Note: Descriptions are shown in the official language in which they were submitted.
CA 02757894 2011-10-05
Measurement System for Evaluating the Swallowing Process
and/or for Detecting Aspiration
Summary
The invention relates to the use of a measurement system for assessing a
process of swallowing, preferably a closure of the airway during the
swallowing
process and/or an aspiration. The measurement system can be used for sup-
porting therapy in cases of swallowing disorders and/or for diagnosing changes
in the swallowing sequence.
Description
Swallowing is one of the basic necessities of humans in order to stay alive.
Dis-
orders of this function, also referred to as dysphagia, can be fatal within a
short
period of time due to dehydration or starvation or as a result of secondary
dis-
eases such as pneumonia.
The incidence of dysphagia is high and mostly implies an acute threat to the
life
of affected patients. In the United States the percentage of patients
suffering
from swallowing disorders is about 14% in acute care hospitals and up to 50%
in
nursing homes. Aspiration pneumonia is the fourth leading cause of death
among the over 65-year-old in the United States. With 25%, stroke represents
the leading cause of all dysphagias. In England, 30,000 new patients with swal-
lowing disorders following cerebral infarction are to be expected each year.
However, both cerebral infarctions and cerebral hemorrhages can be concerned.
Within two weeks after the disease event, 41 % of the patients suffer from
symp-
toms of dysphagia, and 16% during the chronic phase. The second leading
cause of dysphagia is craniocerebral trauma. During the acute phase, a large
proportion of patients are not capable of oral food intake. After one year of
chronic stage or rehabilitation, swallowing disorders are mentioned in 10-14%
of
the cases (Winstein CJ (1983); Yorkston KM, et al. (1989)).
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Despite intensive efforts, there remains a high risk for patients with
dysphagia,
and more than 48% of aspiration pneumonias during one year following an acute
cerebrovascular disease are reported in a paper by Johnson, McKenzie and
Sievers (1993).
The central control of swallowing processes proceeds via swallowing centers in
the brain stem ("pattern generators"). These processes are stimulated, on the
one hand, by olfactory, gustatory and visual stimuli and, on the other hand,
by
the sensation of hunger, and modulated by higher suprabulbar centers. Thus,
one or more pontine, one pontine-medullary and two bulbar swallowing centers
have been postulated in the reticular formation, which are active already at
birth.
Essential to the success of swallowing is an intact interplay of the
swallowing
centers with motor and sensory cranial nerve core areas and cranial nerve fi-
bers. A disorder of the suprabulbar centers with consecutive misinformation to
the "pattern generators" leads to dysphagia.
Electromyographic measurements of the muscles in the pharyngeal-esophageal
region show that a somatotopic representation exists, which exhibits a handed-
ness-independent hemispheric difference and is asymmetric. Transfer to the
muscles proceeds via five pairs of cranial nerves (trigeminal nerve V, facial
nerve VII, glossopharyngeal nerve IX, vagus nerve X, hypoglossal nerve XII)
and
3 cervical nerves which form the cervical plexus. They are required in order
to
ensure the necessary afferents and efferents of the swallowing process which
proceeds in four or five phases.
The preparatory phase of swallowing is voluntarily controllable. The food is
intro-
duced, placed on the anterior/mid third of the tongue and examined by specific
receptors with regard to smell, taste, temperature and volume. Solid and
semiso-
lid foods are comminuted, mixed with saliva and formed into a bolus which is
en-
closed by the tongue in the anterior to mid palate area in the "tongue bowl"
at the
end of the chewing phase. The average bolus volume is 5-20 ml.
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The complex pharyngeal phase begins with the triggering of the swallowing ref-
lex and ends with the opening of the upper esophageal sphincter and takes 0.7
to 1 s. It is not voluntarily controllable. During this phase the pharyngeal
space
expands for bolus passage, pressure is built up to promote bolus
transportation,
and the airways are closed to protect against aspiration. Rapid piston-like
movements of the tongue support passage of the bolus into the hypopharynx.
Peristaltic movements of the pharyngeal wall support the piston function of
the
tongue. Depending on the bolus volume, hyoid bone and larynx move upwardly
due to contraction of the suprahyoid muscles. This motion results in an expan-
sion of space in the hypopharynx, positioning of the larynx under the root of
the
tongue to prevent aspiration, improved epiglottic tilting, and opening of the
pha-
ryngo-esophageal segment. To protect against aspiration, closure of the larynx
proceeds in 3 stages: closure of the vocal folds, vertical approach of the ad-
ducted arytenoids to the base of the epiglottis, and epiglottic tilting to
cover the
laryngeal vestibule. Closure of the epiglottis is made possible by the bolus
pres-
sure from above, the downward muscular action of the aryepiglottic muscles,
and the combined pressure as a result of the backward movement of the tongue
and the laryngeal elevation. Opening of the upper esophageal sphincter is made
possible by the anterior-superior movement of hyoid bone and larynx. The pha-
ryngeal phase ends as soon as the bolus has reached the upper esophageal
sphincter. Thereafter, the pharyngo-esophageal element, the tongue, hyoid and
larynx return to their original positions. Velopharyngeal and laryngeal
closures
open up, and the pharyngo-esophageal element is closed.
The esophageal phase begins with the closure of the pharyngo-esophageal
segment and lasts for 8 to 20 s. Bolus transportation proceeds by means of pri-
mary peristaltic waves induced by the swallowing reflex and, secondarily, by
lo-
cal stretch stimuli.
