Note: Descriptions are shown in the official language in which they were submitted.
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The present invention pertains to the field of tissue
stimulators. In particular, the invention pertains to an improved
tissue stimulator pulse generator in which the operation is
controlled by the user through a keyboard, which controls a
microprocessor which in turn controls the output pulse generator.
Tissue stimulators have gained wide acceptance in the
field of medicine for the treatment of chronic, intractable pain.
Tissue stimulators include electrical circuits for generating
electrical pulses, and leads and electrodes which convey
electrical pulses to the affected part of the body. In some
cases the entire tissue stimulator system is intended to be
implanted within the body. In other cases, the pulse generating
circuitry is contained in a box or package externally of the
body, usually adapted to be worn or carried by the patient.
Electrical leads connect from the pulse generator to electrodes
which are in contact with the body. In the case of transcutaneous
tissue stimulators, the electrodes have a significant surface area
in contact with the skin and are held in place by adhesives, etc.,
over the affected areas. In other cases, the leads are introduced
through the skin to an implanted electrode, for example, along
the spinal cord. In either case the electrical impulses travel
through the skin or body tissues and produce the effect of
relieving the sensation of pain. Controls are usually provided
on the pulse generator to control the amplitude of the output
pulses, and possibly other parameters to enable adjusting the
device for optimum results. Tissue stimulators have achieved
widespread acceptance because of their ability to deal with pain
without the use of drugs and their possible harmful side effects.
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Most adjustable prior art tissue stimulators use
potentiometers to control the output pulse amplitude. The patient
will typically turn the apparatus on and off for intervals of
time, and adjust the setting of the amplitude potentiometer as
required according to changes in the amount of perceived pain,
variations in the electrical coupling efficiency between the
electrode and skin, and various other factors.
These types of prior art devices are subject to a
certain disadvantage in operation, in that when the patient turns
the device on, there is a possibility that the output potentiometer
setting from the previous usage may be too high for the present
usage, resulting in an unpleasant sensation. This requires the
patient to quickly try to locate the control potentiometer or off
switch to correct this situation. Since most devices are designed
for multiple channel operation, it may be difficult under those
circumstances to locate the output level control potentiometer
for the correct channel quickly.
Another problem with potentiometer controls is their
relatively poor resolution which makes it difficult for a person
to make fine adjustments to achieve optimum results.
The present invention overcomes those difficulties by
providing an improved keyboard-operated, microprocessor-based
tissue stimulator which reduces output amplitude to zero, or to a
safe, low value, each time the device is turned off. When it is
subsequently turned on, the patient can gradually turn up the
output to the desired level. In this manner, the unpleasant
sensation sometimes produced by prior art tissue stimulators due
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to turn-on at too high an output level is avoided.
Thus, in accordance with a broad aspect of the invention,
there is provided a tissue stimulator of the type comprising a
housing adapted to be worn or carried by a user of the tissue
stimulator, a controlled pulse generating circuit means operable
for producing output stimulating pulses having amplitude times
controlled in response to control signals received by the pulse
generating means, user-actuable switch means for commanding
changes in output pulse amplitude, and a user-actuable stop switch
for discontinuation of output pulses characterized by: micro-
processor control means operative in response to the user-actuable
switch means for providing control signals to said pulse generat-
ing means to produce periodic output stimulating pulses, said
microprocessor control means responsive to cause a change in
output pulse amplitude in response to a command from the user-
actuable switch means, and further operable to reduce output pulse
amplitude prior to resumption of output pulses.
According to another aspect of the invention, a large
prominently placed OFF switch is provided on the tissue stimulator
unit to permit the patient to turn the device off instantly if it
should become necessary to do so for any reason.
According to another aspect of the invention, a control
keyboard is provided with a switch for automatically switching the
microprocessor to an alternate form or mode of stimulation, i.e.
for example a low-rate burst mode.
According to another aspect of the invention, keyboard
controls are provided for operating in con~unction with the
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microprocessor controller, for incrementing or decrementing
output pulse amplitude, with changes being controllable by high
resolution increments.
