U.S. patent number 3,791,373 [Application Number 05/231,161] was granted by the patent office on 1974-02-12 for portable electroanesthesia device with automatic power control.
This patent grant is currently assigned to Southern Illinois University Foundation. Invention is credited to Edward J. McGowan, Jr., Edward R. Winkler.
United States Patent |
3,791,373 |
Winkler , et al. |
February 12, 1974 |
PORTABLE ELECTROANESTHESIA DEVICE WITH AUTOMATIC POWER CONTROL
Abstract
A portable, battery-powered, self-contained electroanesthesia
device. A signal generator provides a sinusoidal, constant
magnitude signal of fixed, preset frequency with relatively high
accuracy and without recalibration each time the device is
energized. The preset frequency characteristically produces
electroanesthetic induction in a live subject with relatively high
efficiency. An amplifier increases the power level sufficiently for
producing electroanesthetic induction of the subject. Electrodes
supply the amplified signal to tissue of the subject, there being
provision for matching the impedance of said tissue of the subject
to the amplifier for maximizing transfer of the amplified signal to
said tissue. Circuitry is provided also for monitoring and limiting
the power level of the signal supplied by said electrodes to the
tissue.
Inventors: |
Winkler; Edward R. (Carbondale,
IL), McGowan, Jr.; Edward J. (Villa Park, IL) |
Assignee: |
Southern Illinois University
Foundation (Carbondale, IL)
|
Family
ID: |
22867988 |
Appl.
No.: |
05/231,161 |
Filed: |
March 2, 1972 |
Current U.S.
Class: |
600/26 |
Current CPC
Class: |
A61N
1/36021 (20130101); A61N 1/378 (20130101); A61N
1/3603 (20170801) |
Current International
Class: |
A61N
1/32 (20060101); A61N 1/08 (20060101); A61N
1/34 (20060101); A61n 001/34 () |
Field of
Search: |
;128/1C,422 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
85,655 |
|
Aug 1965 |
|
FR |
|
1,076,286 |
|
Feb 1960 |
|
DT |
|
Other References
Buchsbaum, "Electronics World," September 1963, pp. 27-29..
|
Primary Examiner: Kamm; William E.
Attorney, Agent or Firm: Koening, Senniger, Powers and
Leavitt
Claims
What is claimed is:
1. A portable, battery-powered and self-contained electroanesthesia
device comprising:
means for generating a substantially constant magnitude signal of
substantially sinusoidal waveform at a fixed, preset frequency with
relatively high accuracy and without requiring recalibration each
time said device is energized, said preset frequency
characteristically producing electroanesthetic induction in a live
subject with relatively high efficiency;
means for amplifying said signal to a power level suitable for
producing electroanesthetic induction of the subject;
means for supplying the amplified signal to tissue of the subject
to cause electroanesthetic induction of the subject;
means for matching the impedance of said tissue of the subject to
said amplifying means for maximizing transfer of the amplified
signal to said tissue;
means for monitoring the power level of the signal supplied to said
tissue; and
means for automatically limiting the power of the signal supplied
to said tissue to a maximum level, said power limiting means being
adapted to sense the voltage applied to and the current drawn by
said live subject.
2. A portable, battery-powered electroanesthesia device as set
forth in claim 1, said preset frequency being substantially equal
to a harmonic of 700 Hz.
3. A portable, battery-powered electroanesthesia device as set
forth in claim 1 wherein the power limiting means includes means
for summing voltages which vary as functions of the voltage and the
current of the signal supplied to said tissue, means for generating
a control signal which varies as a function of the summed voltages
and which is thereby a function of the power level of the signal
supplied to said tissue, and means responsive to said control
signal for controlling the power level of the signal supplied to
said tissue.
4. A portable, battery-powered electroanesthesia device as set
forth in claim 3, said power limiting means further comprising
manually variable means for preselecting a maximum level to which
the power of the signal supplied to said tissue is limited.
5. A portable, battery-powered electroanesthesia device as set
forth in claim 3 wherein said means responsive to said control
signal comprises a field effect transistor.
