U.S. patent application number 12/679051 was filed with the patent office on 2011-05-05 for electrode connection monitoring.
This patent application is currently assigned to Medotech A/S. Invention is credited to Faramarz Jadidi, Claus Steen.
Application Number | 20110105941 12/679051 |
Document ID | / |
Family ID | 40361439 |
Filed Date | 2011-05-05 |
United States Patent
Application |
20110105941 |
Kind Code |
A1 |
Jadidi; Faramarz ; et
al. |
May 5, 2011 |
ELECTRODE CONNECTION MONITORING
Abstract
The present invention relates to an apparatus and a method for
measuring muscular activity, in particular in relation to bruxism,
and providing an electrical stimulation in response to the measured
muscular activity through electrodes applied to the skin of an
individual, wherein the quality of the connectivity of the
electrodes to the skin is monitored and the electrical stimulation
signal is changed based on said quality measurement.
Inventors: |
Jadidi; Faramarz;
(Hasselager, DK) ; Steen; Claus; (Silkeborg,
DK) |
Assignee: |
Medotech A/S
|
Family ID: |
40361439 |
Appl. No.: |
12/679051 |
Filed: |
September 22, 2008 |
PCT Filed: |
September 22, 2008 |
PCT NO: |
PCT/DK08/50231 |
371 Date: |
January 13, 2011 |
Current U.S.
Class: |
600/546 |
Current CPC
Class: |
A61B 5/276 20210101;
A61B 5/486 20130101; A61B 5/6843 20130101; A61B 5/4557 20130101;
A61N 1/36034 20170801; A61B 5/1104 20130101; A61B 5/389 20210101;
A61N 1/36031 20170801; A61B 5/7257 20130101 |
Class at
Publication: |
600/546 |
International
Class: |
A61B 5/0488 20060101
A61B005/0488 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 21, 2007 |
GB |
0718486.4 |
Sep 21, 2007 |
GB |
0718487.2 |
Claims
1-35. (canceled)
36. Apparatus comprising: an electrode assembly comprising three
electrodes: a first, a second and a reference electrode, mounted on
a common substrate in a fixed spatial relationship one to another
wherein said reference electrode lies approximately equidistant
from said first and second electrodes, said electrode assembly
adapted for being applied to the skin of an individual, wherein the
apparatus is operative to receive and monitor electrical signals
and provide electrical stimulation to said individual, said
apparatus further comprising: inputs for receiving signals from
said electrodes, means for measuring EMG signals from said
electrode(s) when the electrodes are applied to the skin, a source
of a monitoring signal having a frequency and outputs for use in
applying said monitoring signal alternately to said first and
second electrodes, means for determining the amplitude of the
frequency of the monitoring signal at the input of said reference
electrode, means for providing an electrical stimulation feedback
signal to the reference electrode upon the detection of EMG signals
indicative of a muscular activity relating to bruxism of the
individual, wherein said apparatus is configured so that said
monitoring signal is applied at a voltage sufficient to produce a
preset current between the first electrode and the reference
electrode and between the second electrode and the reference
electrode, wherein the amplitude of the frequency of the monitoring
signal at said reference electrode is measured to determine the
quality of the connection via the skin between the first electrode
and the reference electrode and the quality of the connection via
the skin between the second electrode and the reference electrode,
and wherein the feedback signal is modulated if the quality of the
electrical connection between the electrodes is changed.
37. Apparatus as claimed in claim 36, comprising a Fourier
transform analyser for extracting frequency content information
from said received signals.
38. Apparatus as claimed in claim 36, further comprising means for
measuring the amplitude within the received signals of at least one
selected frequency other than that of said monitoring signal.
39. Apparatus as claimed in claim 37, wherein said apparatus is for
measuring EMG signals from said electrodes when the electrodes are
applied to the skin and the amplitude of the said frequency of the
monitoring signal in signals received at said inputs as determined
by said Fourier transform analyser is measured for monitoring the
quality of the electrical connection between the electrodes and the
skin.
40. Apparatus as claimed in claim 36, wherein said EMG signals
indicative of the muscular activity are identified by measuring
therein the amplitude of one or more selected frequencies different
from the frequency of the monitoring signal.
