United States Patent |
5,922,016
|
Wagner
|
July 13, 1999
|
Apparatus for electric stimulation of auditory nerves of a human being
Abstract
Apparatus for electric stimulation and diagnostics of auditory nerves of a
human being, e.g. for determination of sensation level (SL), most
conformable level (MCL) and uncomfortable level (UCL) audibility curves,
includes a stimulator detachably secured to a human being for sending a
signal into a human ear, and an electrode placed within the human ear and
electrically connected to the stimulator by an electric conductor for
conducting the signals from the stimulator into the ear. A control unit is
operatively connected to the stimulator for instructing the stimulator as
to characteristics of the generated signals being transmitted to the ear.
Inventors:
|
Wagner; Hermann (Berlin, DE)
|
Assignee:
|
Hochmair; Ingeborg (Axams/Tirol, AT);
Hochmair; Erwin (Axams/Tirol, AT)
|
Appl. No.:
|
590567 |
Filed:
|
January 26, 1996 |
Current U.S. Class: |
607/137; 128/898; 600/559 |
Intern'l Class: |
A61F 002/18 |
Field of Search: |
607/55,56,136,137
128/898
381/312,60
600/559
|
References Cited
U.S. Patent Documents
3799146 | Mar., 1974 | John et al. | 128/2.
|
4535785 | Aug., 1985 | Van Den Honert et al. | 128/746.
|
4577641 | Mar., 1986 | Hochmair et al. | 128/746.
|
4858612 | Aug., 1989 | Stocklin | 607/136.
|
5119826 | Jun., 1992 | Baart De La Faille | 128/746.
|
5291785 | Mar., 1994 | Downs | 73/585.
|
5395301 | Mar., 1995 | Russek | 601/41.
|
Primary Examiner: Lavinder; Jack W.
Assistant Examiner: Ruddy; David M
Attorney, Agent or Firm: Feiereisen; Henry M.
Claims
What is claimed as new and desired to be protected by Letters Patent is set
forth in the appended claims:
1. Method for testing a response of auditory nerves of a human being to an
electric stimulation signal, comprising:
placing an electrode within the human ear of a hearing impaired human
being, said electrode contacting areas in the human ear susceptive to
stimulation by said electric stimulation signal;
applying to said electrode electric signals having a plurality of
frequencies and a plurality of intensities for eliciting a sensory
response from said human being as a function of said frequencies and
intensities for deriving characteristic features of audibility curves for
said human being;
comparing said sensory response from said human being to audibility curves
derived at approximately identical frequencies of healthy human beings;
and
predicting from said comparison the likelihood of success of a permanent
cochlear implant for said hearing impaired human being.
2. The method of claim 1, wherein said frequencies are in a range between
about 60 Hz and 2 kHz.
3. The method of claim 1, wherein said electrode is placed in the auditory
meatus of the human ear.
4. The method of claim 1, wherein said audibility curves comprise SL-, MCL-
and UCL-audibility curves of the auditory meatus of said human being.
5. The method of claim 1, wherein placing the electrode further comprises
embedding the electrode in an electrolyte body and sealing the auditory
meatus from the outside with a plastic body.
6. The method of claim 1, wherein said electrical signals are transmitted
to said electrode by a detachable stimulator.
7. The method of claim 1, wherein eliciting a response further comprises
optically signaling during transmission of said stimulation signals.
8. The method of claim 7, wherein said optical signaling is provided by a
toy suitable for infants.
9. The method of claim 8, wherein said optical signaling is provided by a
toy truck.
Description
BACKGROUND OF THE INVENTION
The present invention refers to an apparatus for electric stimulation and
diagnostics of the auditory nerves of a human being, in particular for
determination of sensation level, most comfortable level and uncomfortable
level curves of the auditory meatus.
In most deaf people, the transmission of electrical impulses from the
internal ear to the brain is fully functional. The reason for deafness
resides primarily in malfunctions of the so-called hair cell which is
located within the internal ear and responsible for converting mechanical
sound oscillations into electrical neural impulses. In cases of such
defects, the auditory nerves can be stimulated directly by electrical
impulses which are generated preferably by an implanted electronic
circuitry via electrodes implanted in or near the cochlea. The surgical
procedure for inserting the implant into the head is however not only
stressful to the patient but also complex and thus expensive. As deafness
may however also be the result of a defective transmission of electrical
impulses, it is indeed conceivable that without evaluation of the
functionality of the concerned auditory nerves, the implantation may turn
out to be of no value.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved apparatus
for electrical stimulation and diagnostics of auditory nerves, which
allows determination in advance, even in very sensitive and uncooperative
patients such as infants, whether the transmission of stimuli of the
auditory nerves is functional or at least sufficiently functional to
justify an artificial stimulation through implantation of cochlea
electrodes.
