U.S. patent application number 10/245992 was filed with the patent office on 2003-02-06 for low frequency magnetic neurostimulator for the treatment of neurological disorders.
This patent application is currently assigned to NeuroPace, Inc.. Invention is credited to Fischell, David R., Upton, Adrian R. M..
Application Number | 20030028072 10/245992 |
Document ID | / |
Family ID | 24618944 |
Filed Date | 2003-02-06 |
United States Patent
Application |
20030028072 |
Kind Code |
A1 |
Fischell, David R. ; et
al. |
February 6, 2003 |
Low frequency magnetic neurostimulator for the treatment of
neurological disorders
Abstract
A system for treating neurological conditions by low-frequency
time varying electrical stimulation includes an electrical device
for applying such low-frequency energy, in a range below
approximately 10 Hz, to the patient's brain tissue. An implantable
embodiment applies direct electrical stimulation to electrodes
implanted in or on the patient's brain, while a non-invasive
embodiment causes a magnetic field to induce electrical currents in
the patient's brain.
Inventors: |
Fischell, David R.; (Fair
Haven, NJ) ; Upton, Adrian R. M.; (Dundas,
CA) |
Correspondence
Address: |
NEUROPACE, INC.
255 SANTA ANA COURT
SUNNYVALE
CA
94085
US
|
Assignee: |
NeuroPace, Inc.
Sunnyvale
CA
|
Family ID: |
24618944 |
Appl. No.: |
10/245992 |
Filed: |
September 17, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10245992 |
Sep 17, 2002 |
|
|
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09652964 |
Aug 31, 2000 |
|
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Current U.S.
Class: |
600/13 ;
600/15 |
Current CPC
Class: |
A61N 1/36064 20130101;
A61N 2/008 20130101; A61N 2/006 20130101; A61N 1/36021 20130101;
A61N 2/02 20130101; A61N 1/36082 20130101; A61N 1/36025 20130101;
A61N 1/36071 20130101; A61N 1/32 20130101 |
Class at
Publication: |
600/13 ;
600/15 |
International
Class: |
A61N 001/00 |
Claims
What is claimed is:
1. A magnetic depolarizer system for the treatment of a
neurological disorder, the system comprising: a readily portable
magnetic depolarizer adapted for placement at a specific location
onto the head of a patient who is subjected to neurological events,
the magnetic depolarizer having a least one electromagnetic coil
that is capable of providing a time varying magnetic field pulsed
on and off at a rate between approximately 0.1 and 10 Hz, the
magnetic field having a peak intensity at some portion of the
patient's brain of at least 0.1 Tesla; electrical circuitry
connected to the magnetic depolarizer for providing an electrical
current through the at least one electromagnetic coil, the
electrical circuitry including at least one operating parameter
that is preset by a physician; and, a positioner for placing the
magnetic depolarizer system onto a specific region of the head of
the patient.
2. The magnetic depolarizer system of claim 1, wherein the
operating parameter comprises a frequency of application for the
time varying magnetic field.
3. The system of claim 1 wherein the magnetic depolarizer utilizes
two coils, in a race-track, figure-eight configuration.
4. The system of claim 1 wherein the electronic circuitry is
adapted to deliver at least one time varying magnetic pulse.
5. A magnetic depolarizer system for the treatment of a
neurological disorder, the system comprising: a readily portable
magnetic depolarizer adapted for placement at a specific location
onto the head of a patient who is subjected to neurological events,
the magnetic depolarizer having a least one electromagnetic coil
that is capable of providing a time varying magnetic field having a
stimulation frequency between approximately 0.1 and 10 Hz, the
magnetic field having a peak intensity at some portion of the
patient's brain of at least 0.1 Tesla; electrical circuitry
connected to the magnetic depolarizer for providing an electrical
current through the at least one electromagnetic coil, the
electrical circuitry including at least one operating parameter
that is preset by a physician; and, a positioner for placing the
magnetic depolarizer system onto a specific region of the head of
the patient.
6. The magnetic depolarizer system of claim 5, wherein the time
varying magnetic field has a carrier frequency of at least 100
Hz.
7. The magnetic depolarizer system of claim 5, wherein the time
varying magnetic field has a substantially sinusoidal waveform.
8. A method for treating a neurological disorder in a patient with
a readily portable magnetic depolarizer, the method comprising the
steps of: detecting a neurological event related to the
neurological disorder; activating the magnetic depolarizer; and
generating a time-varying magnetic field having a peak intensity at
some portion of the patient's cerebral cortex of at least
approximately 0.1 Tesla and a frequency of between approximately
0.1 Hz and 10 Hz.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is a division of U.S. Application Ser. No. 09/652,964,
filed on Aug. 31, 2000.