Today, different therapeutic approaches are utilized for dysphagias of
different
genesis. Apart from supportive measures such as dietary adaptation of the food
consistency, surgical procedures such as tracheotomy or placement of a PEG
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are required in cases involving marked dysphagia to prevent or minimize compli-
cations. Further measures such as surgical closure of the larynx or
laryngectomy
fall outside the standard and are used in exceptional cases only.
Conservative dysphagia therapies can be roughly classified into two
approaches.
Sensory measures (cold, heat, taste, etc.) are intended to change the
induction,
coordination or extent of a swallowing process. To this end, the exterior
and/or
interior oral region is stimulated using sensory stimuli. By changing the body
po-
sition, posture (turning the head), supportive movements (e.g. Shaker
maneuver)
or actions (e.g. Masako maneuver) during the swallowing process, motoric
measures are intended to facilitate or allow passage of food through the
pharynx
into the esophagus and reduce or prevent aspiration. Preparation and support
of
such motor skills and motoric measures involve strengthening exercises dealing
particularly with the movement of the tongue. Motoric procedures are used es-
pecially in isolated disorders, e.g. following surgery, and sensory measures
are
used in neurological diseases involving changes in perception. When dealing
with complex neurological disorders where both sensory and motor components
of the swallowing sequence are disturbed, complex therapeutic methods
(F.O.T.T.) are being increasingly used today.
In addition to various clinical examination methods attempting to assess the
risk
of aspiration in standardized food intake, two examination methods for
assessing
the swallowing process are regarded as gold standard today.
Videofluoroscopy (VFS) is an X-ray examination of the swallowing process. The
patient swallows foods including a contrast medium. The swallowing process is
recorded as a video using fluoroscopy. The examination is documented in two
planes (frontal and lateral). Slow motion resolution allows accurate
assessment
of the separate swallowing phases and possible interferences.
When using videofluoroscopy it is possible to observe the entire process of
swal-
lowing during the pharyngeal phase of swallowing. The disadvantages lie in the
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considerable technical complexity and the exposure to radiation during the ex-
amination. Automated assessment of images and analysis of results are not
possible.
In fiberoptic endoscopic examination of swallowing (FEES), the swallow is ex-
amined using a transnasally introduced, flexible endoscope. What is observed
and assessed is the ingestion of saliva and foods of varying consistency (e.g.
co-
lored water, green jello and bread). Compared to the VFS, the advantage of
this
method lies in lower exposure to radiation, so that examinations can be re-
peated, e.g. in documenting the course of a therapy. The disadvantage is that
assessments cannot be made during the oral phase and during the intradegluti-
tive pharyngeal phase, because the camera image appears white ("white out")
as a result of an approach of tongue and posterior pharyngeal wall during
actual
swallowing. Automated recording of the swallowing process is not possible in
all
its phases.
Another measuring method is electromyography (EMG). In this method, the elec-
trical activity on muscles and groups of muscles is detected. The method pro-
vides statements as to the onset and end of muscle activity and intensity of
mus-
cle contraction. The EMG is suitable for diagnosing neuromuscular diseases. At
present, EMG is rarely used to assess swallowing disorders. This method so far
has not found entrance into the diagnosis of the dynamic swallowing process.
Sonography allows real-time assessment of anatomical structures using ultra-
sound. However, sonography is of limited use for assessing swallowing disord-
ers. Possible uses are observing the tongue function during the oral phase of
swallowing and assessing the movements of hyoid bone and thyroid cartilage.
However, processes in the pharyngeal space are difficult to detect due to the
dif-
ferent types of tissue present therein.
A piezoelectric sensor can be used for detecting the upward and downward
movements of the laryngeal skeleton during swallowing. To this end, the sensor
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is placed between the cricoid and thyroid cartilage on the midline of the
neck.
Firm skin contact must be provided by means of a patch. Changes in pressure
resulting from the cricoid cartilage gliding beneath the sensor are sensed by
the
latter. As an alternative to a piezoelectric sensor, an accelerometer can be
used
to detect the movements of the larynx. The accelerometer is positioned in the
same way as the above-described piezoelectric sensor.
In the method of neck auscultation, sounds caused by swallowing are detected
on the neck using a microphone or stethoscope. At present, research is making
attempts to diagnose swallowing disorders (e.g. aspiration) through acoustic
analysis of the sounds. Furthermore, examinations relating to the coordination
of
breathing and swallowing, frequency of swallowing and detection of events in
the
swallowing process have been conducted using the auscultation method. De-
spite intensive research, only a few researchers so far have used this method
because of the uncertain results.
Kob et al. have described a multi-channel electroglottographic method which
can
be used to detect the 2D position of the larynx with a frequency of 5 Hz. The
sys-
tem described is based on U.S. Patent No. 4,909,261.
Electroglottography is primarily used to detect closure of the glottis. In a
second-
ary aspect, the measurement can be used to detect movements of the larynx.
Due to the placement of the electrodes on both sides of the larynx it is not
possi-
ble to determine the movement of other structures involved in swallowing, such
as the base of the tongue. Moreover, multi-channel electroglottography is very
complex because of the large number of electrodes being used.
The group of Kusuhara, Yamamoto, Nakamura et al. has investigated the scope
of four-electrode bioimpedance measurements of swallowing. The passive elec-
trical properties of body tissue can be summarized as bioimpedance (BI). The
BI
is detected via the voltage drop caused by a constant amplitude sinusoidal cur-
rent flow through the tissue.
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The electrodes were placed on the sternocleidomastoid muscle and the larynx
on both sides of the neck. A frequency of 50 kHz was used for BI measurement.