6. A portable, battery-powered electroanesthesia device as set
forth in claim 4 further comprising manually variable means for
controlling the power level normally supplied to said tissue, and
manually variable means for adjusting the maximum power level.
7. A portable, battery-powered electroanethesia device as set forth
in claim 1 wherein the signal generating means comprises an
oscillator including a resistance-capacitance feedback circuit
causing oscillation at said preset frequency to supply said
sinusoidal signal and a second feedback circuit comprising a
resistance-capacitance controlled field effect transistor for
causing said signal to be maintained substantially at said constant
magnitude.
Description
BACKGROUND OF THE INVENTION
This invention relates to electrically induced anesthesia, i.e.,
electroanesthesia, and more particularly to devices for supplying a
periodically varying current to tissue of a living subject for
causing anesthesia.
It has long been proposed to produce anesthesia in human subjects
as well as in lesser animals by causing an electric current to flow
through tissue of the subject and various techniques for
accomplishing this have been under investigation for many years.
The literature is replete with many reports of such
investigations.
The use of alternating currents of various single or mixed
frequencies and of various waveforms, such as square-wave,
triangular-wave, and so forth, has been suggested. However, it has
been observed that a frequency of 700 Hz provides satisfactory
electroanesthetic induction in a human subject. The use of a
sinusoidal signal at such a frequency has been suggested in an
article by William B. Wood et al., entitled "The Cardiovascular
Effects of Cranially-Impressed Electric Currents of Anesthetic
Intensity" in Anesthesia and Analgesia Current Researches, Vol. 43,
No. 3 (May-June), 1964. It has also been observed that a sinusoidal
signal of substantially exactly 700 Hz or a multiple thereof
characteristically produces electroanesthesic induction in a
subject with relatively high efficiency. That is, less current (and
thus less power) is required to effect anesthesia at such a
frequency than at other frequencies.
Devices of an experimental nature have been constructed for
supplying signals of various waveforms and frequencies. An
electroanesthesia instrument has also been commercially available,
this instrument generating two sinusoidal signals, one of a quite
low frequency and the other of a higher variable frequency, the
signals being mixed together to provide a signal of complex
waveform which is amplified for being applied to electrodes secured
to (or embedded in) tissue of a subject.
Devices heretofore suggested or available have not been suitable
for other than laboratory or operating room use because they have
not, as a practical and realistic matter, been truly portable in
character. This is so either because such devices have required an
a.c. utility power connection (with consequent risk to the subject
of shock, etc.) or, at best, have needed heavy and cumbersome
storage batteries in the absence of utility power because of their
considerable power requirements. Thus, prior art devices have not
been self-contained, as required for true portability (and as is
important for field or emergency use).
Moreover, because the frequency supplied by such prior art devices
is subject to variation, the amount of power required to effect
anesthesia is also subject to variation to the extent that, at some
frequencies, considerable power may be required to achieve
anesthesia, further gravitating against portability. Furthermore,
this has required that the user establish by trail and error a
frequency producing the most satisfactory anesthesia.
Alternatively, recalibration of the device has been required if it
be desired, for example, to produce a signal at the highly
effective frequency of 700 Hz.
BRIEF SUMMARY OF THE INVENTION
Among the several objects of the invention may be noted the
provision of an electroanesthesia device which is truly portable in
character, which is battery powered, and which is self contained;
the provision of such a device which does not require heavy,
cumbersome storage batteries but is instead powered by small
rechargeable cells contained within the device; the provision of
such a device adapted to provide electroanesthetic induction of a
subject with high efficiency and which, for this purpose, does not
require recalibration each time it is energized; the provision of
such a device which, in use, does not constitute a hazard for the
subject; the provision of such a device which prevents excessive
power from being supplied to the subject thereby to protect the
subject; the provision of such a device which is not prone to
damage if output electrodes thereof become shorted; the provision
of such a device which employs semiconductor circuitry, which is
simply and inexpensively constructed, and which is long lasting and
reliable in operation. Other objects and features will be in part
apparent and in part pointed out hereinafter.
