Note: Descriptions are shown in the official language in which they were submitted.
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SAFETY MONITOR CIRCUIT FOR AN ECT DEVICE
Background Of The Invention
1. Field of the Invention
The present lnvention relates to medical apparatus and
methods and more particularly to electroconvulsive therapy
(ECT) apparatus and method for preventing an excessive or
insufficient stimulus dosage.
2. Description of the Related Art
In electroconvulsive therapy (ECT), using "bitemporal"
electrode positioning, generally two electrodes are applied to
the temple of the patient during the treatment session. One
electrode is positioned on the temple's left side and the
other on the temple's right side. A small electric current,
called the "stimulus dosage", is applied for less than ten
seconds between the two electrodes. Alternatively, the
electrodes may be positioned anterior bilaterally or
unilateral. Only a small portion of the current reaches the
brain because most is deflected by the skull.
It has recently been shown that when a~ ;nictered
according to accepted st~n~rd of practice (American
Psychiatric Association, APA, 1990). Electroconvulsive
therapy (BCT) is a safe procedure that does not have a
measurable risk of brain injury. The APA standard of practice
includes a limitation of the stimulus dosage a~;nictered to
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the patient, because of the expectation that unnecessarily
high stimulus dosages may cause adverse effects to the
patient. To accomplish the delivery of a stimulus dosage
within operator specifications, i.e., the stimulus dosage
determined by the atte~ing physician, existing ECT devices
rely on a ~Al;hration, or test, conducted prior to initiation
of the stimulus or during periodic maintenance checks on the
ECT device. Once the stimulus dosage has been initiated,
delivery of an accurate dose, for example, within the APA
standard, has relied solely on the circuits of the ECT device
that generate the stimulus. There has been no separate
circuit or device to monitor and measure the stimulus dosage
during its application, and to terminate the stimulus in the
event it exceeds the operator's specification, i.e., the
operator's setting of the dosage on a dial of the ECT device.
In the event of failure of an electronic component it is
possible for existing ECT devices to deliver an electrical
stimulus dose that substantially exceeds the operator's
specification. It is also possible that such a dosage would
exceed the ~; indicated by a national or international
agency that publishes, or could publish, stAn~Ards for ECT
devices, e.g., the IEC - International Electrotechnical
C~ ;~sion 601-2-14; the APA - American Psychiatric
Association; the FDA - Food and Drug A~n; n;stration. Such an
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excessive dosage may inadvertently, and unnecessarily, expose
the patient to a dose that exceeds the published limitations
for ECT devices.
A "worst-case" scenario would be the exposure of the
patient to line current, as might occur in failure of the ECT
device's transformer, for example, a transformer short circuit
due to insulation breakdown. Although the likelihood of such
an occurrence is extremely remote, such a possibility must
nevertheless be considered because of the life and death
nature of such exposure.
Existing test methods employed to evaluate the safety of
the stimulus prior to ECT are limited to measuring the skin
impedance of the patient by applying impalpable electrical
trickle currents to the patient's skin. However, such skin
impedance test circuits cannot prevent the patient from
receiving an excessive electrical dosage that may be delivered
in the event of component failure in the ECT device, because
such skin impedance test circuits do not monitor the actual
stimulus.
In ECT, the physician determines the stimulus dosage,
i.e., the length and strength of the applied current. He
takes into account such factors as the patient's age, size,
physical condition and prior history of ECT treatments. The
seizure threshold systematically increases with age. The
physician may, with presently available apparatus, reasonably
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and accurately select the desired electrical duration. For
example, in the "Thymatron-DGx" ECT instrument (TM of
Somatics, Inc., Lake Bluff, Illinois) the stimulus may be
selected to be a brief series of electrical square waves,
providing a constant current of 0.9 amps limited to S00 volts,
consisting of 60-140 bipolar pulses per second of 1 msec
width, which is adjustable, by the physician, 0.1 - 8.0 second
in duration. Alternatively the dosage may be administered in
groups of pulses, pacing them over a period of up to 8
seconds.
Generally the physician will determine the stimulus
dosage and set that selection in the ECT device by setting a
stimulus dial. The ECT device, in the case of the
"Thymatron-DGx" device, has factory preset pulsewidth,
frequency and duration which corresponds to each stimulus dial
setting. Alternatively, the physician may elect to set other
pulsewidths, frequencies and durations within the range 30-70
Hz and 0.5 to 1.5 msec.
In U.S. Patent 5,269,302 to Swartz and Abrams, an ECT
device includes a special-purpose ele~LL~~ ograph (EMG) to
detect muscle activity. In U.S. Patent 4,873,981 to Abrams
and Swartz the ECT device includes a system to automatically
monitor and display the occurrence and duration of an induced
EEG seizure. In U.S. Patent 4,709,700 to Hyrman an ECT device
uses short pulses of 20-100 microseconds and unidirectional
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electric direction. The Hyl -n patent, incorporated by
reference herein, discusses the t~hn;ques of "ergometry"
(measurement of ECT dose in pulses) and "coulometry" (total
charge which flows during treatment).