The measuring method was referred to as Impedance Pharyngography (IP) by
the authors. In an investigation by Yamamoto et al. the reproducibility of the
measurement curve upon slight changes in the electrode positions was deter-
mined. It was found that the curves of impedance pharyngography had nearly
identical profiles even after changing the electrode positions. The resulting
mea-
surement curve was interpreted to reflect the entire swallowing sequence
(oral,
pharyngeal, esophageal phases). Movements of larynx, pharynx, neck and eso-
phagus are regarded as the cause of change in impedance. The impedance
measurement described therein uses a grounded power source where current
flow is regulated and controlled on only one of the two current electrodes.
Such a
method may give rise to two major problems:
(1) Touching the patient during measurement, e.g. touching by a therap-
ist, may give rise to current flow through the therapist. As a consequence,
part of
the current from the controlled electrode will not flow through the patient,
result-
ing in a drop in current amplitude on the non-controlled current electrode. As
a
result, the electric field in the measurement volume undergoes massive
changes, which can lead to dramatic errors in bioimpedance measurement.
(2) Another problem with this method is that common-mode interferences
(e.g. 50 Hz mains hum) cannot be suppressed completely due to different elec-
trode-skin contact resistances on the two current electrodes. This may give
rise
to a direct current during bioimpedance measurement, so that undesirable
tissue
irritation as a result of electrolytic reaction on the electrodes may occur.
In addition, the measuring method described by the Japanese groups is not ro-
bust to low-frequency interferences not filtered out by the 25 Hz low pass
being
used. These include e.g. interferences generated by cable motion.
In collar impedance tomography, 16 electrodes are attached in a transverse
plane on the neck at the level of the thyroid cartilage and the third cervical
verte-
bra. The spatial resolution of the measurement is in the centimeter range. It
was
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found that precise determination of bolus transit times is possible by using
im-
pedance tomography, wherein the variability of the measurements is substantial-
ly smaller for larger bolus volumes (20 ml).
In this study it has been hypothesized that the change of the measured signal,
i.e. the decrease in electrical resistance, correlates with the decrease in
the
amount of air (curve volume) above the laryngeal vestibule. The curve volume
was calculated after 20% amplitude (FW20) and 50% amplitude (FW50), reveal-
ing a positive correlation between the calculated parameters and the transit
time
determined in videofluoroscopy. In addition, the results suggested a
connection
with the maximum of the amplitude and the conductivity of the solution under
in-
vestigation. It was found that the calculated results of measurement (FW20,
FW50) were dependent on the bolus volume. This also applied to the reproduci-
bility of the measured signal that increased with bolus volume. Age and gender
also had an influence on the measurement result.
In impedance tomography a very large number of electrodes are taped to the
patient's neck to observe the swallowing process. As a result of the
multiplexing
method being used, the time resolution (maximum frequency of 10 Hz) in this
measuring method is poor.
The issue of aspiration is of crucial importance for the decision whether a
patient
may receive food or must be fed through a tube or even requires tracheotomy.
Today, the VFS is regarded as gold standard when testing for aspiration. In
many cases the FEES is used in everyday clinical practice. However, the latter
allows only secondary conclusions about aspiration because the space below
the vocal cords cannot be assessed without an existing tracheotomy.
The examinations outlined above may be performed only by physicians. In many
cases, however, an assessment whether a patient should be fed orally is re-
quired in the daily practice of geriatric hospitals, nursing homes or
rehabilitation
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facilities where the technical equipment does not permit such examinations and
properly trained personnel is not available.
For safe food intake of a patient there is therefore an urgent need for a
method
allowing assessment of aspiration in a simple manner and without substantial
technical effort and risk to the patient, even in patients having limited
perception.
To protect the lungs from aspiration and pneumonia, closure of the larynx
during
the swallowing process is of crucial importance. At present, only VFS is
available
for a comprehensive survey of this process. Apart from the substantial
technical
efforts involved in VFS, the radiation exposure is a substantial drawback of
this
method. The FEES allows only secondary conclusions about the result of the
swallowing process. Since both examination methods (VFS and FEES) can only
be performed and evaluated by a physician, cost and effort required for such
ex-
aminations are high. Automated examinations that could be performed by para-
medical staff as well are not available at present. Diagnoses of swallowing
dis-
orders and exercises for improving the swallowing process are predominantly
the domain of speech-language therapists, physiotherapists and ergotherapists.
To date, there is no easy-to-use tool available that could be employed to test
the
success of a swallowing therapy using e.g. swallowing maneuvers. Also, it is
not
possible for patients to verify the success of their exercising efforts.
Automated detection of the swallowing processes is required to develop more
advanced diagnostic procedures and improved training designs.
The technical object constituting the basis of the present invention was
therefore
to develop a measurement system which could be used for the assessment of
the swallowing process and swallowing disorders such as aspiration,
penetration
or dysphagia and would not involve the disadvantages of the prior art. In
particu-
lar, the measurement system should be suitable for frequent to permanent use.
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Said object was accomplished by the independent claims, and advantageous
embodiments can be inferred from the subclaims.
In a first embodiment the invention relates to the use of a measurement system
comprising
= two elements for applying a current,
the current being applied to the neck region, and a change in bioimped-
ance being detected
= by two voltage measuring elements for
(i) detecting a closure of the airways during the swallowing process
and/or
= by two voltage measuring elements for
(ii) detecting the passage of non-gaseous substances through a cavity
partially or completely surrounded by cartilage.
It was entirely surprising that the airway closure and the passage of non-
gaseous substances through a cavity partially or completely surrounded by
carti-
lage correlated with a measurable change in bioimpedance.