Briefly, a portable, battery-powered and self-contained
electroanesthesia device includes means for generating a signal of
substantially sinusoidal waveform at a fixed, preset frequency with
relatively high accuracy and without recalibration each time said
device is energized, the preset frequency being such as will
characteristically produce electroanesthetic induction in a live
subject with relatively high efficiency. The sinusoidal signal is
of substantially constant magnitude. Means is provided for
amplifying the siggnal to a power level suitable for producing
electroanesthetic induction of the subject. The device includes
means for supplying the amplified signal to the tissue of the
subject to cause electroanesthetic induction of the subject as well
as means for matching the impedance of said tissue of the subject
to the amplifying means for maximizing transfer of the amplified
signal to this tissue. The device further comprises circuitry for
monitoring the power level of the signal supplied by said means to
said tissue. Preferably, the power monitoring circuitry comprises
means for automatically limiting the power supplied to the subject
to a preset maximum level.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of circuitry of a portable,
battery-powered electroanesthesia device of the invention;
FIG. 2 is a schematic diagram of circuitry of the preferred
embodiment; and
FIG. 3 is a graph useful in explaining operation of the device;
Corresponding reference characters indicate corresponding parts
throughout the several views of the drawings.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, a block diagram illustrates major
components of a portable battery-powered electroanesthesia device
of the present invention. At 11 is indicated an oscillator, i.e., a
signal generator, providing a substantially sinusoidal, constant
magnitude signal at a fixed, preset frequency, preferably
substantially precisely 700 Hz. This frequency characteristically
produces electroanesthetic induction in a live subject with
relatively high efficiency. This sinusoidal-waveform 700 Hz signal
is provided each time the circuit is energized without any need for
recalibration of the device. Oscillator 11 is preferably solid
state in design, the output signal therefrom being supplied to a
solid state power amplifier circuit 13. Manually variable impedance
means 15 is connected between oscillator 11 and amplifier 13 for
controlling the power level of the signal supplied by electrodes to
the electroanesthesia subject 17 by suitable electrodes 19. Also
included is an impedance-matching or output transformer 21 having a
turns ratio preselected to match the effective impedance of the
tissue of subject 17 across which the electrodes are applied to the
output impedance of amplifier 13, thereby to maximize transfer of
the amplified signal to tissue of subject 17.
The circuit includes means for monitoring the power level of the
signal supplied by electrodes 19 to tissue of subject 17. The
latter means may be regarded as comprising, in a first aspect, a
current meter 23 and a voltmeter 25 which together measure and
indicate the magnitude of the current and the voltage of the signal
supplied to subject 17. Voltmeter 25 is also used to indicate the
potential of a battery power supply 27 (i.e., self-contained nickel
cadmium cells) which power the instrument. A voltmeter switch 29
selects which potential is to be measured. A conventional battery
charger circuit 31 is preferably, but not necessarily, provided for
recharging the cells from line-voltage household current.
The power level monitoring means also comprises, in a second
aspect, a provision for automatically limiting the power of the
signal supplied from amplifier 13 by electrodes 19 to subject 17.
This power monitoring means includes power sensing circuitry 33
which compares the voltage and current of the signal supplied by
the electrodes and includes also means for generating a control
signal which varies as a function of the compared voltage and
current and which is thereby a function of the power level of the
signal supplied by electrodes 19. Limiting circuitry 35 is
responsive to the control signal for controlling the power level
delivered by amplifier 13 via electrodes 19 to subject 17. A
manually variable impedance means 37 is provided for preselecting a
maximum power level to which the signal supplied by electrodes 19
is to be limited.
Referring now to FIG. 2, all of the elements to the right of the
dashed line indicated at 41 are advantageously mounted on a single,
small printed circuit board, there being suitable interconnections
between this circuit board and remaining components of the
circuitry which are not located on the circuit board, such as the
battery cells, level controls 15 and 37, as well as voltmeter 25
and ammeter 23. All components including the cells are suitably
mounted within a small conventional instrument housing of a few
inches in each dimension having a face panel on which are located
the off-on and level controls, meters 23 and 25, and suitable
terminals for connection of electrodes 19.