41. Apparatus as claimed in claim 36, wherein the feedback signal
is reduced when the quality of the electrical connection is
reduced.
42. Apparatus according to claim 36, wherein the feedback signal is
reduced if the amplitude of the said frequency of the monitoring
signal in signals received at said inputs is not below a preset
threshold level or wherein the intensity of the feedback signal is
reduced if the amplitude of the said frequency of the monitoring
signal in signals received at said inputs is not below a preset
threshold level.
43. Apparatus as claimed in claim 42, wherein the feedback signal
is reduced by half or blocked.
44. A method for monitoring activity of the temporal muscle and/or
the masseter muscle, in particular activity due to teeth and/or jaw
clenching, said method comprising the steps of: providing an
apparatus as defined in claim 1 comprising electrode(s), measuring
EMG signals from said electrode(s) when the electrodes are applied
to the skin, applying a monitoring signal having a frequency to
said at least first electrode, determining the received signal of
said frequency of the monitoring signal in signals received, for
monitoring the quality of the electrical connection between the
electrodes and the skin, providing an electrical stimulation
feedback signal upon the detection of EMG signals indicative of a
muscular activity of the individual, wherein the feedback signal is
modulated if the quality of the electrical connection between the
electrodes is changed.
45. The method as claimed in claim 44, wherein the receiving signal
is determined by determining the amplitude of the said frequency of
the monitoring signal in signals received.
46. The method as claimed in claim 44, comprising extracting
frequency content information from said received signals and
performing a Fourier transform analysis, such as an FFT
analysis.
47. The method as claimed in claim 44, comprising for receiving
signals from said first electrode, from a second electrode and from
said reference electrode.
48. The method as claimed in claim 47, wherein the respective
electrodes are connected.
49. The method as claimed in claim 44, wherein said electrodes are
provided in an electrode assembly in which said electrode assembly
comprises three electrodes mounted on a common substrate in a fixed
spatial relationship one to another.
50. The method as claimed in claim 44, wherein said reference
electrode lies approximately equidistant from said first and second
electrodes.
51. The method as claimed claim 44, further comprising the step of
measuring the amplitude within the received signals of at least one
selected frequency other than that of said monitoring signal.
52. The method as claimed in claim 44, wherein said activity is an
episode of bruxism.
53. The method as claimed in claim 44, wherein said EMG signals
indicative of the muscular activity are identified by measuring
therein the amplitude of one or more selected frequencies different
from the frequency of the monitoring signal.
54. The method as claimed in claim 44, wherein the feedback signal
is reduced, when the quality of the electrical connection is
reduced.
55. The method according to claim 44, wherein the feedback signal
is reduced if the amplitude of the said frequency of the monitoring
signal in signals received is not below a preset threshold level or
wherein the intensity of the feedback signal is reduced if the
amplitude of the said frequency of the monitoring signal in signals
received is not below a preset threshold level.
56. The method as claimed in claim 44, wherein the feedback signal
is reduced by half or blocked.
57. The method as claimed in claim 44, wherein said monitoring
signal is applied at a voltage sufficient to produce a preset
current between the first electrode and the reference electrode and
between the second electrode and the reference electrode.
Description
FIELD OF INVENTION
[0001] The present invention relates to an apparatus and a method
for use in analysing EMG signals. The apparatus provides for
monitoring the quality of the connection of EMG electrodes to the
source of said signals, which is normally the skin.
BACKGROUND OF INVENTION
[0002] In conducting the measurement of EMG signals, electrodes are
placed or adhered onto the skin, usually with a layer of
electrically conducting gel between the skin surface and the
electrode proper. The quality of the signals received will depend
on the quality of the connection made between the skin and the
electrode, and this may not be easy for the user to ascertain. If
the connection is poor, the sensing of particular signals may fail
and actions that should be triggered in response to particular
conditions may not take place. In Functional Electrical Stimulation
systems, electric currents are impressed on the skin by voltage
applied via skin electrodes either to produce a muscular reaction
or to provide a sensory input. If the connection between the
electrode and the skin is poor, this can lead to excessive voltage
being applied or can lead to a failure to produce the desired
effect.