FIELD OF THE INVENTION
[0002] This invention is in the field of devices for the treatment
of neurological disorders in human subjects, particularly those
disorders that originate in the brain.
BACKGROUND OF THE INVENTION
[0003] The current state of the art in treating neurological
disorders such as epilepsy or Parkinson's disease involves either
drugs, destructive nigral lesions or the open-loop electrical
stimulation of neurological tissue. Drug therapy has been shown to
have significant short and long-term side effects and is often
ineffective. In U.S. Pat. No. 3,850,161, Liss describes a
continuous closed-loop feedback system which will always feedback
part of the brain EEG signal to separate electrodes so that if a
large EEG signal occurs it will be fed back in an attempt to cancel
out the original signal. This system does not take advantage of
recently developed digital signal processing and microcomputer
technology by which feedback signals can be activated only when a
neurological event occurs, nor does it provide a practical way to
recognize and intervene during early stages in the evolution of a
neurological event. In addition, the Liss device is not
programmable and it does not provide any capability to record EEG
signals. Examples of a "neurological event" are the occurrence of
an epileptic seizure, a tremor or the occurrence of a migraine aura
or migraine headache. A "neurological event" is defined herein as
either the precursor of an event such as an epileptic seizure, or
the event itself. This concept of detecting an electrical precursor
that is a first type of neurological event that occurs some time
before the "real" event (i.e. anomalous brain electrical activity
or a particular pattern of neural activity associated with clinical
symptoms) is an important aspect of the present invention. It has
been shown that both epileptic seizures and Parkinson's tremors
have precursors that occur before and can be used to predict the
onset of the clinical symptom. It is also very likely that other
neurological events such as migraine headaches and depression would
have anomalous electrical activity predictive of the onset of
clinical symptoms. Methods for prediction of epileptic seizures
have been published by Elger and Lehnertz (in Elger, C. E., and
Lehnertz, K., "Seizure prediction by non-linear time series
analysis of brain electrical activity," Eur. J. Neurosci. February
1998; 10(2):786-9, and Osorio, Frei and Wilkinson (in Osorio, I.,
et al., "Real-time automated detection and quantitative analysis of
seizures and short-term prediction of clinical onset," Epilepsia
June 1998 ; 39(6):615-27.
[0004] Maurer and Sorenson in U.S. Pat. No. 4,019,518 describe a
combined internal/external system for electrical stimulation of the
body with biphasic pulses but do not describe any means of
detecting neurological events. Fischell in U.S. Pat. No. 4,373,527
describes a programmable medication infusion system but does not
anticipate its use in response to a detected neurological
event.
[0005] More recently, a device has been approved for human use to
stimulate the vagus nerve in a continuous fashion with the
objective of decreasing the rate of epileptic seizures. Clinical
reports on such devices indicate only a modest degree of success in
that only 50% of the patients experience a greater than 20%
reduction in the rate of epileptic seizures. Another device that
has been recently introduced into clinical practice utilizes
intermittent or continuous stimulation of the thalamus for the
treatment of involuntary motion disorders such as Parkinson's
syndrome. Neither of these two open-loop devices described above is
highly effective for the treatment of a neurological disorder such
as epilepsy, and neither anticipates the use of decision making in
order to optimize a response to terminate the precursor of a
neurological event or the neurological event itself; nor does
either device allow for the recording of EEG signals. In addition,
both known devices use stimulation frequencies above 10 Hz, which
for the reasons set forth in detail below, are not optimal.
[0006] Fischell et al in U.S. Pat. No. 6,016,449, which is
incorporated herein by reference, teaches a fully implantable
neurostimulator capable of responsive treatment of neurological
disorders. However, Fischell does not discuss in detail the
advantageous use of low frequency stimulation as a means of
inhibiting epileptiform activity.
[0007] It is well known that slow wave potentials in the brain are
often inhibitory in nature yet all known stimulation attempts to
treat epilepsy in humans have used relatively high frequency
stimulation, in most cases greater than 20 Hz. These higher
frequencies, while effective for a brain mapping type procedure,
have significant potential to induce epileptogenic activity. In
fact, Hallett in "Transcranial magnetic stimulation and the human
brain," Nature, Vol. 406, 13 July 2000, states that while "rapid
repetitive transcranial magnetic stimulation (rTMS), at frequencies
of 5 Hz and higher, will transiently enhance motor excitability . .
. slow rTMS, at 1 Hz will transiently depress excitability."