Battery power supply 27 is seen to constitute two sets of cells 27a
and 27b, the junction of which constitutes the circuit ground and
the other ends of which provide power supply potentials +V and -V,
respectively, at levels suitable for semiconductor circuitry to the
various portions of the circuit on the printed circuit board via
leads L1, L2 and LN.
The oscillator circuitry 11 includes a differential operational
amplifier A1 of a monolithic integrated circuit variety, such as
the commercially available Type 741. Similar operational amplifiers
used in the device are designated A2-A4. A so-called bridge-T
feedback circuit 43 is interconnected between the output and
inverting input of amplifier A1, including capacitors C1 and C2 and
resistors R1-R3. The values of these elements are chosen such that
the output of amplifier A1 delivers a sinusoidal frequency of
substantially precisely 700 Hz, resistance R3 being constituted by
a trimming potentiometer for providing fine adjustment of the
frequency to this value.
A second feedback circuit 44 for amplifier A1 causes the output
signal of amplifier A1 to be maintained substantially at the
constant magnitude. For this purpose, a diode D1 rectifies the
sinusoidal output of amplifier A1 and stores the rectified voltage
across a capacitor C4. A potentiometer R5 connected across
capacitor C4 provides at its wiper a voltage for biasing the gate
of a field effect transistor (FET) Q1, whose source and drain
terminals are connected in a circuit including a resistor R6
between the output and noninverting it of amplifier A1. The
noninverting input of amplifier A1 is also connected through a
resistor R7 to the circuit ground. FET Q1 operates in effect as a
voltage-control resistor to control the gain of amplifier A1 and
thereby to maintain its output voltage substantially at a constant
value.
The values of the elements of oscillator circuit 11 are carefully
chosen so that the output frequency will not vary more than about
.+-.5 Hz from the desired 700 Hz operating frequency over an
operating temperature of, for example, 32.degree.-140.degree. F.
Thus the 700 Hz frequency is supplied within these tolerances each
time the device is energized, without requiring any recalibration
or adjustment.
The output from oscillator 11 is supplied through a capacitor C5
and through the output power adjustment control means 15 to power
amplifier 13. Means 15 is shown to constitute a potentiometer whose
wiper provides the output signal from oscillator 11 at a
preselected magnitude across a scaling circuit comprising resistors
R9 and R10. The scaled-down output signal at the junction of these
two resistors is supplied through the source and drain terminals of
an FET Q2 to the noninverting input of operational amplifier A2. A
resistor R11 is connected between the noninverting input of
amplifier A2 and the circuit ground. The power amplification
circuit 13 comprises also a pair of power output transistors Q3 and
Q4 of complementary symmetry, Q3 being of the PNP type and Q4 being
of the NPN type. A capacitor C7 is connected between the output of
amplifier A2 and the junction of the collectors of transistors Q3
and Q4, the emitters of these two transistors being supplied with
the power supply potentials +V and -V, respectively. A resistor R8
is connected between the output of amplifier A2 and the circuit
ground.
Negative feedback for amplifier 13 is constituted by resistors R12
and R ' respectively interconnected connected between the
noninverting input of amplifier A2, the junction of the collectors
of transistors Q3 and Q4, and ground, thereby to provide amplifier
13 with a voltage gain of about 17. Thus, also, it will be seen
that transistors Q3 and Q4 are within the feedback loop. The
amplified 700 Hz sinusoidal signal is supplied through a capacitor
C11 to the primary winding of impedance-matching transformer 21.
The other side of the primary winding of transformer 21 is
connected to the circuit ground through a resistor R13 of
relatively low resistance, e.g., about 0.56 ohms, for a purpose
which shortly will be made clear.
Transformer 21 has a primary-to-secondary winding ratio of 1:3.5.
One side of the secondary of transformer 21 is connected to one of
the electrodes 19, the other side being connected through the
primary of a current transformer 43 to the other of electrodes 19.
The tissue resistance of the electroanesthesia subject 17 is
represented in the drawing as a resistor Rs connected between
electrodes 19, and may be assumed to vary over an exemplary range
of approximately 100-800 ohms. It will be understood that the
subject resistance may vary according to the type of subject (i.e.,
type of animal), the location of electrodes 19 and other factors.