[0003] For instance, in WO2004/087258, episodes of bruxism are
detected by monitoring EMG signals received from electrodes on the
skin of a user and when such an episode is detected, an mild
electric shock is applied via the electrodes as a biofeedback
signal. In order that the apparatus can function correctly to
detect the bruxism episodes and also to apply the biofeedback
signal safely, a good connection between the skin and the
electrodes is required. It is described that the connection can be
checked by applying a voltage between a pair of the electrodes to
be tested, so as to produce a predetermined current, and measuring
the voltage required, and further that the user is informed, in
case of reduced connection, to adjust the apparatus, such as the
strap pressing the electrodes to the skin.
[0004] All patent and non-patent references cited in the
application, or in the present application, are also hereby
incorporated by reference in their entirety.
SUMMARY OF INVENTION
[0005] The present invention relates to an apparatus and a method
for measuring muscular activity, in particular in relation to
bruxism, and providing an electrical stimulation in response to the
measured muscular activity through electrodes applied to the skin
of an individual, wherein the quality of the connectivity of the
electrodes to the skin is monitored and the electrical stimulation
signal is changed based on said quality measurement.
[0006] Accordingly, in a first aspect the invention relates to an
apparatus comprising electrodes adapted for being applied to the
skin of an individual, wherein the apparatus is adapted for
receiving and monitoring electrical signals and comprises
respective inputs for receiving signals from at least a first
electrode of said electrodes and a reference electrode, and for
providing electrical stimulation to said individual, said apparatus
comprising [0007] means for measuring EMG signals from said
electrode(s) when the electrodes are applied to the skin, [0008] a
source of a monitoring signal having a frequency, an output for use
in applying said monitoring signal to said at least first
electrode, [0009] means for determining the received signal of said
frequency of the monitoring signal in signals received at said
inputs, [0010] means for providing an electrical stimulation
feedback signal upon the detection of EMG signals indicative of a
muscular activity of the individual, [0011] wherein the received
signal of said frequency of the monitoring signal in signals
received at said inputs is measured for monitoring the quality of
the electrical connection between the electrodes and the skin, and
the feedback signal is modulated if the quality of the electrical
connection between the electrodes is changed.
[0012] Furthermore, the present invention provides a method for
monitoring the electrode connection, wherein the incoming signals
relating to the monitoring signals are analysed by a Fourier
transform analyser. Accordingly, in a second aspect the invention
relates to an apparatus for receiving and monitoring electrical
signals comprising respective inputs for receiving signals from at
least a first electrode and a reference electrode, a Fourier
transform analyser for extracting frequency content information
from said signals, a source of a monitoring signal having a
frequency, an output for use in applying said monitoring signal to
a said electrode, and means for determining the amplitude of the
said frequency of the monitoring signal in signals received at said
inputs as determined by said Fourier transform analyser.
[0013] In yet another aspect the invention relates to a method for
ameliorating and/or treating bruxism by applying electrodes as
described above to the skin above a facial muscle of said
individual, preferably the masseter muscle or the temporalis
muscle, applying a stimulating signal, should a bruxism event
happen, and monitoring the connection between the electrodes and
the skin. Accordingly, the invention relates to A method for
monitoring activity of the temporal muscle and/or the masseter
muscle, in particular activity due to teeth and/or jaw clenching,
said method comprising the steps of: [0014] measuring EMG signals
from said electrode(s) when the electrodes are applied to the skin,
[0015] applying a monitoring signal having a frequency to said at
least first electrode, [0016] determining the received signal of
said frequency of the monitoring signal in signals received, for
monitoring the quality of the electrical connection between the
electrodes and the skin [0017] providing an electrical stimulation
feedback signal upon the detection of EMG signals indicative of a
muscular activity of the individual, [0018] wherein the feedback
signal is modulated if the quality of the electrical connection
between the electrodes is changed.
[0019] Furthermore, the invention relates to a method for
monitoring electrode connections, by receiving and monitoring
electrical signals from at least a first electrode and a reference
electrode, extracting frequency content information from said
signals and performing a Fourier transform analysis, applying said
monitoring signal to a said electrode, and determining the
amplitude of the said frequency of the monitoring signal in signals
received as determined by said Fourier transform analyser.
