U.S. patent number 3,747,605 [Application Number 05/190,750] was granted by the patent office on 1973-07-24 for defibillator and method and apparatus for calibrating, testing, monitoring and/or controlling a defibrillator or the like.
This patent grant is currently assigned to William Beaumont Hospital. Invention is credited to Kenneth J. Cook.
United States Patent |
3,747,605 |
Cook |
July 24, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
DEFIBILLATOR AND METHOD AND APPARATUS FOR CALIBRATING, TESTING,
MONITORING AND/OR CONTROLLING A DEFIBRILLATOR OR THE LIKE
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 then integrated 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.
Inventors: |
Cook; Kenneth J. (Oak Park,
MI) |
Assignee: |
William Beaumont Hospital
(Royal Oak, MI)
|
Family
ID: |
22702612 |
Appl.
No.: |
05/190,750 |
Filed: |
October 20, 1971 |
Current U.S.
Class: |
607/8;
324/142 |
Current CPC
Class: |
A61N
1/3937 (20130101) |
Current International
Class: |
A61N
1/39 (20060101); A61n 001/36 () |
Field of
Search: |
;128/419D,419R,421,423
;324/103,140,141,142 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
969,659 |
|
Sep 1950 |
|
FR |
|
1,076,286 |
|
Feb 1960 |
|
DT |
|
Primary Examiner: Kamm; William E.
Claims
I claim:
1. 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.
11. 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
voltage excursion, and wherein said indicator means is responsive
to said sixth electrical signal to provide an indication of said
peak level.
14. The analyzer circuit set forth in claim 13 further comprising
detector means responsive to said first component signal 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.
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 indicator means to store said
fifth electrical signal in response to said sixth electrical
signal.
16. The analyzer circuit set forth in claim 10 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 the connection between said
input terminals and said output terminals.
17. The analyzer circuit set forth in claim 1 further comprising
reference means for setting a predetermined maximum 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 responsive to 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 in synchronism with
said first and second excursions, respectively, of said one output,
first electronic switch means coupled between said multiplication
circuit means and said 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 said input 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 independent 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 representing energy
transferred to said patient during even numbered pulsations of said
power signal, and wherein said comparator means further comprises
means for summing said first and said second component signals to
provide said second electrical signal for comparison against said
predetermined energy level.
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 cardiac condition
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 whereby energy is
transferred to said load in pulsations, sensing at least one of
said outputs, determining in response to at least one of said
outputs the power transferred to said load over a series of power
pulsations, measuring energy transferred to said load during odd
numbered pulsations in said series of power pulsations 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 pulsations.
Description
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 electrocardiogram (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 nonsurgically, the defibrillator voltage is applied via
paddle-type electrodes across the patient's 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 total energy. 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 damping
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
patient 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 initial treatment. 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 to
the 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 2;
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 10 has its output connected
via leads 12, 14, an electronic shunt switch 16, voltage and
current sensing circuits 18 and leads 12', 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
patient's 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.
Alternatively, 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 short-circuits 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.sub.1 and the output voltage V.sub.1. 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.sub.1 in FIG. 3a. Although the
voltage waveform V.sub.1 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.sub.1 will be in phase with and correspond to the voltage
waveform V.sub.1. 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.sub.1 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.sub.1 is illustrated as positive but it will be
understood that the present invention operates effectively
regardless of the assumed polarity of the initial 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.sub.10
and V.sub.11 (FIG. 1), of the input signals. The signals applied to
amplifier 28 and hence the signal V.sub.10 represent the voltage
V.sub.1 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.sub.11 represent the current
I.sub.1 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 double-pole,
double-throw switch 34. The output of amplifier 28 is also fed to
an absolute value amplifier 36 whose output signal V.sub.2 (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.sub.10 from amplifier 28 so that
the signal V.sub.2 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.sub.2
corresponds to the waveform of the voltage V.sub.1 (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.sub.12. With
the input to module 32 taken from contacts 34a, 34b, the output
signal V.sub.12 represents the instantaneous power output (V.sub.1
times I.sub.1), where V.sub.1 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.sub.12 will be
proportional to the instantaneous power, i.e., V.sup.2 divided by R
where R is the resistance of resistor 23. The output signal
V.sub.12 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.sub.5, V.sub.6 (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.sub.5,
V.sub.6, in response to an input signal V.sub.3 (FIG. 3c) developed
by a threshold detector 48 from the output signal V.sub.2 of
amplifier 36. The signal V.sub.3 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.sub.2 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.sub.3 is substantially equal to
that of its associated half cycle in the signal V.sub.2. Hence the
leading edge of each pulse 47 in the signal V.sub.3 is synchronized
substantially with the zero crossing in the original output voltage
in V.sub.1. As exaggerated in FIG. 3c, the decreasing peak
amplitude of successive half cycles of the signal V.sub.2 will
cause a slight reduction in the width of successive pulses in the
signal V.sub.3. 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.sub.2 corresponding to the peak value 31 of
voltage V.sub.1. 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.sub.2
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.sub.2 of the amplifier 36 drops below the
threshold level 49. Hence the outputs V.sub.7, V.sub.8 (FIGS. 3g,
3h, respectively) represent the total energy in the odd and even
half cycles, respectively. When the output V.sub.2 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-and-hold
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 64 to 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.sup.2
divided by R.