This object, and others which will become apparent hereinafter, are
attained in accordance with the present invention by providing a
stimulator which is adapted for detachable securement to the clothing of a
human for generating signals, electrodes placed within the human ear and
electrically connected to the stimulator by an electric conductor for
conducting the signals from the stimulator into the human ear, and a
control unit operatively connected to the stimulator for instructing the
stimulator as to characteristics of the generated signals being
transmitted.
As the stimulator for generating the required impulses is easy to handle,
the person being examined is inconvenienced only in a very minor way.
Suitably, the electrodes may be placed within the auditory meatus or in
the middle ear.
The electrodes that are placed within the auditory meatus are formed by a
body of electrically conducting material such as e.g. graphite, metal or
the like and connected via an electric conductor to the stimulator,
whereby the conductor is secured in place by an enveloping plastic body of
elastically deformable material which bears upon the inside wall of the
auditory meatus and may also be used for sealing the auditory meatus.
Thus, the stimulation impulses can be transmitted in a particular
effective manner to the auditory nerves while the elastic plastic body
securely retains the electrode in place within the auditory meatus.
When being placed in the middle ear, preferably upon the promontory, the
electrode are provided in form of a body of electrically conducting
material such as graphite, metal or the like, which is situated at the end
of an insulated metal rod with electrical conduction. The metal rod is
formed preferably in crank-like manner and is secured in place by an
enveloping plastic body of elastically deformable material that bears upon
the inner wall of the auditory meatus. If necessary, the metal rod may
further be secured by an adhesive strip upon the wall surface of the
auditory meatus. A placement of the electrode in this manner is
particularly effective to stimulate the auditory nerves.
Preferably, the control unit is of a type to enable a selection of the time
pattern as well as intensity and frequency of the stimulation signals for
wireless transmission, e.g. infrared transmission, to the stimulator.
Thus, the stimulator becomes easy to manipulate while the person being
examined retains full freedom of movement. The transmitter as well as
receiver for wireless transmission can be produced in a simple manner
while still affording the required range for use with young children.
According to another feature of the present invention, the stimulator is
equipped with means for triggering an acoustic confirmation signal when
receiving data from the control unit to effect the intended stimulation.
The generation of the acoustic signal confirms the correctness of the data
transmission in a simple manner. Preferably, the stimulator may further
include means for triggering acoustic warning signals in case of
malfunction of the intended stimulation or reception of incorrect data.
Thus, the determination of characteristic audibility curves will not be
adversely effected. Suitably, the triggered warning signal is
differentiated in dependence on the cause for malfunction. This enables
the user to pinpoint the error source as to whether it is based on
apparative malfunction, or possible screening of the receiver diode of the
stimulator, or misplaced electrodes, or even on discharged batteries.
In accordance with another feature of the present invention, the stimulator
is provided with a separate optical signaling device which triggers an
optical signal during transmission of a stimulation signal in one of both
auditory meatus or in one of both middle ears. Thus, psychological
conditioning methods as known from pediatric audiometry are employed for
reinforcing the reaction during perception of a stimulus, with the an
additional optical control of the stimulation being accomplished in a
simpler manner. The optical signaling device may be a simple toy, such as
a toy truck, which is suitable for infants. During examination, the
transmission of a stimulation signal triggers at the same time an optical
signal that draws the attention of the infant. This reaction provides the
operator with a clear and unmistakable sign that the infant senses an
auditive signal.
Suitably, the control unit includes a graphic display for illustration of
determined audibility curves and associated numerical values. Thus,
characteristic audibility curves can be monitored during examination, and
obviously erroneous values can be corrected by renewed measurements.
Advantageously, the control unit has a terminal for attachment of a
printer to thereby provide the operator with a printout of the
characteristic audibility curves as determined for the auditory meatus of
a patient.