SUMMARY OF THE INVENTION
[0008] There is good evidence that slow wave activity is inhibitory
in the central nervous system of man (Staton, R. D. et al., "The
electroencephalographic pattern during electroconvulsive therapy:
V. Observations on the origins of phase III delta energy and the
mechanism of action of ECT," Clin. Electroencephalogr. October
1988; 19(4):176-198 and animals (Buzsaki, G. et al., "Depth
profiles of hippocampal rhythmic slow activity (`theta rhythm`)
depend on behaviour," Electroencephalogr. Clin. Neurophysiol. July
1985; 61(1):77-88) including such stimulation applied to the
hippocampus (Leung, L. S. et al., "Theta-frequency resonance in
hippocampal CA1 neurons in vitro demonstrated by sinusoidal current
injection," J. Neurophysiol. March 1998; 79(3):1592-6). These slow
waves may be at theta frequencies (4 to 7 Hz--Buzsaki et al. 1985),
delta frequencies (1 to 3 Hz--Staton et al. 1988), or even at less
then 1 Hz (Contreras, D. et al., "Cellular basis of EEG slow
rhythms: a study of dynamic corticothalamic relationships," J.
Neurosci. January 1995; 15(1 Pt 2):604-22). Paatta et al. (in
"Control of chronic experimental focal epilepsy by feedback
caudatum stimulation," Epilepsia August 1983; 24(4):444-54)
describe successful ictal spike depression by 5 Hz stimulation of
the caudate nucleus (CN) in cat brains. The article also states
that stimulation of the thalamus, mesencephalic reticular formation
or hypothalamus was not effective. Finally, Hallett (in
"Transcranial magnetic stimulation and the human brain," Nature
2000; 406 (July 13): 147-150) discusses the inhibitory effects of
low frequency pulsing from a transcranial magnetic stimulator.
[0009] The present invention includes transcranial stimulation, or
direct brain stimulation from multiple electrodes, in either an
open or closed-loop system for the treatment of certain
neurological disorders such as epilepsy, migraine headaches and
Parkinson's disease. A purpose of the present invention is to
overcome the shortcomings of all known devices for the treatment of
such disorders. Specifically, the present invention utilizes slow
wave potentials (low frequency stimulation in a range of
approximately 1 to 10 Hz) to prevent or abort a neurological
event.
[0010] One embodiment of the present invention envisions a
multiplicity of brain electrodes placed either within the brain, on
the surface of the brain itself, or on the dura mater that
surrounds the brain. Some or all of these brain electrodes may be
used to directly detect an abnormal neurological event such as an
epileptic seizure, or they may be used to detect a pattern of
electrical activity that precedes or accompanies an abnormal
neurological event. A stimulation signal can also be applied to any
one, several, or all elements of such an electrode array. The
stimulation signals sent to each electrode may be identical or they
may be programmed to differ in amplitude, frequency, waveform,
phase and time duration. It is also envisioned that sensing
electrodes may be entirely separate from the electrodes used for
responsive stimulation.
[0011] It is also envisioned that appropriate selection (i.e.,
location) of electrode sites can be used to enhance the reliability
for detection and termination of a neurological event. Thus, the
present invention envisions enhancement of detection by the use of
the spatial domain as it applies to the positioning of detection
and treatment electrodes.
[0012] A specific capability of this system is to provide
electrical stimulation to a specific portion of the brain as the
means of stopping a neurological event. It is believed that the
earliest possible detection of a seizure and treatment of aberrant
electrical activity from an epileptic focus has the highest
probability of aborting the occurrence of a full seizure. It is
envisioned that either through specific placement of treatment
electrodes or by adjusting the phase of signals applied to an array
of electrodes, stimulation can be directed to the location(s)
within the brain that offer the highest probability of stopping the
seizure. Detection of an abnormal neurological event would allow
detection of specific but apparently normal patterns of electrical
activity, which are reliable producers of the abnormal event;
stimulation during the appearance of such patterns may prevent the
occurrence of the event.
[0013] A novel aspect of a preferred embodiment of this invention
is that the entire implantable portion of this system for treating
neurological disorders is implanted under the patient's scalp or
intracranially. Such placement will either have the device located
between the scalp and the cranium or the within a hole in the
cranium. Because of size constraints, the intracranial location is
the preferred embodiment.
[0014] The implantable portion of the system includes: (1)
electrodes that lie in close proximity to or actually within the
brain, (2) a control module that contains a battery and all the
electronics for sensing, recording and controlling brain activity,
(3) electrically conducting wires that connect the control module
to the electrodes, (4) a buzzer providing an acoustic signal or
electrical "tickle" indicating that a neurological event has been
detected, and (5) an input-output wire coil (or antenna) used for
communication of the implanted system with any and all external
equipment. The battery that provides power for the system and an
electronics module are both contained within a metal shell that
lies, in one embodiment, under the patient's scalp. The metal
shell, which contains the electronics module and the battery
collectively, forms the control module.