The measurement system can be used transcutaneously, subcutaneously, intra-
tracheally and intraluminally. It can be utilized in the diagnosis, therapy
and pre-
vention of swallowing disorders and changes in the swallowing process, regard-
less of the underlying disease. The measurement system can also support the
training of people in which the swallowing process has changed.
It was a complete surprise to find that the inventive use of the measurement
sys-
tem can overcome the disadvantages of the prior art.
Advantageously, the use of this measurement system allows rapid and easy as-
sessment of part of or the entire swallowing process. It is particularly
advanta-
geous that the swallowing process can be assessed already during swallowing.
The measurement proceeds very rapidly, thereby making the use much easier
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because, for example, no qualified personnel is required for evaluating X-ray
im-
ages.
The new measurement system allows assessing the crucial phase of swallowing,
i.e. closure of the larynx, and thus the protection of the lower respiratory
tract.
Advantageously, the inventive use allows easy assessment of an airway closure
without exposing the patient to safety risks such as X-rays. Risks to the
patient
are excluded by the new measurement system.
The ease in handling allows uses of the measurement system that do not neces-
sarily have to be performed or supervised by qualified personnel, thereby
consi-
derably reducing the costs of applications.
Another advantage is that measurements can be made immediately at any point
in time. Preparatory measures, such as swallowing of contrast medium, are not
required. The detected change in bioimpedance can be compared with control
values. For example, it is also possible in this way to assess one's own
progress.
The measurement system is preferably used in those cases where the cartilage,
which at least in part forms a cavity, is coated with a mucous membrane. In a
particularly preferred fashion the cavity partially or completely surrounded
by car-
tilage is a larynx. By virtue of this embodiment it is possible to determine
the en-
try of non-gaseous substances into the larynx and down to the vocal folds
(pene-
tration) and/or the passage of non-gaseous substances through the larynx (aspi-
ration).
Non-gaseous substances whose passage can be determined with the measure-
ment system can be autologous secretions, such as saliva, as well as foreign
bodies. This may involve liquid materials, so that the measurement system can
be used to control drinking, for example. It is also possible to determine the
pas-
sage of solids, e.g. foods. Even small crumbs entering the trachea may have se-
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rious consequences if the patient is not able to immediately remove them e.g.
by
coughing.
Since the larynx forms the transition from the pharynx to the trachea, it is
the
earliest point where a developing aspiration and/or penetration can be
detected.
Aspiration and/or penetration can develop if the laryngeal vestibule is not
com-
pletely closed by the larynx during swallowing. Consequently, the use of the
measurement system in accordance with the invention therefore not only allows
determination of the actual aspiration or penetration, but also enables
assessing
the risk of a possibly existing aspiration and/or penetration by merely
observing
the swallowing behavior of a patient.
In a preferred embodiment the measurement system is used to determine or di-
agnose aspiration. Aspiration may have life-threatening consequences so that
rapid recognition thereof is of crucial importance. In this way it is possible
to
judge whether a patient is able to ingest food or artificial feeding is
necessary. To
date, such assessments frequently had to be made by feel, because the measur-
ing methods required could be performed only by a physician and were therefore
not sufficiently available in many institutions (such as nursing homes). Being
non-invasive and very simple to use, the measurement system according to the
invention does not require a physician for transcutaneous use. The new method
allows detection of perilous transition of liquids, saliva or food into the
trachea
without substantial technical effort or hazardous investigations such as X-
ray.
In a preferred embodiment, the measurement system is used to determine pene-
tration. Penetration involves entry of non-gaseous substances into the upper
respiratory tract. The determination of penetration can therefore be used to
con-
trol the swallowing process and identify the risk of possible aspiration at an
early
stage.
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In a particularly preferred embodiment the invention relates to the use of the
measurement system, wherein the change in bioimpedance during the approach
of larynx and hyoid bone is determined.
Quite surprisingly, the approach of larynx and hyoid bone results in a change
in
bioimpedance in the neck, which can be measured through the inventive use of
the measurement system. This distinguishes the invention from previously
known BI measuring methods. Thus, the decisive phase of the swallowing
process, namely, closure of the airways by the approach of larynx and hyoid
bone, can be assessed with the measurement system according to the invention.
Also preferred is a use of the measurement system, wherein
= the voltage measuring elements are each arranged in a voltage measuring
electrode, and
= the elements for applying a current are each arranged in a current elec-
trode.
This embodiment can be used transcutaneously, subcutaneously, intratracheally
as well as intraluminally. The advantage of this use is that the system
furnishes
particularly precise data and can be adapted to the anatomy of any patient
with-
out great effort.
More specifically, there are two possible procedures of measuring the BI. In
the
2-electrode method, the voltage is measured directly via the current
electrodes,
the voltage drop being measured simultaneously via the electrode-skin contact.
The voltage drop is caused by the current flow generated in the patient via
the
current electrodes. This resistance varies with time and therefore leads to
mea-
surement errors. Such an undesirable effect can be avoided by using the 4-
electrode method where the voltage is measured via additional electrodes. Be-
cause the current flowing through the voltage electrodes is negligible, there
is no
interfering time-varying voltage drop as a result of electrode-skin contact.
The
preferred embodiment of the measurement system supports both methods.
