance dependent implantable cardioverter-defibrillator|
|US5730766 *||Nov 5, 1996||Mar 24, 1998||Bha Group, Inc.||Non-round unitary filter cartridge|
|US5746792 *||Oct 25, 1996||May 5, 1998||Bha Group Holdings, Inc.||Dust collector filter element and supporting structure|
|US5800460 *||Apr 16, 1997||Sep 1, 1998||Heartstream, Inc.||Method for performing self-test in a defibrillator|
|US5879374 *||May 10, 1994||Mar 9, 1999||Heartstream, Inc.||External defibrillator with automatic self-testing prior to use|
|US5899925 *||Aug 7, 1997||May 4, 1999||Heartstream, Inc.||Method and apparatus for aperiodic self-testing of a defibrillator|
|US6016059 *||Jun 6, 1995||Jan 18, 2000||Heartstream, Inc.||Defibrillator system condition indicator|
|US6031369 *||Mar 8, 1996||Feb 29, 2000||Horstmann Timers & Controls Limited||Electricity meter having circuitry for selecting the conditioning of a power signal according to the polarity of an A.C. mains signal|
|US6075369 *||Jul 10, 1996||Jun 13, 2000||Heartstream||Defibrillator system condition indicator with an electrode interface|
|US6208898||Mar 25, 1999||Mar 27, 2001||Agilent Technologies, Inc.||Impedance estimation with dynamic waveform control in an electrotherapy apparatus|
|US6299574 *||Oct 13, 2000||Oct 9, 2001||Agilent Technologies, Inc.||Electrotherapy apparatus|
|US6317635||Jun 30, 1999||Nov 13, 2001||Dennis E. Ochs||Sensor responsive electrotherapy apparatus|
|US6400984||Jun 9, 2000||Jun 4, 2002||Medtronic Physio-Control Manufacturing Corp.||Method and apparatus for detecting whether a load is a patient or a test device|
|US7725180 *||Nov 29, 2004||May 25, 2010||Physio-Control, Inc.||Method and apparatus for testing an alternating current power source for defibrillation compatibility|
|US8090437||Apr 8, 2010||Jan 3, 2012||Physio Control, Inc.||Method and apparatus for testing an alternating current power source for defibrillation compatibility|
|US8417327||Jun 20, 2002||Apr 9, 2013||Physio-Control, Inc.||Variable frequency impedance measurement|
|US8696035||Oct 27, 2010||Apr 15, 2014||Bha Altair, Llc||Venturi adapter|
|US20030236468 *||Jun 20, 2002||Dec 25, 2003||Chapman Fred W.||Variable frequency impedance measurement|
|US20060116726 *||Nov 29, 2004||Jun 1, 2006||Sullivan Joseph L||Method and apparatus for testing an alternating current power source for defibrillation compatibility|
|US20060258193 *||May 12, 2005||Nov 16, 2006||Cardiac Pacemakers, Inc.||Lead terminal multi-tool|
|US20100194425 *||Aug 5, 2010||Physio-Control, Inc.|
|DE2701234A1 *||Jan 13, 1977||Jul 20, 1978||Inform Elektromedizinische Ger||Heart beat regulating pulse generator - determines pulse charge quantity by integrating current flow between electrodes|
|DE3222315A1 *||Jun 14, 1982||Dec 30, 1982||Medtronic Inc||Vorrichtung und verfahren zum bestimmen des energieinhalts eines elektrischen koerperreizimpulses|
|EP0699092A1 *||May 18, 1994||Mar 6, 1996||Heartstream, Inc.||Defibrillator with self-test features|
|EP1683544A1 *||May 18, 1994||Jul 26, 2006||Philips Electronics N.V.||Defibrillator with a self-test system|
|EP1852144A2 *||May 18, 1994||Nov 7, 2007||Philips Electronics N.V.||Defibrillator with a self-test system|
|EP1852144A3 *||May 18, 1994||Nov 28, 2007||Philips Electronics N.V.||Defibrillator with a self-test system|
|WO1993017349A1 *||Jan 22, 1993||Sep 2, 1993||Zmd Corp||Defibrillation discharge current sensor|
|WO2005038476A1 *||Oct 16, 2003||Apr 28, 2005||Cudmore Francis James||Non-linear dummy load for monitored ac loads|
|U.S. Classification||607/8, 324/142|