[0015] All electrodes connect by way of electrically conducting
wires to electrical terminals that are formed into the metal shell.
The electronics module is electrically joined to the brain
electrodes by way of the shell's electrical terminals, which are
electrically joined to the wires that connect to the brain
electrodes.
[0016] An important aspect of the preferred embodiment of this
device is the fact that the shell containing the electronics module
and the battery, i.e. the control module, is to be placed in the
cranium of the skull at a place where a significant volume of bone
is removed. By placing the entire system within the cranium, (as
opposed to having some wires extending into or through the
patient's neck to a control module in the chest) the probability of
wire breakage due to repeated wire bending is significantly
reduced. However, the present invention also envisions the
placement in the chest or abdomen of a control module if a large
battery or a large volume electronics module dictates such a large
size for the control module that it cannot be conveniently placed
within the cranium. Such a thoracic or abdominal placement of a
control module would typically require wires to be run through the
patient's neck.
[0017] The present invention also envisions the utilization of an
intracranial system for the treatment of certain diseases without
placing wires through the neck. Specifically, an alternative
embodiment of the invention envisions the use of electrodes in or
on the brain with an intracranial control module used in
conjunction with a remote sensor/actuator device implanted
elsewhere in the patient's body. For example, blood pressure could
be sensed with a threshold of, for example, 150 mm Hg, and if that
pressure is exceeded, a signal transmitted by electrical conduction
through the body from the remote sensor/actuator device could be
received at the control module, which would initiate brain
stimulation in such a way as to reduce the blood pressure.
Conversely, if the brain perceives pain and generates a
corresponding signal detectable by the intracranial control module,
a signal could be sent by electrical conduction through the body to
the remote sensor/actuator device, which would provide responsive
electrical stimulation to locally stimulate a nerve, thereby
reducing the perception of that pain. In still another embodiment,
if a precursor of an epileptic seizure is detected, the remote
sensor/actuator could be used to electrically stimulate one or both
vagus nerves so as to stop the epileptic seizure from occurring.
Such a remote device could be located in the trunk of the patient's
body. In an embodiment of the invention, a remote sensor/actuator
may be used to deliver instantaneous, intravenous, intraperitoneal,
subdural or intraventricular (of the brain) therapeutic chemicals,
including medication, neurotransmitters and ionic substances, alone
or in conjunction with electrical stimulation. Such a remote
sensor/actuator is disclosed in the above referenced U.S. Pat. No.
6,016,449 by Fischell et al.
[0018] It is also envisioned the ideal stimulation to prevent or
abort a neurological event has a low frequency (e.g., 1 to 8 Hz)
that would resemble slow wave inhibitory potentials and be
significantly less likely to induce epileptiform activity. In one
embodiment of the invention, the stimulation waveform is
substantially sinusoidal and has minimal higher-order harmonics,
and hence little energy above the fundamental frequency. In an
alternative embodiment, the low frequency stimulation comprises a
sequence of short duration biphasic pulses having a repetition rate
of less than about ten pulses per second (10 Hz). Such stimulation
could be applied to the caudate nucleus or other structures of the
brain, including the hippocampus. As patients suffering from
Parkinson's have an extremely low incidence of epilepsy and one
manifestation of Parkinson's is characterized by a 5 Hz electrical
oscillation that begins in the Thalamus, it is conceived that low
frequency stimulation of the Thalamus could, in fact, be inhibitory
to epileptiform activity. Such stimulation could be responsive to
the detection of a precursor to a clinical seizure or the
epileptiform activity from the seizure itself. Alternately,
periodic slow wave stimulation applied without detection could
prevent the brain from generating seizure activity. Although
epilepsy is currently believed to be the most applicable use of
such slow wave stimulation, it could also be successful for
migraines, pain, tremor, Parkinson's, depression or other
neurological disorders.
[0019] It is also envisioned that while the standard treatment
would have a constant amplitude for the duration of the low
frequency stimulation, it may be advantageous to have the amplitude
begin high and decrease over the duration, begin low and increase
over the duration, or vary according to any desired treatment plan.
The typical duration of low frequency stimulation that would be
used to stop a neurological event would be between 100 ms and 10
seconds.
[0020] Another embodiment of the present invention that would be
significantly less invasive involves the use of Transcranial
Magnetic Stimulation (TMS) from an external coil TMS stimulator.