It is also noted that the integrated signals V.sub.7, V.sub.8 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.sub.7 and V.sub.8 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.sub.7 and V.sub.8
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 button 70. Push
button 70 is closed momentarily before operating defibrillator 10
to light a reset indicator 72 and ready control 46 for the signal
V.sub.3. Upon operation of defibrillator 10, the leading 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.sub.4 (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.sub.4 is slightly greater than the time
duration of the longest expected half cycle of signal V.sub.2. So
long as the peak half cycle voltage in signal V.sub.2 exceeds the
threshold 49, timer 76 will not time out. When the peak level of
signal V.sub.2 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 the strobe signal, the MOSFET turns off to again isolate
the sample-and-hold circuits 50, 52, 58, 60 from their respective
inputs to hold the sample on the capacitor for reading via switch
62 and meter 66. Conventionally, the capacitors in the
sample-and-hold circuits 50, 52, 58, 60 may be coupled to switch 62
via a high input impedance amplifier so that 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.sub.5, V.sub.6 on lines
39, 41 to alternately operate switches 38, 40. Switches 38, 40 are
preferably MOSFETS 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.sub.5 and V.sub.6. The pulses of waveform
V.sub.5 are coextensive with the odd numbered half cycles of
waveform V.sub.1 and the pulses of waveform V.sub.6 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.sub.1 to couple the signal V.sub.12 to
integrator 42 during odd (positive) half cycles of V.sub.1 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.sub.7 and V.sub.8 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.sub.1. The magnitudes of signals
V.sub.7 and V.sub.8 increase in increments of decreasing size until
the amplitude of voltage V.sub.1 becomes so low that the amplitude
of voltage V.sub.2 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.sub.3 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.sub.1 and integrator 44 the even numbered half cycles. Because
amplifier 36 produces only a positive output independent of the
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.sub.2, the
peak magnitude of voltage V.sub.1 is detected independent of its
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. 1, 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.sub.10 is connected to absolute value
amplifier 36. As in the circuit of FIG. 1, amplifier 36 feeds the
rectified signal V.sub.2 (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.sub.3 (FIG. 3e) which is fed
to a digital control 46 and an integrator 56 (FIG. 1). Module 32
squares the signal V.sub.2 to develop the signal V.sub.12 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.sub.1, P.sub.2 P.sub.3 in FIGS.
5a, 5b, 5c, respectively. All of the pulses in the pulse train
P.sub.1, 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.sub.1 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.sub.1
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 P.sub.1 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 the
sample-and-hold circuits 50, 52, 58, 60. Since the energy in the
pulse train from generator 114 and hence the 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.sub.2 as compared to
pulse train P.sub.1, meter 66 can be calibrated at twice the energy
level, and similarly at three times the energy level with pulse
train P.sub.3. 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 corresponding to switch 112 in lines 12, 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.sub.1 times I.sub.1
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 66 has 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
23 is again connected across leads 12', 14' by closing switch 25.
For example, as indicated earlier, commercially available
defibrillators typically have a total energy setting on knob 24.
Hence the operator can set a desired total energy level on
defibrillator 10 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 given odd or 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 the test 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.sub.1 divided by the resistance R of resistor 23. In the dashed
line position of switch 34, the odd and even half cycle energy will
be determined based on the computation of multiplying the voltage
V.sub.1 across resistor 23 by the current I.sub.1 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 10 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.sub.1 times I.sub.1. At the end of a treatment, the
operator can obtain useful information for subsequent treatment by
sequencing switch 62 to read the values of peak voltage and time
duration and positive and negative half cycle energy. As indicated
earlier, the present invention also contemplates four separate
meters to continuously monitor the information in the
sample-and-hole circuits 50, 52, 58, 60.
When operating in the control mode, potentiometer 108 is set to a
position corresponding to 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.sub.2 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 control 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
patient's chest, the total applied energy is typically in the range
of from 100-400 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 to the patient. With
experience and 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.sub.1 times I.sub.1 (FIG. 1) or
V.sub.1.sup.2 /R (FIGS. 1 and 4) could also be based on
I.sub.1.sup.2 R by simply squaring the current signal at amplifier
30 (FIG. 1). However, power measurement based on V.sub.1 times
I.sub.1 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.sub.12, although switching according to the voltage
V.sub.3 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.
* * * * *