BRIEF DESCRIPTION OF THE DRAWING
The above and other objects, features and advantages of the present
invention will now be described in more detail with reference to the
accompanying drawing in which:
FIG. 1 shows a graphical illustration as well as numerical value
illustratior of the pressure level of an audiogram of an auditory nerve
suitable for implantation, commensurate with the sensation level (SL),
most comfortable level (MCL) and uncomfortable level (UCL), expressed in
decibels as a function of the frequency in hertz (Hz), as determined by an
apparatus for electric stimulation of the auditory nerves in accordance
with the present invention;
FIG. 2a is a graphical illustration of the sensation level and
uncomfortable level of the right auditory nerve of a deaf infant,
indicating that the examined auditory nerve is most likely unsuitable for
implantation;
FIG. 2b is a graphical illustration of the sensation level and
uncomfortable level of the left auditory nerve of a deaf infant,
indicating that the examined auditory nerve is most likely unsuitable for
implantation;
FIG. 3 is a schematic illustration of a stimulator according to the present
invention as attached to the body of a patient;
FIG. 4a is a sectional view through the external and internal auditory
meatus of a human being, illustrating the placement of an electrode of the
stimulating apparatus in the external auditory meatus;
FIG. 4b is a sectional view through the external and internal auditory
meatus of a human being, illustrating the placement of an electrode of the
stimulating apparatus in the middle ear;
FIG. 5 is an exemplified, schematic illustration of the stimulating
apparatus according to the present invention in operative mode;
FIG. 6a is a schematic illustration of a control unit for use with the
stimulating apparatus according to the present invention;
FIG. 6b is a schematic illustration of the back panel of the control unit
of FIG. 6a; and
FIG. 7 is a schematic illustration of a circuitry in form of a block
diagram, showing various components of the stimulator according to the
present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The sensory perception "hearing" is created in a normally hearing human
being by the vibrations of the ear drum through sound waves that enter the
ear. These vibrations are converted in the internal ear into electrical
neural impulses which are sent to the brain via the auditory nerves for
actual recognition. In cases in which the conversion of the mechanical
oscillations of the ear drum into electrical neural impulses is defective,
no acoustic perception takes place. In deaf human beings which have such a
dysfunctional internal ear, the conversion of the sound waves can however
be assumed by an electronic circuitry by which the auditory nerves is
excited directly with electrical impulses via an electrode implanted in
the cochlea so that the hearing capability can at least be partially
restored. In order to achieve the desired results through the cochlea
implant, the auditory nerves must at least be partially functional in
order to effect a transmission of electrical impulses to the brain.
Such cochlea implants are especially suitable for deaf infants because a
successful implant of a cochlea electrode with pertaining sound converter
before the infant reaches the age of speech acquisition can prevent
muteness which is a consequence of deafness so that the child can acquire
speech in the infant stage like healthy children. The success of such
cochlea implants depends upon the functionality and ableness of the
auditory nerve so that a determination of the effectiveness of the
auditory nerve before implantation becomes desirable.
A reliable information about the functional capability of the auditory
nerves requires a determination of the sound pressure commensurate with
the so-called sensation level (SL) which is the pressure level of a sound
expressed in decibels above its threshold of audibility for the
individual, and of the uncomfortable level (UCL) of each ear. The
determination of the characteristic audibility curve of the sensation
level is effected by stimulating the auditory nerve at a certain
frequency. The intensity of the stimulation, i.e. pressure level, is then
gradually increased until the patient positively identifies an auditive
perception. This process is repeated in a same manner at different
frequencies. The connection of the family of points determined in this
manner represents the SL characteristic audibility curve.
The UCL characteristic audibility curve is determined in a same manner
whereby the sound intensity in decibels for stimulating the auditory
nerves is increased at each frequency to such a degree that the patient
experiences an uncomfortable auditive perception. The connection of the
family of points as determined in this manner represents the UCL
characteristic audibility curve.
In FIG. 1, the SL characteristic audibility curve and UCL audibility curve
are plotted by measuring range of sound intensities in decibels (db)
against the sound frequencies in hertz (Hz) in a frequency range of the
stimulation signals between 63 to 2,000 Hz for an able auditory nerve. The
area between the SL audibility curve and the UCL audibility curve
represents the MCL characteristic audibility curve (most comfortable
level) which displays those sound intensities at different frequencies
that are perceived by the patient as comfortable sound level. The
determination of the most comfortable level is however relative difficult
to ascertain in infants and is of secondary relevance for evaluating the
suitability of a cochlea implant.
FIGS. 2a and 2b depict the SL audibility curve and UCL audibility curve of
the right and left auditory nerves of a deaf infant, and it can be seen
that the suitability of the auditory nerves for a cochlea implant is at
best doubtful. An auditive perception is created in the right auditory
meatus only at a very intense stimulation at low frequencies while
frequencies exceeding 250 Hz cannot be perceived at all. The left auditory
meatus also perceives sounds only at very low stimulation frequencies.