Such a device could be incorporated into a bicycle type helmet and
could be used at the time a pre-event aura is sensed by the
patient. Alternately, such an external system could be used in a
repetitive or continuous mode for patients with serious disorders
who often wear protective helmets. A TMS device could be extremely
effective if it is pulsed on and off at frequencies below 10
Hz.
[0021] Thus it is an object of this invention to provide
appropriate slow wave stimulation of the human brain in response to
a detected neurological event in order to cause the cessation of
that neurological event. The pattern and frequency of stimulation
can be modified to provide optimal control of the unwanted
neurological event in each patient.
[0022] Another object of this invention is to use periodic slow
wave stimulation of the brain to treat neurological disorders.
[0023] Another object of this invention is to use continuous slow
wave stimulation of the brain to treat neurological disorders.
[0024] Still another object of this invention is to have a system
of electrodes connected by wires to a control module, the entire
system being placed under the scalp or intracranially, and being
substantially contained within an opening in the cranium.
[0025] Still another object of this system is to have essentially
no flexure of interconnecting wires so as to enhance system
reliability.
[0026] These and other objects and advantages of this invention
will become apparent to a person of ordinary skill in this art upon
careful reading of the detailed description of this invention
including the drawings as presented herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a top view of a human head showing the
configuration of an implantable system for the treatment of
neurological disorders, as it would be situated in the human
skull.
[0028] FIG. 2 is a block diagram of the implanted and external
portions of the system.
[0029] FIG. 3 is a cross section of an embodiment of the present
invention showing a magnetic depolarizer system within a helmet on
the head of a patient.
[0030] FIG. 4A is a longitudinal cross section of the magnetic
depolarizer.
[0031] FIG. 4B is a top view of the magnetic depolarizer.
[0032] FIG. 5 is a simplified circuit diagram of the main
components of a magnetic depolarizer system.
DETAILED DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 illustrates the configuration of an implantable
system 10 for the treatment of neurological disorders as it would
be situated under the scalp of a human head 9, the system including
a control module 20, electrodes 15A, 15B, 15C, 15N and 16 with
wires 17A, 17B, 17C, 17N and 18 connected through a connector 8 to
the control module 20. It is envisioned that the control module 20
is permanently implanted into the top of the patient's skull in a
location where the skull is fairly thick. It is also envisioned
that the control module 20 could be located in the trunk of the
patient's body like a heart pacemaker with the connecting wires
being run through the patient's neck, under the patient's skin or
otherwise. Each of the electrodes 15A, 15B, 15C, 15N and 16 would
be placed under the cranium and above the dura mater (i.e., placed
epidurally) or placed deep into the brain. The connecting wires
17A, 17B, 17C, 17N and 18 would be run from the control module 20
underneath the scalp and then be connected to the electrodes placed
beneath the patient's cranium. Although FIG. 1 shows only four
active electrodes 15A, 15B, 15C, 15N with connecting wires 17A,
17B, 17C, 17N, more than four active electrodes with connecting
wires may be used with the present invention. The electrode 16
(having the connecting wire 18) could be considered a common or
indifferent electrode.
[0034] Throughout the detailed description of the present
invention, the terminology "the electrodes 15A through 15N" is
meant to include all electrodes 15A, 15B, 15C, . . . to 15N,
inclusive, where N may be any integer greater than or equal to 1.
Similar terminology using the words "through" or "to" for other
groups of objects (i.e., wires 17A through 17N) will have a similar
inclusive meaning.
[0035] Throughout FIGS. 1 through 25, inclusive, lines connecting
boxes on block diagrams or on software flow charts will each be
labeled with an element number. Lines without arrows between boxes
or other elements shall indicate a single wire.
[0036] Lines with arrows connecting boxes or other elements are
used to represent any of the following:
[0037] 1. A physical connection, namely a wire or group of wires
(data bus) over which analog or digital signals may be sent.
[0038] 2. A data stream sent from one hardware element to another.
Data streams include messages, analog or digital signals, commands,
EEG information, and software downloads to change system operation
and parameters.
[0039] 3. A transfer of information between software modules. Such
transfers include software subroutine calls with and without the
passing of parameters, and the reading and writing of memory
locations.
[0040] In each case, the descriptive text herein will indicate each
specific use of a line with an arrow.
[0041] FIG. 2 is a block diagram of the implantable system 10 and
the external equipment 11. The wires 17A through 17N from the
electrodes 15A through 15N, and the wire 18 from the common
electrode 16, are shown connected to both an event detection
sub-system 30 and a stimulation sub-system 40. In one embodiment of
the invention, it is also envisioned to use the case of the control
module 20 of FIG. 1 as the common (or indifferent) electrode 16.