Electrodes 19 may be of various cutaneous or subcutaneous types, as
those with particular expertise in electroanesthetic techniques
will be aware, the design and placement of such electrodes 19 being
outside the scope of the present description.
If the apparatus includes the battery charger circuit 31 shown in
FIG. 1 operating from line voltage, i.e., household utility
service, is important to provide isolation between the primary and
secondary windings of transformer 21 in order to ensure against a
shock hazard to the electroanesthesia subject. For this purpose,
transformer 21 is shown as including a Faraday shield 45 for
preventing stray a.c. voltages from being coupled from the primary
winding to the secondary winding, as during recharging.
Current transformer 43 is of a conventionally constructed ferrite
toroidal type, its secondary winding providing an a.c. voltage
which is proportional to the magnitude of the current flowing in
its primary winding. Connected in a circuit with this secondary
winding are a calibration potentiometer R15 and a resistor R16 and
a pair of oppositely oriented diodes D2 and D3 which rectify the
a.c. voltage appearing across the secondary winding of transformer
43 and charge respective capacitors C12 and C13. Current meter 23
is connected between the junctions of these respective pairs of
diodes and capacitors to provide a reading in milliamperes of the
current supplied to the subject.
A voltmeter circuit similary includes a calibration potentiometer
R17 and resistor R18, as well as diodes D4 and D5 and capacitors
C14 and C15. Voltmeter switch 29 is of a DP3T type and is adapted
to switch voltmeter 25 across the junctions of these respective
pairs of diodes and capacitors for indicating the potential of the
signal supplied to the subject. The positive and negative battery
supply potentials +V and -V are supplied to one side of a
respective pair of resistors R19 and R20 interconnected with switch
29, the latter being also operable to select which of these two
potentials is indicated by voltmeter 25.
Turning now to the power sensing circuitry 33 and limiting
circuitry 35, a lead L3 interconnects the top side of the primary
winding of transformer 21 with the inverting input of operational
amplifier A3 through a resistor R22 to provide a signal at this
input of the operational amplifier which is a function of the
voltage across the primary winding of transformer 21. Similarly, a
lead L4 is connected through a resistor R23 from the top of
resistor R13 to this inverting input of amplifier A3 to supply
thereto a voltage which is proportional to current through resistor
R13, and which is thus also proportional to the current applied to
the subject. The noninverting input of amplifier A3 is grounded and
another resistor R24 provides a feedback connection between the
output and the inverting input of this operational amplifier. Thus
the latter is seen to be connected as a summing amplifier which
takes, in effect, a weighted sum of the voltage and current of the
signal supplied to the primary winding of transformer 21 to
approximate the product of this voltage and current and thereby to
approximate the amount of power delivered by the device to the
subject.
The voltage at the output of amplifier A3 is therefore a control
signal which varies as a function of the voltage and current and is
thereby a function of the power level of the signal supplied by the
electrodes 19. This signal is rectified by a diode D7 and supplied
through a resistor R25 to the inverting input of comparator
amplifier A4. A resistor R26 and a capacitor C17 are connected
between the anode of diode D7 and the circuit ground and remove the
a.c. component of the signal. Circuitry for providing a reference
voltage to the inverting input of amplifier A4 comprises resistors
R27 and R29, the latter a calibration potentiometer. A resistor R28
and a zener diode D8 form a reference voltage supply that excites
the internal reference potentiometer R29 and/or the external
overload limit control 37 (to the left of the dash line 41).
Control 37 is constituted by a potentiometer whose wiper is
connected to the junction between resistor R30 and capacitor C18.
The position of this wiper accordingly determines the magnitude of
the bias voltage applied to the inverting input of amplifier A4. A
feedback connection is provided between the output and inverting
input of amplifier A4 by resistor R31. Thus, depending on the
setting of the limiting control potentiometer 37, the voltage at
the output of amplifier A4 becomes increasingly negative with
increasing power when the voltage proportional to power exceeds the
voltage from limiting control 37.