Summary Of The Invention
The present invention presents a method and system to
automatically monitor and measure the cumulative stimulus
dosage of an ECT device. The dosage produced at the output
terminals of an ECT device, during stimulus delivery, is
measured by a separate excessive output control circuit which
is preferably integrated into the ECT instrument. A known
portion of the stimulus from an output driver is first passed
through a pulse transformer or opto-isolator. The cumulated
dosage of that stimulus is measured by a completely separate
analog or digital excessive output control circuit. Since the
excessive output control circuit is completely separate from
the main circuitry of the ECT device, except for its power
supply, any fault in the main circuitry, such as its
microprocessor CPU, will not affect the separate excessive
output control circuit, since it has its own microprocessor
CPU, etc. The stimulus is automatically compared to the
stimulus dose set by the operator using a percent energy
selector, which is preferably a dial on the ECT device.
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In the event of an "excessive dosage" further stimulus
delivery is automatically blocked and audible and/or visual
signals are activated. An "excessive dosage" is when a
predetermined increment (e.g., 5%, or 25 millicoulombs [mC] or
5 Joules [J~) over the specified dosage has been delivered.
If the stimulus dosage which is actually delivered is less
than a predetermined threshold (below the operator's
specification for the stimulus dosage), a different set of
audible and/or visual signals are triggered.
Objectives And Features Of The Invention
It is an objective of the ECT insL,I -nt to provide a
stimulus dosage that conforms with reasonable accuracy (e.g.,
within 5%, 25 mC, 5 J) to the specification set by the
operator using the ECT instrument's controls.
It is a further objective of the present invention that
the physician may directly set the electrical charge of the
stimulus dosage, in millicoulombs (mC), and that dosage will
be delivered within a selected limit, for example, 5% of the
selected dosage.
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Brief Description Of The Drawings
Other objectives of the present invention will be
apparent from the following detailed description, which should
be taken in conjunction with the accompanying drawings. In
the drawings:
Figures 1 and 2 are block circuit diagrams of a preferred
embodiments of the present invention; and
Figures 3 and 4 are block circuit diagrams of an
alternative lower-cost circuits of the present invention.
Detailed Description
In accordance with the present invention there is
provided a system and method in ECT to automatically measure
and monitor the cumulative amount of electrical dosage given
to a patient in each ECT treatment session. If the amount of
dosage is in excess of the amount selected by a predetermined
limit, the application of the dosage is ; -~;ately and
automatically halted. In addition, the att~;ng physician is
warned of the excessive dosage by a warning light and/or an
audio signal. On the other hand, if the dosage is below the
selected dosage by a predetermined limit, the physician is
warned by a different light and/or audio signal. Preferably,
in that case, the percentage of dosage that has been applied
is displayed; for example, a display may say "20%", indicating
20% below the selected dosage.
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Preferably the ECT system of the present invention is
incorporated as part of an ECT device; however, it may be
possible to retrofit it into some existing ECT devices,
depending on their circuitry.
The limits may be set in a number of ways. For example,
a limit may be set as being plus and minus 5% of the selected
dosage. If the dosage is 100 J (Joule) then the 5% limit
would be 5J and an excessive dosage would be 105J and an
insufficient dosage would be 95J or less. Alternatively, the
plus and minus limits may be set as an arbitrary amount of
charge dosage, for example, plus and minus 25 mC (25
milliCoulombs) over a range of from 25 mC to 500 mC.
In general, the amount of electrical power that is
generated by the ECT device and applied to the patient is
measured by sampling the power furn;~:hl~ at the output
electrode of the device. Such sampling is preferably
perf~ormed in a circuit parallel to the output circuit.
The present invention provides circuitry to monitor the
stimulus dosage of electrical current as it is actually
applied to the patient. It operates in "real time"
~ ;ately) thereby automatically limiting the dosage, to
within a predetermined amount, of the dosage specified by the
operator, e.g., the atten~;ng physician.
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The circuitry for two alternative "high end" alarm and
control circuits is shown in Figures 1 and 2. The bitemporal
electrodes 10 and 11 are adapted to be removably attached to
the temple of the patient at the left and right sides. A
single-double-pole double-throw (DPDT) relay switch 12
connects the lines leading to the electrodes 10 and 11 either
to the GuL~uL lines 13 and 14 or to the dummy load line 15
having a 200 ohm resistor 16. The switch 12 is operated by
the output relay driver 17.
The output driver 20, which is generally the secondary
winding of a transformer, provides the current for the
stimulus dosage generally as a sine wave or rectangular waves.
The output driver 20 is controlled by the main "CPU" (Central
Processing Unit) 22 which preferably is a solid-state
integrated circuit ("IC") and is preferably a microprocessor
such as a Motorola 68306 (TM of Motorola, Inc., Schaumburg,
Illinois). The main CPU 22 is connected to the Percent Energy
Selector 23 which preferably is a dial of the ECT device. The
dial is set by the operator to select the desired stimulus
dosage.