Brief Description of the Drawings
In the drawing, Figure 1 is a view in perspective of
a tissue stimulator pulse generator having a control keyboard
according to the present invention;
Figure 2 is a block diagram of the keyboard-controlled
microprocessor-based tissue stimulator of the present invention;
and
Figures 3A and 3B are flow charts illustrating the
operation of the tissue stimulator of Figure 2.
Detailed Description of the Preferred Embodiment
In Figure 1, reference 10 generally designates a tissue
stimulator according to the present invention. Stimulator 10
includes a housing 11 which contains the pulse generating and
control circuitry, described below. The preferred embodiment
shown is a two channel device and it includes a pair of output
terminals 12 and another pair of output terminals 13. These
output terminals can take the form of sockets which receive mating
plugs on the ends of electrode leads. Stimulator 10 typically
would include a belt clip (not shown) or other means as is
generally known in the art for enabling a patient to wear the
device. In use, electrodes (not shown) as are generally known in
the art would be applied to the affected areas of the body for
which treatment is desired, and the leads thereof connected into
terminals 12 and 13, so that the device can provide tissue
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stimulation to the affected areas.
Stimulator 10 includes a keyboard 15 which includes a
number of separate controls. These include an OFF switch 16, and
ON switch 17, a LOW RATE switch 18, and channel output control
switches 20-23. Switch 20 is labeled with appropriate indicia for
increasing channel one output, and switch 21 is labeled for
decreasing channel one output. Similarly, switches 22 and 23 are
labeled for increasing and decreasing, respectively, the channel
two output. The preferred embodîment shown is a two channel
device; however, it will be understood that the invention is also
equally applicable to stimulators having a lesser or greater
number of channels. The keyboard switches can be of any type,
for example, membrane switches, discrete switches with separate
push buttons, etc., as the type of switch is not critical to the
present invention.
The preferred form of the invention uses a sliding
keyboard cover 25 for protecting the switches against inadvertent
actuation. Briefly, in one position the cover provides access to
all switches for adjusting settings. In the protective position,
the cover blocks all switches but the OFF switch 16. While
preferred, the sliding protective cover is not necessary to the
practice of the present invention.
Referring now to Figure 2, the circuitry for the tissue
stimulator is shown in block diagram form. The microprocessor
includes a central processing unit (CPU) 30 and a read only memory
(ROM) 31 which may or may not be on the same chip as CPU 30,
depending upon the manufacturer of the microprocessor. Keyboard
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15 and the various switches thereof are in data communication with
CPU 30 as indicated by data bus 32, except that ON switch 17
connects to flip-flop 34 by lead 35. ROM 31, which contains the
program instructions, is also in communication with CPU 30, via
data bus 33. A battery or other power supply is provided within
the device for powering the control and output circuitry, but it
has been omitted from Figure 2 for purposes of clarity. Flip-flop
34, which remains permanently powered, but which draws very little
current, is connected for switching power from the battery to the
various circuits. It is set by ON switch 17 and reset to power-
down by CPU 30, in response to actuation of OFF switch 16.
CPU 30 communicates with a pulse output circuit 40 via
a plurality of data lines represented by data line 41 for channel
one, or data line 42 for channel two. Circuit 40 contains
separate output circuits for the two channels, or alternatively,
a single output circuit and switching devices for connecting it
successively to the separate output terminals for the channels.
The design of the pulse output circuits is conventional and there-
fore not shown in detail. The preferred form of the invention
uses the type of output circuit 40 which controls the pulse output
amplitude according to the width of the control pulse applied.
This can be done, for example, with the type of output circuit
that uses stored energy in an inductor to provide the output
energy. Control pulse 41 controls the build-up of current within
the inductor, and at the termination of the control pulse, the
stored energy from the inductor is transmitted out the output
terminals.
The operation of the tissue stimulator will now be
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illustrated with the aid of the program flow chart Figures 3A and 3B for the
program used in the microprocessor.
In Figure 3A, step 50 is the start of the program, which is reached
by turning on the stimulator by activation of ON switch 17. At step 51,
program parameters are initialized, and in particular the amplitudes are set
to zero ~O) output. Alternatively, they could be set to a safe nominal value.