The gate of FET Q2 is interconnected through a resistor R32 to the
output of amplifer A4 and through a clamping diode D9 to the
circuit ground. Accordingly, conduction through the source and
drain electrodes of FET Q2 is limited when the output of amplifer
A4 becomes increasingly negative, the FET acting in effect as a
voltage-controlled resistor. Thus, should the power supplied by the
apparatus to the electroanesthesia subject increase beyond a
preselected maximum level determined by setting of control 37, an
increasingly negative voltage is supplied by operational amplifier
A4 to the gate of FET Q2 to reduce the magnitude of the signal
supplied to the noninverting input of amplifier A2, and thereby to
limit automatically to the preselected maximum level the power
supplied by electrodes 19.
Operation of the present device can be better understood by
referring to FIG. 3 in which the increasing effect of relaxation
and analgesia of an electroanesthesia subject are plotted as
functions of increasing frequency of a sinusoidal electroanesthesia
current for different magnitudes of current through tissue of the
subject. This graph indicates that for current of a first magnitude
I.sub.1, relaxation increases in magnitude with increasing
frequency, as shown by the solid-line curve 47, while the degree of
analgesia (insensitivity to pain) decreases with increasing
frequency, as shown by the dashed-line curve 49. A frequency
f.sub.1 may be regarded as an optimum frequency with regard to both
relaxation and analgesia, in that both relaxation and analgesia are
relatively high at this frequency. If the current be increased to a
still greater magnitude I.sub.2, relaxation also increases with
increasing frequency, as indicated by the solid-line curve 51,
while analgesia decreases with increasing frequency, as shown by
the steeply sloped dashed-line curve 53. Again, there is an optimum
frequency f.sub.2 at which both relaxation and analgesia are
optimized. Greater current through the subject requires greater
power and thereby requires greater battery capacity in a portable
device of the character described. Thus, it will be seen that
certain frequencies, i.e., 700 Hz, 1,400 Hz, and so forth, have
particularly good results, permitting electroanesthesia to be
achieved with the least amount of power. Since the power required
to effect anesthesia is minimized, small rechargeable cells are
able to power the present device for several hours of continuous
operation.
If the current supplied to the subject were to become excessive,
there could be danger to the subject. However, the power limiting
circuitry of the invention automatically limits the maximum amount
of power supplied to the subject, preventing injury. As an example,
the normal operating power can be about 150 mW, and the power under
overload conditions can be limited to no greater than about 300 mW,
for example. Of course, by changing the setting of limiting control
37, the power may be limited to some value less than 300 mW. This
limiting feature also protects the instrument in the event that
electrodes 19 are shorted together, the power being automatically
limited to 300 mW or less as determined by control 37 to prevent
damage to the instrument. If desired, an indicating device such as
a light emitting diode may be employed for signalling an overload
condition of this type.
The following example illustrates the invention.
EXAMPLE
Electroanesthesia was induced in seven mongrel dogs weighing 6-7.5
kg. using a prototype model of the present invention capable of
supplying the sinusoidal signal of 700 Hz at a potential of 12 v.
and a current of 12 ma. Cutaneous circular electrodes of 1.8 cm. in
diameter were placed bitemporally on the dogs and anesthesia was
induced with the device. The magnitudes of the current and voltage
required for loss of toe-pad reflect were recorded, and the
corresponding impedance and wattage were then calculated from these
figures for each animal. The length of time required for induction
in each case, as well as indications of smoothness or discomfort,
were recorded. It was found that, on the average, 1-1.5 minutes
were required for each animal to reach a state of anesthesia using
the device. The following table indicates the amount of power
required for each of the seven subjects:
TABLE
Corrected Dog Power (mW) 1 44.0 2 43.2 3 27.3 4 14.2 5 54.2 6 13.1
7 13.9
the average power required for these seven subjects was 27.99 mW. A
prior art device was also used to achieve anesthesia for these
seven subjects and was found to require 4-8 minutes on the average
to achieve the same state of anesthesia as the device of this
invention, and required a substantially higher average power.
In view of the above, it will be seen that the several objects of
the invention are achieved and other advantageous results
attained.
As various changes could be made in the above constructions without
departing from the scope of the invention, it is intended that all
matter contained in the above description or shown in the
accompanying drawings shall be interpreted as illustrative and not
in a limiting sense.
* * * * *