The wires 17A through 17N carry EEG signals 21A through 21N from
the electrodes 15A through 15N to the event detection sub-system
30. The electrodes 15A through 15N can be energized by the
stimulation sub-system 40 via the wires 17A through 17N to
electrically stimulate the patient's brain using the stimulation
signals 412A through 412N respectively. Although the electrodes 15A
through 15N and 16 shown here are connected to both the event
detection sub-system 30 and the stimulation sub-system 40, it
should be apparent that a separate set of electrodes and associated
wires could be used with each sub-system. Furthermore, it is
envisioned that any one or more of the electrodes 15A through 15N
could be electrically connected (i.e., shorted) to the electrode 16
or to each other. This would be accomplished by appropriate
switching circuitry in the stimulation sub-system 40.
[0042] The event detection sub-system 30 receives the EEG signals
21A through 21N (referenced to a system ground 19 connected to the
wire 18 from the common electrode 16) and processes them to
identify neurological events such as an epileptic seizure or its
precursor. A central processing system 50 with a central processor
51 and memory 55 acts to control and coordinate all functions of
the implantable system 10. A first interconnection 52 is used to
transmit programming parameters and instructions to the event
detection sub-system 30 from the central processing system 50. A
second interconnection 53 is used to transmit signals to the
central processing system 50 identifying the detection of a
neurological event by the event detection sub-system 30. The second
interconnection 53 is also used to transmit EEG and other related
data for storage in the memory 55.
[0043] When an event is detected by the event detection sub-system
30 (by processing such as that disclosed and described in U.S. Pat.
No. 6,016,449 to Fischell, et al., referenced above), the central
processor 51 can command the stimulation sub-system 40 via a third
interconnection 54 to transmit electrical signals to any one or
more of the electrodes 15A through 15N via the wires 17A through
17N. It is anticipated that, if appropriate, electrical signals
412A to 412N, inclusive, are transmitted to certain locations in or
near the brain, thereby aborting the normal progression of an
epileptic seizure. It may also be necessary for the stimulation
sub-system 40 to temporarily disable the event detection sub-system
30 via a fourth interconnection 29 when stimulation is imminent so
that the stimulation signals are not inadvertently interpreted as a
neurological event by the event detection sub-system 30.
[0044] The stimulation sub-system 40 may also be engaged to perform
continuous or periodic stimulation to the brain electrodes 15A
through 15N, inclusive. In one embodiment of the invention,
electrical stimulation from the stimulation sub-system 40 can
include any of a wide range of frequencies from approximately 2 Hz
to approximately 200 Hz. Details of a signal generator capable of
generating waveforms over such a frequency range are well known in
the art of electronics design. In connection with the invention, it
is, however, highly desirable to use stimulation at frequencies
below 10 Hz. In particular, 5 Hz stimulation has been shown to be
inhibitory to ictal spikes in cat brains, and it is believed to be
similarly effective in human patients. It is also known to be less
likely for low frequency stimulation to induce epileptiform
activity.
[0045] In one embodiment of the invention, the low-frequency
stimulation applied by an apparatus according to the invention
comprises a substantially sinusoidal waveform having little or no
energy in higher-frequency harmonics.
[0046] A power supply 90 provides power to each component of the
system 10. Power supplies for comparable implantable devices such
as heart pacemakers and heart defibrillators are well known in the
art of implantable electronic devices. Such a power supply
typically utilizes a primary (non-rechargeable) storage battery
with an associated d-c to d-c converter to obtain any voltages
required for the implantable system 10. However, it should be
understood that in an alternative embodiment of the invention, the
power supply could use a rechargeable battery that is charged by
means of a coil of wire in the control module 20 that receives
energy by magnetic induction from an external coil that is placed
outside the patient but in close proximity to the control module
20. The implanted coil of wire could also be located remotely from
control module 20 but joined to it by electrical wires. Such
technology is well known from the rechargeable cardiac pacemaker.
Furthermore, the same pair of coils of wire could be used to
provide power to the implanted system 10 when it is desired to read
out stored telemetry or reprogram some portion of the implanted
system 10.