Also at step 51, the rate control is returned to "normal", in case the device
had previously been operating in "low rate" mode.
Control then proceeds to step 52, at which the rate flag is checked.
If the "low rate" switch 18 has been depressed, the rate flag will be set
(from step 66 below), and control will branch to step 53. Step 53 is a pro-
gram delay during which the microprocessor counts output pulses and provides
delays, so as to provide the desired interval between output pulse bursts.
After step 53, or in the event that rate flag 52 was not set, control proceeds
to step 54, at which it is determined whether a change in amplitude is being
requested for channel one. This would be true if the patient were depressing
either switch 20 or 21 to increase or decrease channel one output. If so,
control branches to step 55, where it is determined whether an increase or
decrease is called for. The appropriate increase or decrease is taken care
of at steps 56 or 57. An internal register within the microprocessor used
as a counter has a count which determines the pulse width output from the CPU
on line 41 to the pulse output circuits. This counter is either incremented or
decremented at
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step 56 or 57, respectively,
Steps 60-63 correspond to steps 54-57, but apply to
channel two. If either the channel one or channel two change is
being called for, after incrementing or decrementing the
appropriate register, control passes via branch 64 to the output
routine beginning at step 70. Otherwise, control proceeds from
step 60 to step 65 at which it is determined whether the "low
rate" switch 18 is being depressed. If so, the rate flag is set
at step 66, and control passes to branch 64. If not, step 67
determines whether the OFF switch 16 is being depressed. If so,
step 68 shuts off power via circuit 34 to the microprocessor and
output circuits to save power.
In the output routine, at step 70, the channel one
output pulse is generated. Specifically, the CPU puts out a
control signal on lead 41 having a duration determined by an
internal counter for channel one. This is the counter-register
whose count can be incremented or decremented at steps 56 or 57,
above. The output pulse width from the CPU determines the tissue
stimulator output pulse amplitude for channel one, as previously
described.
The channel one and two outputs are offset from one
another by delayed times, steps 71 and 73. Step 71 is the delay
time between the channel one and channel two outputs, while step
73 is the delay time between the channel two and channel one
outputs. Delays for steps 71 and 73 are also determined by
counter-registers within the CPU. In the preferred embodiment,
these delays are adjusted in cooperation with the basic program
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execution speed of the device, so that the microprocessor will
proceed through the normal operating loop at the desired speed,
for example 85 times per second. This establishes the basic
output pulse repetition rate of the device.
Also in the preferred embodiment, delay time 71 is
altered at the same time that output pulse width 70 is altered,
at step 56 or 57, so as to maintain the total times of steps 70
and 71, a constant value. Thus, if the time for step 70 is
increased in response to actuation of switch 20, the delay tirne
at step 71 will be correspondingly decreased. The same thing
holds true for steps 72 and 73.
The low rate mode, which is believed to cause the body
to produce its own morphine-like pain killers, applies bursts of
pulses, separated by delay intervals. In low rate mode, step 53
of the flow chart, output pulses are counted, and after seven
pulses per channel, a delay is executed, then seven further pulses
are delivered, with three groups of seven pulses being produced
each second.
The increment-decrement control of output amplitude has
several advantages as compared to a potentiometer. The finest
resolution practically achievable with pGtentiometers is approxi-
mately 3% at best, and probably much worse than that. This makes
it difficult for a person to make fine adjustments to obtain
optimum output. The increment-decrement control of the present
invention provides resolution steps of 1% or less, and can be
programmed to as small steps as desired. Also, potentiometers
have the possibility of providing unpleasantly high outputs almost
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instantaneously, if the control knobs are moved or jerked too
high. The increment control of the present invention takes place
at a predictable smooth rate under program control, even if the
increase switch is inadvertently pushed. Potentiometers do not
permit practical use of a "panic" off switch because of the
built-in memory effect of the potentiometer which would result in
the same output level upon resumption of operation, unless the
user remembered to turn them down. This could provide an
unpleasantly high output level when the unit is restarted. This
effect is avoided in the present invention, by the automatic
reduction of output levels upon re-start.
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