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Surprisingly, the measurement system can also be used to determine the ap-
proach of larynx and hyoid bone and the aspiration and/or penetration at the
same time. Aspiration can occur if the larynx is not properly closed during
swal-
lowing. For this reason, swallowing disorders, such as dysphagia, and
aspiration
or penetration can be mutually dependent. Simultaneous assessment may there-
fore be advantageous. Allowing detection of both sufficient closure of the
larynx
during the swallowing process and passage of non-gaseous substances through
the larynx, this use is particularly suitable for the assessment of swallowing
be-
havior and/or the diagnosis, therapy or prevention of aspiration, penetration
and/or dysphagia. The measurement system is superior to the known systems
because dysphagia as well as aspiration or penetration can be detected in a
par-
ticularly uncomplicated way. Thus, the measurement system of the invention al-
lows detection of a predestination for aspiration as well as the aspiration
itself.
It may be advantageous for this use of the measurement system to have two
power sources which in this case must differ in their frequency range so that
the
two BI measuring methods do not influence each other. Preferably, one bioim-
pedance measurement is performed at 50 kHz and the other bioimpedance
measurement is preferably carried out at 100 kHz.
The established correlation between BI change and larynx-hyoid distance allows
automated assessment of the swallowing process, which can be used in visual
representation or to control other devices (screen display, stimulators). This
opens up completely new possibilities for the diagnosis, therapy and
prevention
of swallowing disorders.
For use of the measurement system the current electrodes in a particularly pre-
ferred embodiment are arranged on both sides on the sternocleidomastoid mus-
cle at the level of the lower jaw and/or on the thyroid cartilage at the level
of or
below or above the vocal cord plane.
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These positions were found to be particularly advantageous because the mea-
surement values obtained were particularly accurate.
The arrangement of the current electrodes on both sides on the sternocleido-
mastoid muscle at the level of the lower jaw is particularly suitable for use
of the
measurement system for determining the closure of the airways during the swal-
lowing process. Surprisingly, these positions are also particularly
advantageous
for use of the measurement system for simultaneous assessment of the closure
of the airways during the swallowing process and determination of aspiration
and/or penetration.
Arrangement of the current electrodes on the thyroid cartilage at the level of
or
below the vocal cord plane was found to be advantageous for use of the mea-
surement system for determining aspiration. Penetration could be detected par-
ticularly well when the current electrodes were arranged on the thyroid
cartilage
above the vocal cord plane.
It is also particularly preferred to use the measurement system in such a way
that the voltage measuring electrodes are arranged on both sides between the
hyoid bone and thyroid cartilage in front of the sternocleidomastoid muscle
and/or on the thyroid cartilage at the level of or below or above the vocal
cord
plane.
It was found that the change in bioimpedance during the approach of larynx and
posterior hyoid bone can be detected particularly well when the voltage measur-
ing electrodes are arranged on both sides between the hyoid bone and thyroid
cartilage in front of the sternocleidomastoid muscle.
The arrangement of the voltage measuring electrodes on the thyroid cartilage
at
the level of or below the vocal cord plane has proven particularly suitable
for de-
termining the risk of aspiration. By arranging the voltage measuring
electrodes
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on the thyroid cartilage above the vocal cord plane, particularly advantageous
measurement of the change in bioimpedance during penetration is possible.
In another preferred embodiment the invention relates to the use of the mea-
surement system, wherein one voltage measuring element and one element for
applying a current are arranged together in a single electrode. This measure-
ment system can be used transcutaneously, subcutaneously, intratracheally or
intraluminally. This embodiment is advantageous because the use thereof is
quite agreeable for a patient and is not considered annoying. Owing to its com-
pact design, the system is suitable for mobile use, can be easily transported
and
is particularly easy to use by patients themselves.
This embodiment is also advantageous in applications where permanent detec-
tion is required, such as detection of saliva passage. Reducing the number of
electrodes required is particularly suitable for subcutaneous, intratracheal
or
intraluminal application, because the measurement system can be applied gently
and is not felt as painful or considered annoying.
In another particularly preferred embodiment the electrodes, each comprising a
voltage measuring element and an element for applying a current, are arranged
on both sides in front of the sternocleidomastoid muscle between the hyoid
bone
and thyroid cartilage or on both sides on the thyroid cartilage at the level
of or
below or above the vocal cord plane. This arrangement is particularly well
suited
to detect passage or penetration of non-gaseous substances through the larynx.
Surprisingly, this arrangement also allows detection of extremely small
volumes,
so that the passage of small amounts of liquid or crumbs can be detected.
In particularly preferred embodiments, aspiration is determined using one of
the
following electrode arrangements:
Four electrodes (two current electrodes and two voltage measurement
electrodes) are attached transcutaneously, essentially along a line, on both
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sides of the thyroid cartilage at the level of or below the vocal cord plane.
For particularly precise measurement, the two outer electrodes are prefer-
ably current electrodes.
Two electrodes, each comprising a voltage measurement element and an
element for applying a current, are attached transcutaneously on both
sides of the thyroid cartilage at the level of or below the vocal cord plane.
Two current electrodes and two voltage measurement electrodes are ar-
ranged subcutaneously on, in or through the thyroid cartilage at the level of
or below the vocal cord plane, the two outer electrodes preferably being
current electrodes.
Two electrodes, each comprising a voltage measurement element and an
element for applying a current, are arranged subcutaneously on, in or
through the thyroid cartilage at the level of or below the vocal cord plane.
Two current electrodes are located on or in a tracheal cannula, while two
voltage measurement electrodes are arranged transcutaneously on the thy-
roid cartilage at the level of or below the vocal cord plane or subcutaneous-
ly on, in or through the thyroid cartilage.
Two electrodes, each comprising a voltage measurement element and an
element for applying a current, are located on a tracheal cannula.