DESCRIPTION OF DRAWINGS
[0020] FIG. 1 shows a block circuit diagram for a bruxism
monitoring apparatus of the kind described in WO2004/087258 but
modified to incorporate electrode connection monitoring according
to the present invention;
[0021] FIG. 2 is a block circuit diagram showing the components of
the apparatus of FIG. 1 that are relevant to the electrode
connection monitoring.
DETAILED DESCRIPTION OF THE INVENTION
[0022] As described above the apparatus according to the invention
has electrodes adapted for being applied to the skin of an
individual for measuring EMG as a measure for muscular activity, in
particular in relation to bruxism, and providing an electrical
stimulation in response to the measured muscular activity through
the electrodes. The apparatus is in particular useful for measuring
muscular activity relating to bruxism during night when the
individual is at sleep. Accordingly, the electrodes are applied to
the skin before the individual goes to bed and must stay on the
skin during the sleep until next morning in order to be effective.
The connection of the electrodes may be of good quality at the
start of the sleep, however due to changes in for example
temperature, pressure and general movements of the individual the
quality of the connection may be reduced during the sleep. Thus,
the present invention provides an apparatus wherein the quality of
the connection may be monitored during use of the apparatus, and
furthermore, that the electrical feedback stimulation signal may be
changed due to changes in the connection, in order to reduce harm
to the individual and maintain efficiency of the apparatus, at
least to some degree.
[0023] It will be appreciated that the electrodes may each comprise
a solid conductive electrode member provided with a respective
patch of conductive gel in an assembly, in which case it will be
the area of the gel that defines the contact area of the electrode
rather than the size of the electrode member. However, even when a
gel is used the connection between electrode and skin may vary
depending on a variety of factors, such as described above. The
area of an electrode member in contact with such a gel patch may be
approximately from 5% to 100% of the electrode contact area (i.e.
the gel patch area), in some cases 25% to 75%, e.g. about 50%.
[0024] The electrode contact areas may extend along or on a said
line a distance of from 1 to 10 mm from one side to an opposite
side of the electrode contact area and may extend transversely of a
said line by a distance of from 1 to 10 mm from one side to an
opposite side of the electrode contact area, the maximum distance
along said line from an edge of a first said electrode contact area
to an opposite edge of the furthest away of the other two electrode
contact areas being not more than 60 mm, more preferably 50 mm.
Preferably, the contact areas of the electrodes may extend along or
on said line a distance of from 3 to 7 mm from one side to an
opposite side of the electrode contact area. Similarly, the contact
areas of the electrodes may extend transversely of said line by a
distance of from 3 to 7 mm from one side to an opposite side of the
electrode contact area.
[0025] Thus, for instance the electrode contact areas may be
circular and of diameter from 2-20 mm, more preferably from 5-15
mm, e.g. about 10 mm, and the electrode members may also be
circular having a diameter of from 1-10 mm, more preferably from 3
to 7 mm, e.g. about 5 mm. The electrode contact areas and the
electrode members may be of other shapes having equivalent areas to
those described above.
[0026] Preferably, the apparatus comprises respective inputs for
receiving signals from said first electrode, from a second
electrode and from said reference electrode. Preferably, there are
inputs for just the three electrodes, although more may be
provided. Preferably, there are respective outputs for applying
said monitoring signal to each of the first electrode and the
second electrode.
[0027] The apparatus preferably further comprises respective
electrodes connected to said inputs and to said output(s).
[0028] Preferably, the apparatus further comprises circuit means
adapted to provide a preset monitoring signal current between said
first electrode and said reference electrode, and optionally also
circuit means adapted to provide a preset monitoring signal current
between said second electrode and said reference electrode. The
means for determining the received signal of said frequency, may be
provided to determine and optionally to record the voltage
amplitude of said monitoring signal required to achieve said preset
current level between said electrode pair(s). Thus, the quality of
the connection between the electrodes through a material to which
they are connected may be determined.
[0029] Said electrodes are preferably provided in an electrode
assembly in which said electrode assembly comprises two or more
preferably three electrodes mounted on a common substrate in a
fixed spatial relationship one to another. Said electrode assembly
is preferably adapted to be applied to the skin above the masseter
or temporalis muscles, ie. of a shape adapted to follow the facial
contours most generally met at the various individuals to be
treated.