[0047] The central processing system 50 is connected to a data
communication sub-system 60, thereby allowing data stored in the
memory 55 to be retrieved by the patient's physician via a wireless
communication link 72. An external data interface 70 can be
directly connected to the physician's workstation 80 via a
traditional serial data connection 74 (such as an RS-232
interface). Alternately, the serial connection may be made
trans-telephonically, via modems 85 and 750 and a phone line 75
from the patient's home to the physician's workstation 80. Software
in the computer section of the physician's workstation 80 allows
the physician to read out a history of events detected by the
implantable system 10, including EEG information before, during and
after each event, as well as specific information relating to the
detection of the event, such as the time evolving energy spectrum
of the patient's EEG. In a preferred embodiment of the invention,
the physician's workstation 80 also allows the physician to specify
or alter any programmable parameters of the implantable system
10.
[0048] As shown in FIGS. 1 and 2, a buzzer 95 connected to the
central processor 51 via a link 92 can be used to notify the
patient that a neurological event has occurred, the implanted
system 10 is about to deliver stimulation, or that the implanted
system 10 is not functioning properly. In alternative embodiments,
the buzzer could provide a mechanical vibration (typically an
acoustic signal) or an electrical stimulation "tickle," either of
which could be perceived by the patient. By placing the buzzer 95
near the ear and on the top of, below, or within a burr hole in the
cranium, an acoustic signal emitted by the buzzer 95 would be
transmitted via bone conduction and detectable by the patient's
ear. This sound by itself can be an automatic means for stopping an
epileptic seizure.
[0049] A real time clock 91 is used for timing and synchronizing
various portions of the implanted system 10 and also to enable the
system to provide the exact date and time corresponding to each
neurological event that is detected by the implantable system 10
and recorded in the memory 55. A fifth interconnection 96 is used
to send data from the central processor 51 to the real time clock
91 in order to set the correct date and time in the clock 91.
[0050] The various interconnections between sub-systems (e.g., the
illustrated interconnections 29, 52, 53, 54, 56, 57, 92, 93 and 96)
may be either analog or digital, single wire or multiple wires (a
"data bus").
[0051] In an embodiment of the invention, the operation of the
system 10 of FIG. 2 for detecting and treating a neurological event
such as an epileptic seizure would typically be as follows:
[0052] 1. The event detection sub-system 30 continuously processes
the EEG signals 21A through 21N carried by the wires 17A through
17N from the N electrodes 15A through 15N.
[0053] 2. When an event is detected, the event detection sub-system
30 notifies the central processor 51 via the second interconnection
53 that an event has occurred.
[0054] 3. The central processor 51 then triggers the stimulation
sub-system 40 via the third interconnection 54 to electrically
stimulate the patient's brain with low frequency electrical signals
in order to stop the neurological event, using any one, several or
all of the electrodes 15A through 15N.
[0055] 4. The stimulation sub-system 40 also sends a signal via the
fourth interconnection 29 to the event detection sub-system 30 to
disable event detection during stimulation to avoid an undesired
input into the event detection sub-system 30.
[0056] 5. The central processor system 50 will store EEG signals
and event related data received from the event detection sub-system
30 via the second interconnection 53 over a time from X minutes
before the event to Y minutes after the event for later analysis by
the patient's physician. The value of X and Y may be set from as
little as approximately 0.1 minutes to as long as approximately 30
minutes.
[0057] 6. The central processor 51 may generate a "buzz" to notify
the patient that an event has occurred by sending a signal via the
link 92 to the buzzer 95.
[0058] An alternative embodiment of the invention is shown in FIG.
3, which illustrates the head of a patient showing a cross section
of a non-invasive transcranial magnetic depolarizer system 100 as
it would be contained within a helmet 111 of the type used by
bicycle riders. The magnetic depolarizer system 100 consists of a
magnetic depolarizer coil assembly 112, a battery 114, electronic
circuitry 115, a recharging receptacle 116 and interconnecting
wires 117. The magnetic depolarizer system 100 is contained within
the helmet 111 by means of an elastic support 113 that passes
between a front support 111A and a rear support 111B. The purpose
of the elastic support 113 is to keep the magnetic depolarizer coil
112 in comparatively tight contact with the patient's head and at a
specific location relative to the patient's cerebral cortex.
[0059] FIG. 4A is a longitudinal cross section of the magnetic
depolarizer 112 of FIG. 3. The magnetic depolarizer coil assembly
112 consists of a first coil 121 placed into a figure-eight
configuration with a second coil 122. The two coils 121 and 122 are
electrically connected in series in such a way as to create north
magnetic poles 121A and 122A in essentially opposite directions
when electric current is flowing through the coils 121 and 122.