In particularly preferred embodiments, penetration is determined using one of
the
following electrode arrangements:
Four electrodes (two current electrodes and two voltage measurement
electrodes) are attached transcutaneously, essentially along a line, on both
sides of the thyroid cartilage above the vocal cord plane. For particularly
CA 02757894 2011-10-05
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precise measurement, the two outer electrodes are preferably current elec-
trodes.
Two electrodes, each comprising a voltage measurement element and an
element for applying a current, are attached transcutaneously on both
sides of the thyroid cartilage above the vocal cord plane.
Two current electrodes and two voltage measurement electrodes are ar-
ranged subcutaneously on, in or through the thyroid cartilage above the
vocal cord plane, the two outer electrodes preferably being current elec-
trodes.
Two electrodes, each comprising a voltage measurement element and an
element for applying a current, are arranged subcutaneously on, in or
through the thyroid cartilage above the vocal cord plane.
Two current electrodes are located on or in a tracheal cannula, while two
voltage measurement electrodes are arranged transcutaneously on the thy-
roid cartilage above the vocal cord plane or subcutaneously on, in or
through the thyroid cartilage.
Two electrodes, each comprising a voltage measurement element and an
element for applying a current, are located on a tracheal cannula.
In particular, cannulas/tubes and sensors should be used if already
present. Items already present in the neck can thus be used with advan-
tage. Applications are possible even when measuring via the cannula alone
(e.g. measurement of aspiration with cannula or tube in position; flow pass-
ing despite cannula).
CA 02757894 2011-10-05
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In particularly preferred embodiments the swallowing process, preferably the
approach of larynx and hyoid bone, is assessed using one of the following elec-
trode arrangements:
The current electrodes are attached transcutaneously on both sides on the
sternocleidomastoid muscle at the level of the mandibular angle, while the
voltage measurement electrodes are arranged on both sides between the
hyoid bone and thyroid cartilage in front of the sternocleidomastoid muscle.
The electrodes, each comprising a voltage measurement element and an
element for applying a current, are transcutaneously attached laterally on
both sides of the neck in front of the sternocleidomastoid muscle between
hyoid bone and thyroid cartilage.
The current electrodes are attached subcutaneously on both sides on the
sternocleidomastoid muscle at the level of the mandibular angle, while the
voltage measurement electrodes are arranged subcutaneously at the level
of the epiglottic vallecula.
The electrodes, each comprising a voltage measurement element and an
element for applying a current, are attached subcutaneously at the level of
the epiglottic vallecula.
Two current electrodes are arranged on a sensor located in the pharynx,
while the two voltage measurement electrodes are attached transcuta-
neously between hyoid bone and thyroid cartilage or subcutaneously at the
level of the epiglottic vallecula.
Each electrode comprises a voltage measurement element and an element
for applying a current, and one electrode is arranged on a sensor located in
the pharynx, while the other electrode is attached subcutaneously between
CA 02757894 2011-10-05
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hyoid bone and thyroid cartilage or subcutaneously at the level of the epi-
glottic vallecula.
In particularly preferred embodiments the swallowing process, preferably the
approach of larynx and hyoid bone, is assessed, while the incidence of aspira-
tion and/or penetration is determined at the same time, using one of the
following
electrode arrangements:
When using a measurement configuration with only one power source, two
transfer bioimpedances are measured with respect to this power source.
The current electrodes are attached transcutaneously on both sides on the
sternocleidomastoid muscle at the level of the mandibular angle, while two
voltage measurement electrodes are attached transcutaneously on both
sides between hyoid bone and thyroid cartilage in front of the sternoclei-
domastoid muscle and two additional voltage measurement electrodes are
attached transcutaneously on both sides on the thyroid cartilage at the lev-
el of or below or above the vocal cord plane.
The current electrodes are attached subcutaneously on both sides on the
sternocleidomastoid muscle at the level of the mandibular angle, while two
voltage measurement electrodes are attached subcutaneously at the level
of the epiglottic vallecula and two additional voltage measurement elec-
trodes are attached subcutaneously at the level of or below or above the
vocal cord plane.
The current electrodes are located on or in a pharyngeal sensor or on or in
a tracheal cannula, while two voltage measurement electrodes are at-
tached subcutaneously at the level of the epiglottic vallecula and two addi-
tional voltage measurement electrodes are attached subcutaneously at the
level of or below or above the vocal cord plane.
CA 02757894 2011-10-05
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It is also possible to combine all the above-mentioned arrays for assessing
the swallowing process with all the above-mentioned arrays for determining
aspiration or penetration, in which event one bioimpedance measurement
is preferably carried out at 50 kHz and the other bioimpedance measure-
ment preferably at 100 kHz. Advantageously, this prevents mutual influ-
ence of the two BI measurement procedures, which would falsify the mea-
surement result.
The respective terms have a generally accepted meaning in the relevant field
of
the art, so that a person skilled in the art will be able to implement the
above-
mentioned uses of the measurement system.
The positions specified herein are particularly suited to obtain precise
measure-
ment values because large amplitudes can be achieved. Furthermore, no false-
positive or false-negative results are generated with the measurement arrays
specified above. Also, these positions are well-suited for the applications
men-
tioned above because the electrodes can be arranged on the appropriate spots
in an uncomplicated manner and do not slip as a result of the swallowing
process or breathing movements. A person skilled in the art will interpret the
technical teaching of the present invention in such a way that the anatomy of
a
patient may require slight variations in the positions of the electrodes in
accor-
dance with gender, height, weight and age. A person skilled in the art will be
able, depending on the anatomical preconditions of the individual patient, to
ar-
range the electrodes in such a way that optimum measurement is possible.
In another preferred embodiment the invention relates to the use of the mea-
surement system, which system additionally includes neuromuscular stimulators.