Based on the pattern of these audibility curves, the specialist can
ascertain the appropriateness of a cochlea implant and the surgical
procedure.
The determination of these audibility curves for deaf infants has proven
very difficult up to now because of the inability to precisely ascertain
if and when an auditive perception has actually occurred. It should be
noted in this context that persons skilled in the art will understand that
the stimulation apparatus according to the present invention should not be
limited to applications with infants but is applicable for diagnostic
purposes for persons of any age group. However, since the determination of
audibility curves poses a particular problem when applied for infants, the
following description refers primarily to the use of the stimulation
apparatus for infants.
Turning now to FIG. 3, there is shown one embodiment of a stimulating
apparatus according to the present invention, including a stimulator 1
which is secured to the clothing of a child being examined and formed with
various terminals 15 for connection of conductors. Two conductors 7 are
respectively routed to the ears of the patient, and one conductor 7a is
connected to a mass electrode 9 that is attached on the skin of the
patient, e.g. of the neck.
As shown in FIG. 4a, the conductors 7 are directed into the auditory meatus
5 of each ear of the child and terminate in an electrode 3 in form of a
body of electrically conductive material such as e.g. graphite, metal or
the like. The electrode 3 is preferably of spherical configuration and
embedded inside the auditory meatus 5 within an electrolyte 6 near the ear
drum 16. The inclusion of the electrode 3 in the electrolyte 6 is
necessary to establish an effective electrical conduction between the
electrode 3 and the body mass. A preferred electrolyte 6 is for example
0.9% of saline solution. A plastic mass 8 is placed within the external
auditory meatus 5 of each ear to secure the conductors 7 and the electrode
3 in place and to possibly seal the inner ear from outside.
FIG. 4b shows a variation in which the stimulator-distal end of each
conductor 7 is widened to include a metal rod 12 and is guided through the
ear drum 16 into the middle ear comprised of the auditory ossicles 17 and
the Eustachian tube 18. Further shown in FIG. 4b is the cochlea 19 as well
as the nerves 20 and semicircular canals 26 which form the internal ear.
The metal rod 12 projects beyond the conductor 7 and terminates in an
electrode 4 which bears upon the promontory within the middle ear 14. The
electrode 4 is made of a body of conductive material such as e.g.
graphite, metal or the like and is of spherical configuration. The
placement of the electrodes 4 inside the middle ear is particular suitable
in difficult cases.
Advantageously, an adhesive strip 13 is used for properly positioning the
conductor 7 and the metal rod 12 in each ear before being secured in place
by the plastic mass 8 inserted in the auditory meatus 5.
The plastic body 8 is suitably made of elastic deformable material to
secure the conductor 7 and possibly the metallic rod 12 in place during
movements of the child. A suitable material for the plastic body 8
includes a rapidly and coldly polymerizing plastic material that resembles
those materials used for sealing the auditory meatus from sound waves.
The electric circuit triggering the stimulation impulses (stimulator 1,
electrical conductor 7, electrode 3, electrolyte 6, body of the patient),
is closed by the mass electrode 9 which is attached upon the skin of the
patient and effects a return of the stimulation currents to the stimulator
1.
The selection of parameters for the stimulation, i.e. sound frequency and
sound intensity as well as time pattern of the stimulation, is inputted
into the stimulator 1 by a control unit 2 through wireless transmission
via electromagnetic waves in the infrared range, as indicated in FIG. 5.
During examination for determination of characteristic audibility curves,
the child which is equipped with the stimulator 1 can pursue any desired
activity. As the stimulator 1 is very small and is free of any wired
connections to the control unit 2, and as the electric conductors 7 to the
various electrodes 3 or 4 and 9 are sufficiently long, the child is
afforded complete freedom of movement and the normal behavior is not
impeded in any way.
When, during playing, the child perceives an auditive signal, the activity
is interrupted, mostly followed by a particular happy facial expression. A
precise observation of the child's reactions can thus be utilized to
ascertain the threshold of audibility at each frequency and to thereby
determine the SL audibility curve. The UCL audibility curve can be
determined in a similar manner because the facial expression and the
behavior of the child changes significantly when the sound pressure
reaches the threshold of an uncomfortable sound level.