In the embodiment of Figure 1 an opto-isolator 24 is
connected in parallel to line 14, a suitable opto-isolator
being Siemens IL300. The output of the opto-isolator 24 is to
amplifier 25.
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In the embodiment of Figure 2 a primary winding 21 of
pulse transformer 24 provides a sample of the current on line
14 which is amplified by amplifier 25.
In the embodiments of Figures 1 and 2 the ouL~uL of
amplifier 25 is to Fast A/D (Analog-Digital converter) 26.
The Fast A/D 26 is connected for data transfer ("Data"),
address information ("Address") and control ("Control") to
High Speed Microcontroller 27, for example, a Motorola 68306.
The microprocessor 27 enables (controls the Alarm LED (Light
Emitting Diode) and warning tone 28 (audio generator).
In the embodiments of Figures 1 and 2 the electrical
ouL~L at the output driver 20 is in the form of a regular
waveshape, generally a sine wave or rectangular wave. That
ouL~uL waveform is sampled at a high rate, for example,
100,000 times a second, and the analog samples are converted
to digital data by the Fast A/D converter 26. The digital
data (Data) is transferred from Fast A/D 26 to a high-speed
programmable microcontroller 27 having an internal RAM (Random
Access Memory). The RAM is programmed with a look-up table in
which the selected dosage, selected by Percent Energy Selector
23, has been entered and a corresponding different selected
limit for each ~elected dosage has also been entered.
Preferably the selected limit is automatically calculated for
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each selected dosage by a programmed algorithm entered into
the microprocessor and then the selected limit is entered into
the RAM look-up table.
~ If the limit is exceeded the microcontroller 27 will
generate an inhibit control signal, which is the "output
disable" signal on line 40 to relay driver 17, to terminate
the dosage. Such termination can be accomplished in less than
l/lOOth of a second so that the excess dosage would be less
than 1% over the selected limit. In addition, that control
signal, or a subsequent signal generated by the
microcontroller 27, will activate the warning device 28 to
call the attending physician's attention to the excessive
dosage. Preferably a warning lamp is lit and/or an audio
signal, such as a buz~, is produced.
If the selected dosage is not reached, the ECT device
will automatically notify the physician that the dosage was
insufficient and will display the amount of the insufficiency.
Preferably a different warning light and/or audio sound is
used and the amount of insufficiency is displayed on a
numerical display panel of the ECT device and/or printed by a
connected alphanumeric printer.
Two "low end" alternatives (shown in Figures 3 and 4~ to
the "high end" use of a high-speed A/D converter and high-
speed microprocessor, as in Figures 1 and 2, use an oscillator
which is connected in parallel to the output electrodes of the
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ECT device. In the circuit of Figures 3 and 4, an oscillator
(VCo - Voltage Controlled Oscillator) is configured to act as
a voltage-to frequency converter in which a rising voltage is
measured and converted to a higher frequency rate. The pulses
from the VCO (Voltage Controlled Oscillator) are connected
through a divider 67 to a counter 68. The output of counter
68 is processed by a low-speed microprocessor. The use of a
RAM look-up table, the control signals and the warnings are
preferably the same as in the prior embodiment.
The circuitry for a "low end" alarm and control circuits
are shown in Figures 3 and 4. The bitemporal electrodes 50
and 51 are adapted to be removably attached to the temple of
the patient at the left and right sides. A double-pole
double-throw (DPDT) relay 52 connects the lines leading to the
electrodes 51 and 52 either to the o~uL lines 50 and 51 or
to the dummy load line 55 having a 200 ohm resistor 56. The
switch 52 is operated by the output relay driver 57.
The output driver 60, which is generally the secondary
winding of a transformer, provides the current for the
stimulus dosage. The output driver 60 is controlled by the
main "CPU" (Central Processing Unit) 61 which preferably is a
solid-state integrated circuit ("IC") and is preferably a
microprocessor such as Motorola 68306. The main CPU 61 is
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connected to the Present Energy Selector 63 which preferably
is a dial on the ECT device. The dial is set by the operator
to select the desired stimulus dosage.
In the embodiment of Figure 3 an opto-isolator 73 is
connected in parallel to line 54, a suitable opto-isolator
being Siemens IL 300. The output of opto-isolator 73 is to
amplifier 55.
In the embodiment of Figure 4 the primary winding 61 of
pulse transformer 64 provides a sample of the current on line
61 which is amplified by amplifier 65.
In the embodiments of Figures 3 and 4 the output from
amplifier 65 is to VCO (Voltage Controlled Oscillator) 66
whose output is to divider 67. The divider 67 is connected to
counter 68 which is controlled over line 69 from CPU 62. The
counter 68 is connected to a low-speed microcontroller 71, for
example, Intel 8051 (TM, Intel) which also is connected to
Percent Energy Selector 63. The output 71 is to the Alarm 72,
which preferably is an LED (Light Emitting Diode) and a
warning tone generator.
The circuits are provided with a manually operated test
alarm switch (41 in Figures 1 and 2; 75 in Figures 3 and 4)
and a manually operated on-off start of treatment switch (42
in Figures 1 and 2; 76 in Figures 3 and 4).
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