Thus, the measurement system is not only usable in the determination of swal-
lowing disorders, dysphagia, aspiration and/or penetration, but is also
capable of
initiating appropriate counter measures. When aspiration and/or penetration oc-
cur, swallowing, coughing or clearing the throat can be initiated by
appropriate
stimulation, for example. The data obtained from the measurements can be used
CA 02757894 2011-10-05
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to control different types of stimuli, e.g. electrically, mechanically,
chemically
(e.g. citric acid), thermally or by means of vibration, to make the process of
swal-
lowing safer.
It is possible, for example, to stimulate the digastric muscle, geniohyoid
muscle
and/or thyrohyoid muscle. In addition, a cough can be triggered by stimulating
the superior laryngeal nerve, the vagus nerve and/or stretch receptors of the
tra-
chea. To this end, the stimulation pulses are generated using a multichannel
stimulator for neuromuscular stimulation.
The method represents a significant advance in the diagnosis of life-
threatening
aspiration. When detecting aspiration, it is possible to identify undiscovered
aspi-
ration ("silent aspiration") which is especially dangerous to a patient due to
the
absence of defensive reactions (coughing, clearing the throat) protecting the
pa-
tient. Coughing can be induced by triggered stimulation (electrical, chemical,
mechanical, etc.). The invention not only enables easier detection of
aspiration,
but also allows triggering a defensive reaction without significant time
delay, so
that the risk of developing secondary diseases is notably minimized.
In a preferred fashion the measurement system is used in the form of a neural
prosthesis for subcutaneous, intratracheal or intraluminal application. This
em-
bodiment is particularly suitable for continuous use, allowing e.g. permanent
con-
trol of the swallowing process by the patient. Quite surprisingly, it was
possible to
design the measurement system of the invention in such a way that successful
implantation in a patient can be made without any complications or impairment
of
the patient.
The use of a neural prosthesis for the treatment of swallowing disorders is of
enormous clinical significance, providing a new, forward-looking perspective
in
the rehabilitation of swallowing disorders. To date, there are only few valid
the-
rapeutical options for the treatment of neurogenic dysphagia. In most cases of
patients suffering from severe dysphagia, diagnosis is followed by application
of
CA 02757894 2011-10-05
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a tracheal cannula to minimize aspiration and use of a PEG (percutaneous en-
doscopic gastrostomy) to maintain food intake. In addition, an intensive,
lengthy
rehabilitation therapy with uncertain outcome is necessary. This process often
takes years to complete. During this period, the patient is dependent on 24-
hour
care, rehabilitation and medical aid. This represents a significant burden to
pa-
tients, relatives and cost centers. By virtue of the supporting measures of
con-
trolled stimulation as part of a neural prosthesis, it is possible to change
and
shorten this course, which means significant reduction of the impairment and
im-
provement of the quality of life for the patients and substantial savings for
cost
centers.
A preferred embodiment of a measurement system in accordance with the inven-
tion is shown in Figure 2. To protect the measurement amplifier against the
high
voltage of the stimulation pulses, the input of the amplifier is protected.
Such pro-
tection can be achieved by using stimulation pulse-triggered switches, diodes
or
the like. It is preferred to use a combination of resistors and diodes. In a
pre-
ferred fashion, resistors are arranged at the input of the measurement
amplifier,
followed by diodes capable of draining off the high voltage drops on the
voltage
electrodes. In addition, such protection prevents dangerous leakage currents
to
the patient. The output of the power source is protected by diodes capable of
draining off the high voltage drops on the current electrodes.
In addition, the system was designed for use with neuromuscular stimulators.
Such stimulation systems are being used in the therapy of swallowing disorders
or in neuroprosthetic assistance for dysphagia patients.
In another preferred embodiment the invention relates to the use of the mea-
surement system for producing a means for the assessment of the swallowing
process, supporting the therapy of swallowing disorders and/or diagnosing
changes in the swallowing process.
CA 02757894 2011-10-05
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In another preferred embodiment the invention relates to the use of the mea-
surement system for producing a means for the diagnosis, therapy and/or pre-
vention of aspiration, penetration and/or dysphagia.
It is preferred to use a measurement system at a frequency of 25 kHz to
200 kHz, preferably 50 kHz or 100 kHz.
It is also preferred to use a bandpass filter. In this way it is possible to
remove
disturbing artefacts and isolate the measuring frequencies.
The bandpass filter is preferably inserted downstream of the measurement am-
plifier. Disturbing artefacts on the voltage measuring elements, which may be
caused by muscle action potentials and cable movement, can be easily removed
by means of the bandpass, because the changes in BI are included in the ampli-
tude-modulated voltage within a narrow frequency range around the selected
measurement frequency.
Furthermore, this measuring method is more robust to external interference and
has higher time resolution than, for example, electrotomography and multi-
channel electroglottography.
Also preferred is the use of the measurement system for EMG measurement, in
which event a low-pass filter with preferably 12 kHz is used. The low-pass
filter
allows isolation of the measurement frequency and thus removal of disturbing
ar-
tefacts. The low-pass filter is preferably inserted downstream of the measure-
ment amplifier. The BI measuring voltages on the voltage measuring elements,
which may be caused by the power source, can be easily removed by means of
the low pass, because the muscle action potentials are included in the
selected
measurement frequency.
The EMG allows measurement of existing muscle activity during the swallow and
thus provides further information for assessing the swallowing process. Owing
to
CA 02757894 2011-10-05
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the simultaneous measurement on the voltage electrodes, use of additional elec-
trodes is not required.