[0030] Preferably, where first, second and reference electrodes are
provided, said reference electrode lies approximately equidistant
from said first and second electrodes.
[0031] The apparatus may comprise means for measuring the amplitude
within the received signals of at least one selected frequency
other than that of said monitoring signal.
[0032] In a preferred aspect of the practise of the invention, said
apparatus is for measuring EMG signals from said electrodes when
the electrodes are applied to the skin and the amplitude of the
said frequency of the monitoring signal in signals received at said
inputs as determined by said Fourier transform analyser is measured
for monitoring the quality of the electrical connection between the
electrodes and the skin.
[0033] Preferably, the apparatus is for functional electrical
stimulation (FES). In some FES devices, electrical stimulating
pulses are delivered via skin mounted electrodes to activate muscle
functions. In such devices it will be desirable to be able to
monitor the connection to the skin of the electrodes by the use of
apparatus according to the invention. However, apparatus according
to the invention preferably also comprises means for the detection
of EMG signals and means for providing a feedback signal upon the
detection of EMG signals indicative of a muscular activity.
[0034] In particular, said activity may be an episode of
bruxism.
[0035] In order that the stimulation signal has the desired effect
on bruxism behaviour and yet does not wake the user from sleep, or
is adjustable to achieve these ends, a match is needed between the
form of the signal and the form of the electrode assembly. For use
with the electrode assembly conformations described herein, it is
preferred that said electrical stimulation signal is a biphasic
signal which is initiated at a voltage applied to the electrode
assembly of not more than 10 volts peak to peak and is raised to a
maximum peak to peak voltage at a rate of not more than 500 V/sec,
said signal having a duration of not more than 2 sec, a said
maximum voltage of not more than 100 volts peak to peak.
[0036] Preferably, said biphasic signal has a pulse width of from
50 .mu.sec to 10 msec, more preferably from 50 to 500 .mu.sec, more
preferably from 100 to 300 .mu.sec, for instance about 150
.mu.sec.
[0037] The signal is preferably initiated at a voltage applied to
the electrode assembly of not more than 5 volts peak to peak. The
signal preferably increases in intensity from its initial value at
a rate of not more than 350 V/sec, more preferably not more than
250 V/sec, for instance between 100 and 250 V/sec, e.g. about
200V/sec.
[0038] The duty cycle of the signal may be from 1 to 99%, but is
preferably in the range of from 30 to 70%, suitably about 50%.
[0039] The frequencies of muscle activity are normally in the range
of from 0 to about 350 Hz, whereas the frequencies of bruxism
related muscle activity is normally found in the range of from
250-350 Hz, more specifically from 268-332 Hz. The frequency of the
monitoring signal is preferably different from the frequencies of
muscle activity, and more preferably the frequency of the
monitoring signal is higher than the frequencies of muscle
activity. Accordingly, the frequency of the monitoring signal is
preferably above 350 Hz, more preferably above 400 Hz, more
preferably above 450 Hz, more preferably above 500 Hz, and even
more preferably about 600 Hz.
[0040] Preferably, said EMG signals indicative of the muscular
activity are identified by measuring therein the amplitude of one
or more selected frequencies different from the frequency of the
monitoring signal. The measured frequency or frequencies may be
selected for maximal differentiation between bruxism activity and
possibly confounding muscular activities such as changes in facial
expression, e.g. grimacing, and they may be selected to best suit
detection of bruxism in an individual user. Apparatus to which the
invention may be applied is described in WO 2004/087258.
[0041] If the quality of the connection between the electrode(s)
and the skin is reduced, it is preferred that the electrical
stimulation signal is changed based on said quality measurement.
For example, if the determination of the received signal of said
frequency of the monitoring signal implies a poor connection
between then it is preferred that the feedback stimulation signal
is reduced, such as wherein the intensity of the feedback
stimulation signal is reduced. In a preferred embodiment the
feedback stimulation signal is reduced by half, to avoid burning or
skin irritation due to too great a current being passed from one
electrode to a better connected electrode. In yet another
embodiment the feedback stimulation signal may be blocked.