This orientation of coils 121 and 122 can produce a comparatively
strong magnetic field onto the cortex of the brain for a distance
of a few centimeters beneath the cranium. If the magnetic field
changes rapidly in time, it produces an electric current in the
brain that can cause excited neurons to be depolarized. Ideally,
slow TMS, at 1 to 5 Hz, will transiently depress excitability. In
an embodiment of the invention, the intensity of the magnetic field
at the surface of the brain should be between 0.1 and 10 Tesla. It
is therefore an object of the present invention to use a device
such as shown in FIG. 3 pulsed at a slow rate such as 1 or 2 Hz as
an external means for treating a neurological disorder; preferably,
this frequency is set and evaluated by the patient's physician.
Such a device could be worn all the time for chronic epileptics
where periodic slow stimulation would act to keep the focal region
in a depressed condition, thus preventing a hyper-excited state
associated with an epileptic seizure. For patients exhibiting an
aura, the helmet could be put on as needed.
[0060] It should also be understood that the patient could use one
or more elastic bands (without a helmet) to place the magnetic
depolarizer coil assembly 112 at an appropriate location onto his
or her head.
[0061] FIG. 4B is a top view of the magnetic depolarizer coil
assembly 112 showing as dotted lines the outline of the coils 121
and 122. In both FIGS. 3A and 3B, it is shown that the coils 121
and 122 could be encapsulated into a plastic housing 125.
Furthermore, FIG. 3A shows a magnetic core 123 in the coil 121 and
a separate magnetic core 124 in the coil 122. These cores 123 and
124 are not required for the device to perform its intended purpose
of generating a depolarizing electric current within the cerebral
cortex, but their presence facilitates the generation of a
high-intensity magnetic field in the brain at a lower level of
electric current in the coils 121 and 122. To be effective at the
high frequency of the magnetic pulses that are used to stimulate
the cortex, the cores 123 and 124 would typically be formed from
powdered iron or equivalent ferromagnetic material that has low
eddy current and hysteresis losses.
[0062] Although FIGS. 4A and 4B show a race-track, figure eight
type of design for the magnetic depolarizer coil assembly 112, it
should be understood that a simple cylindrical coil (and other
shaped coils as well) with or without a ferromagnetic core could be
used generate the desired time-varying magnetic field.
[0063] FIG. 5 is a simplified electrical diagram of the magnetic
depolarizer system 100. The rechargeable battery 114 can be
recharged through the receptacle 116 by receiving a plug from a
conventional AC adapter (not shown) that connects to a-c line
voltage (e.g., 115 volts) and delivers an appropriate d-c voltage
to recharge the rechargeable battery 114. When the patient is
experiencing an aura of a migraine headache or other symptoms of a
neurological disorder, he or she can throw the ON-OFF switch 129 to
the ON position. That would cause the d-c to d-c converter 130 to
activate and generate a high voltage for rapidly charging the
capacitor 126. When the control circuitry 128 senses that the
appropriate voltage has been reached, it moves the switch 127 from
position A to position B thus discharging the capacitor 126 through
the coils 121 and 122 of the magnetic depolarizer 112. As
previously described, the coils 121 and 122 could have air cores or
they could use magnetically permeable cores 123 and 124. The
control circuitry 128 can be used to set the repetition rate for
causing magnetic pulses to be delivered. For example, a pulse from
the capacitor might last for 70 microseconds and could be repeated
at the slow frequency rates between approximately 0.1 and 10 Hz. A
frequency of 1 Hz has been shown to be effective in depolarizing
brain neurons and may be ideal for some patients. However, other
patients might find other repetition rates to be more effective. It
is even possible that a single magnetic pulse having a time
duration between 10 and 1,000 microseconds could be used to stop an
aura, thereby preventing the occurrence of a neurological
event.
[0064] In an embodiment of the invention, the TMS administered
through a non-invasive magnetic depolarizer system according to the
invention comprises a low-frequency signal (between approximately
0.1 Hz and 10 Hz) modulated, via amplitude modulation or frequency
modulation, onto a carrier frequency on the order of 100 Hz. It
should be recognized that the carrier frequency given here is
considered representative of a beneficial and advantageous carrier
signal, and that various other carrier frequencies and modulation
schemes are possible. Various waveforms are also possible for both
the TMS waveform and the carrier waveform, including the
substantially sinusoidal wave described above. Circuits capable of
generating such stimulus signals are well known to practitioners
skilled in the art of electronic circuit design.
[0065] Although FIGS. 3 and 5 show a battery operated magnetic
depolarizer system 100, the system 100 could be operated by
plugging into a receptacle at (typically) 115 or 230 volts a-c.
Such a system might or might not use a battery as part of its
circuitry.
[0066] Additional objects and advantages of the present invention
will become apparent to those skilled in the art to which this
invention relates from the subsequent description of the preferred
embodiments and the appended claims, taken in conjunction with the
accompanying drawings.
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