When the examination for determination of the audibility curves involves
particularly uncooperative young children, it has proven suitable to
commence the examination in such a way that the stimulation of the
auditory nerves is accompanied by an optical signal. This requires a
separate optical unit which triggers a visual signal in form of an
illuminating lamp 11 as soon as a stimulation impulse is transmitted. Any
toy with illumination, e.g. a toy truck 10, is suitable as optical unit
for infants. The triggering of a visual signal that goes hand-in-hand with
the generation of a stimulation impulse is advantageous because the child
realizes that an auditive perception is accompanied by a particular light
so that each further auditive perception will result in the child looking
for the illumination of the lamp 11. Even when shutting down the
stimulation-synchronous illumination of the light, the child will continue
to associate the auditive perception with the illumination of the lamp 11
of the toy truck 10 an thus automatically look for the lamp 11 so that the
operator assigned to the examination for determining the audibility curves
is in a position to ascertain in a particular simple manner as to whether
or not a stimulation of the auditory nerve results in an auditive
perception.
In order to check and verify a correct reception in the stimulator 1 of the
data being transmitted from the control unit 2, the stimulator 1 is
equipped with means to trigger an acoustic confirmation signal during
execution of the desired stimulation. In the event the intensity of the
stimulation current is reduced compared to the input in the control unit
2, e.g. due to discharged voltage source of the stimulator 1 or
interruption of the stimulation current, or in the event the data
transmission is upset for any reason e.g. through infrared radiation from
a TV remote control or through partial screening of the receiver diode or
transmitter diode, the stimulator 1 triggers a particular warning signal.
Turning now to FIG. 6a, there is shown a detailed illustration of the
control unit 2, including a graphic display 25 for illustration of the
determined audibility curves and selected input commands for verification
by the operator. The operation of the control unit 2 is attained by few
input keys in the following manner:
Before commencing the examination, the type of audibility curve (SL, UCL,
MCL) to be determined is selected by suitably pressing key 20. Actuation
of a key 21 situated underneath the key 20 allows a selection of which of
both electrodes 3, 4 on the left or the right side of the ear should
output the stimulation impulses. The desired sound frequency is set by the
frequency keys 22, while the sound intensities can be modified by the keys
23.
After inputting the required commands, a key 24 (so called STIM key) is
actuated for transmitting the data to stimulator 1. After conclusion of
the measurements, the result is illustrated by the graphic display 25. As
a printout of the test results is typically required, the control unit 2
is provided with a terminal 57 (FIG. 6b) for connection of a printer (not
shown). Thus, all audibility curves as illustrated by the graphic display
25 are printed also on hard copy.
FIG. 6b shows the back panel of the control unit 2, illustrating in detail
the ON-OFF switch 50, the printer terminal 57 and a bore 52 for allowing
unobstructed transmission of signals emitted from the infrared transmitter
diode 53 to the stimulator 1 for inputting desired commands.
Turning now to FIG. 7, there is shown an exemplified circuitry in form of a
block diagram for the stimulator 1. The signal as transmitted from the
control unit 2 is received by an infrared diode 30 of the stimulator and
demodulated by demodulator 31 for input into decoder 32 which translates
the inputted data in a digital data word and checks it for validity.
Subsequently, the data word is stored in register 34. If the received data
word is valid, a buzzer 38 is actuated by a respective signal via control
logic 33. Preferably, the transmission of the data word is executed twice
in series so that the sounding of two sounds confirms two successive
correct receptions.
The absence of this signal indicates a failed transmission e.g. a screening
of the receiver diode, interfering signals e.g. from a TV remote control,
etc.
The stimulator 1 further includes a frequency generator 35 which generates
a reference signal of constant frequency for input into a counter 36 for
splitting the frequency of this signal to thereby generate signals of
frequencies required for the stimulation. Bits A, B and C of the digital
data word stored in register 34 control a multiplexer 37 which connects
the frequency, commensurate with the value of A, B, C, with the reference
voltage input of a digital/analog converter (DAC) 44. The digital input of
DAC 44 is connected to the bits of the data word which determines the
sound intensity so that the output of DAC 44 generates an analog signal of
predetermined amplitude and frequency. This signal is amplified by a
current output stage 39 and connected with the electrode 3, 4 of the
desired auditory meatus (right or left) by a switch 40.
The current actually flowing through the electrode 3, 4 is sensed by a
comparator 42 for comparison with a threshold value 43. If the current
flowing through the electrode 3, 4 is too small and thus the sound
intensity of the executed stimulation insufficient, buzzer 38 is activated
by comparator 42 to trigger a respective warning signal.
While the invention has been illustrated and described as embodied in an
apparatus for electric stimulation of auditory nerves of a human being, it
is not intended to be limited to the details shown since various
modifications and structural changes may be made without departing in any
way from the spirit of the present invention.
* * * * *