[0042] Accordingly, in one embodiment an interlock may be provided
such that the means for providing a feedback signal upon the
detection of EMG signals indicative of a muscular activity is
prevented from so doing if the amplitude of the said frequency of
the monitoring signal in signals received at said inputs is not
indicative of a sufficiently good connection, e.g. is not below a
preset threshold level of voltage sufficient to provide a set level
of current, or wherein the intensity of the feedback signal is
reduced if there is not a sufficiently good connection, e.g. if the
amplitude of the said frequency of the monitoring signal in signals
received at said inputs is not below a preset threshold level of
voltage sufficient to provide a set level of current, e.g. if the
amplitude of the said frequency of the monitoring signal in signals
received at said inputs is not below a preset threshold level of
voltage sufficient to provide a set level of current.
[0043] Thus, where electrodes are placed on the skin and a feedback
stimulation signal is applied through them, the apparatus according
to the invention can avoid the feedback signal being provided if
the connection to the skin is not sufficiently good, and thus the
risk of skin irritation or burning may be avoided.
[0044] Preferably, the apparatus comprises a said first electrode,
a said second electrode and a said reference electrode, said
monitoring signal is applied to said first electrode and to said
second electrode and the amplitude of the frequency of the
monitoring signal at said reference electrode is measured to
determine the quality of the connection via the skin between the
first electrode and the reference electrode and the quality of the
connection via the skin between the second electrode and the
reference electrode.
[0045] Suitably, said monitoring signal is applied at a voltage
sufficient to produce a preset current between the first electrode
and the reference electrode and between the second electrode and
the reference electrode.
[0046] An advantage of the use of a monitoring signal of known
frequency that is detected via analysis of received signals is that
the monitoring may be carried out continuously, whilst EMG signals
are simultaneously detected and evaluated.
[0047] An index indicative of the quality of the electrode
connections as monitored over a period of time may be recorded,
suitably providing a single FIGURE which indicates to a user how
good over the use period the connection has been. The index figure
may for instance be generated by producing a numerical output
indicative of the quality of connection at periodic intervals and
averaging the values of said numerical output values over time.
[0048] In one aspect, the invention provides a novel approach to
monitoring electrode connections, such as electrode connections to
the skin of an individual. Accordingly, the present invention
provides apparatus for receiving and monitoring electrical signals
comprising respective inputs for receiving signals from at least a
first electrode and a reference electrode, a Fourier transform
analyser for extracting frequency content information from said
signals, a source of a monitoring signal having a frequency, an
output for use in applying said monitoring signal to a said
electrode, and means for determining the amplitude of the said
frequency of the monitoring signal in signals received at said
inputs as determined by said Fourier transform analyser.
[0049] The Fourier transform analyser is preferably a DFT analyser,
such as an FFT analyser. This can provide a power spectrum of the
received signals in which the amplitude of the signal at the
frequency of the monitoring signal can be determined.
[0050] In yet another aspect the invention relates to a method for
ameliorating and/or treating undesired muscular activity, in
particularly bruxism, by applying electrodes as described above to
the skin above a facial muscle of said individual, preferably the
masseter muscle or the temporalis muscle, applying a stimulating
signal, should a bruxism event happen, and monitoring the
connection between the electrodes and the skin. Accordingly, in a
further aspect the invention relates to a method for monitoring
activity of the temporal muscle and/or the masseter muscle, in
particular activity due to teeth and/or jaw clenching, said method
comprising the steps of: [0051] measuring EMG signals from said
electrode(s) when the electrodes are applied to the skin, [0052]
applying a monitoring signal having a frequency to said at least
first electrode, [0053] determining the received signal of said
frequency of the monitoring signal in signals received, for
monitoring the quality of the electrical connection between the
electrodes and the skin [0054] providing an electrical stimulation
feedback signal upon the detection of EMG signals indicative of a
muscular activity of the individual, wherein the feedback signal is
modulated if the quality of the electrical connection between the
electrodes is changed. Embodiments of this aspect is described
above in relation to the apparatus.
[0055] Furthermore, the present invention provides a method for
monitoring the electrode connection, wherein the incoming signals
relating to the monitoring signals are analysed by a Fourier
transform analyser. Accordingly, in another aspect, the invention
relates to a method for monitoring electrode connections, by
receiving and monitoring electrical signals from at least a first
electrode and a reference electrode, extracting frequency content
information from said signals and performing a Fourier transform
analysis, applying said monitoring signal to a said electrode, and
determining the amplitude of the said frequency of the monitoring
signal in signals received as determined by said Fourier transform
analyser. Embodiments of this aspect is described above in relation
to the apparatus.
[0056] The invention will be further described and illustrated by
reference to the accompanying drawings in which:
DETAILED DESCRIPTION OF THE DRAWINGS
[0057] The circuitry shown in FIGS. 1 and 2 is that of apparatus
for monitoring bruxism which is generally of the kind described in
detail in WO 2004/087258. The apparatus has an electrode assembly
comprising a first electrode 10, a second electrode 14 and a
reference electrode 12 disposed between the first and second
electrodes. The three electrodes are applied to the skin of a user
above either the temporal muscle (musculus temporalis) or the
masseter muscle (musculus masseter). EMG signals received from the
electrodes 10 and 14 are fed via an analog switch, switching
between sending and receiving functions as discussed below, to an
Instrumentation amplifier and then to a notch filter for removing
ambient 50/60 Hz noise. After processing by a digital amplifier the
signals are low pass filtered with a cut off nominally at 500 Hz
which allows a significant amount of the frequency content of the
monitoring signal at 610 Hz to pass. The resulting filtered signals
are subjected to FFT analysis in a micro-processor to analyse their
frequency content. The micro-processor further controls the
switching of that analogue switch between receiving and sending
states.
[0058] If there is found to be present a sufficient amplitude at
one or more preset frequencies or within one or more preset
frequency bands in the received EMG signals, it is considered that
an episode of bruxism is occurring and an instruction is sent to
the unit marked `stimulator` to generate a stimulation signal,
which is applied to the reference electrode. This gives the user a
mild electric shock which is designed to be insufficient to wake
them if they are sleeping. Current passes from the reference
electrode to each of the first and second electrodes.
[0059] The micro-processor also outputs trigger signals to a first
output 16 and to a second output 18 which connect respectively to
first and second monitor signal generators DAC0 and DAC1 which
convert the digital trigger signals to a 610 Hz sine wave
monitoring signal. The monitoring signals are thereby applied
alternately to the first and second electrodes via a filter to
dampen the signal and to exclude a DC component (FIG. 2) at a
voltage sufficient to achieve a preset current value. The voltage
is therefore dependent on the resistance between the relevant
electrodes (electrode 10 to reference 12 in the case of DAC0 and
electrode 14 to reference 12 in the case of DAC1). As shown in FIG.
2, the monitor signals are picked up from the reference electrode
and are fed to an analogue to digital converter and are analysed in
the micro-processor as part of the FFT analysis of the EMG signals
received from the first and second electrodes.
[0060] Sufficient of the applied 610 Hz signal passes the filters
to be picked up in the EMG signals.
[0061] If the amplitude of the monitoring signal voltage applied to
one (but not the other) of electrodes 10 and 14 to achieve the
preset current is too high, implying a poor connection between the
electrodes, the stimulation signal intensity is reduced, suitably
by half, to avoid burning or skin irritation due to too great a
current being passed from the reference electrode 12 to just the
better connected one of the first and second electrodes 10, 14. If
the amplitude of the monitoring signal is too high as received from
both of the electrodes 10, 14, then the giving of the stimulation
signal is blocked. This could be due to a poor connection either at
both of electrodes 10 and 14, or just at the reference electrode.
It can happen that one or both of the first and second electrodes
becomes short circuited to the reference electrode, for instance if
conductive gel becomes smeared over the skin between them. One will
then detect too low an amplitude of the 610 Hz monitoring
signal.
[0062] A log is written in the apparatus for the purposes of
informing the user that one or both electrodes was not adequately
connected during the session.
[0063] In a set-up phase of the use of the apparatus, the
monitoring signals are used as a basis for confirming to the user
(or not as appropriate) that an initial good connection of the
electrode assembly has been made.
[0064] In this specification, unless expressly otherwise indicated,
the word `or` is used in the sense of an operator that returns a
true value when either or both of the stated conditions is met, as
opposed to the operator `exclusive or` which requires that only one
of the conditions is met. The word `comprising` is used in the
sense of `including` rather than in to mean `consisting of`.
* * * * *