Particularly advantageous is a use wherein at least one differential power
source
is used, which symmetrically controls the floating load, minimizes and
preferably
suppresses common-mode interference, allows essentially no DC component,
and is robust to grounding the load to earth. This embodiment is advantageous
because it largely prevents DC currents during measurement and measurement
errors as a result of patient contact and is robust to grounding the load to
earth.
It is particularly preferred to use a power source in accordance with DE 601
25
601 T2. The DE 601 25 601 T2 is hereby incorporated in the disclosure of the
present invention.
It is also preferred to use a direct current barrier to the patient. The DC
barrier is
preferably placed on both outputs of the power source. The DC barrier is
prefer-
ably arranged downstream of the diodes used for surge protection. In preferred
embodiments, capacitors, preferably Y1 capacitors, are used as DC barrier. It
is
also preferred to use complete galvanic insulation of each differential power
source.
The circuit-technical implementation of the BI measurement is simplified be-
cause only the changing magnitude of the BI needs to be determined. The
course thereof can be obtained from the envelope of the measured voltage. It
is
also preferred to use a measurement system wherein the magnitude of the bio-
impedance is determined via amplitude modulation, preferably using an
envelope detector.
By controlling two current flows via both current electrodes, it is possible
to avoid
some of the problems of the prior art. While touching the patient during mea-
surement likewise results in current flow through the therapist, this flow is
com-
pensated by readjusting the current flow, thereby eliminating one major source
of
error.
CA 02757894 2011-10-05
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To avoid a voltage drop of the changing electrode-skin impedance and the asso-
ciated measurement error, it is preferred to use the 4-electrode method for
tran-
scutaneous measurements.
In another preferred embodiment the invention relates to the use of the mea-
surement system, wherein the change in bioimpedance is displayed visually,
preferably on a monitor. The data obtained from the measured values can be
used for visual representation to assist the patient in performing exercises
as
part of a therapy. This embodiment is advantageous because it allows monitor-
ing which need not be supervised by a physician or specialist personnel.
In another preferred embodiment, a reference generator ("right leg drive") can
be
used. This circuit ensures that capacitively coupled common-mode interference
is prevented or at least reduced.
Thus, alternatively, it is possible with advantage to perform the measurement
without a reference electrode when instead activating an active circuit for
com-
mon-mode reduction at the inputs of the voltage measuring circuit. The
principle
of "active shielding" is used to reduce the capacity of the measurement cable,
involving active generation of a shield voltage which is applied to the cable
shield
of the voltage measurement elements.
Accordingly, the invention relates to a measurement system for use in
assessing
a swallowing process, said system comprising:
= two elements for applying a current,
the current being applied to the neck region, and a change in bioimped-
ance being detected
= by two voltage measuring elements for
(i) detecting a closure of the airways during the swallowing process
and/or
= by two voltage measuring elements for
CA 02757894 2011-10-05
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(ii) detecting the passage of non-gaseous substances through a cavity
partially or completely surrounded by cartilage.
The above explanations for the use of the system also apply to the system for
use in assessing a swallowing process.
Other advantages of the invention are as follows:
= Easy handling
= Low risk to the patient
= Reliable assessment
= Measurement is possible over 24 hours and 7 days a week.
= BI measurement allows unattended monitoring and recording of the swal-
lowing process and/or aspiration
= The system can be used for therapy monitoring.
Examples
Example 1
In a pilot study, two patients with normal swallowing who had to undergo an X-
ray examination with contrast medium for diagnosing their malignant disease
were simultaneously subjected to a BI measurement wherein the change in BI
magnitude was measured using the 4-electrode method. The voltage measure-
ment electrodes were adhered on both sides at the level of the thyroid
cartilage
posterior horn. Current was fed on both sides through electrodes on the
sternoc-
leidomastoid muscle. Figure 1 exemplifies the electrode positions/points of
mea-
surement.
The amplitude of the sinusoidal current was 0.25 mA, and the frequency was
50 kHz. The four-electrode method with separate transcutaneous current elec-
trodes and voltage electrodes was chosen in order to avoid voltage drop of the
changing electrode-skin impedance and associated measurement errors. In the
CA 02757894 2011-10-05
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event of an implanted measurement system, it is also possible to use a two-
electrode measurement array (where current electrodes and measurement elec-
trodes are identical).
The hypothesis to be tested in the pilot study was whether assessment of a la-
ryngeal closure could be made by means of a bioimpedance measurement. The
distance between the posterior thyroid cartilage (larynx) and the hyoid bone
(hyoid) was used as a reference for laryngeal closure (see Figure 3).
Figure 4 shows the change in bioimpedance magnitude versus time. Compared
to the simultaneous radiological examination, it was found that the
bioimpedance
magnitude decreases when the anatomical structures approach each other (see
Figure 5). The amplitude of the BI correlates with the degree of airway
closure.
Linear regressions of BI change and distance yielded the correlation
coefficient
Rs,,bject 1 = 0.65 and Rsubject 2 = 0.51.
Example 2
Using the 4-electrode method, the change in BI magnitude was measured on a
bovine larynx. The voltage measurement electrodes were attached to both sides
at the level of the arytenoids in the muscles. Current was fed on both sides
through electrodes inserted in the thyroid cartilage (no passage of the
electrodes
into the cavity). Figure 6 exemplifies the electrode positions and points of
mea-
surement.
The four-electrode method (separate electrodes for current feeding and voltage
measurement) was used for measurement, but it is also possible to use a two-
electrode measurement array (where current electrodes and measurement elec-
trodes are identical).
The amplitude of the sinusoidal current was 0.25 mA, and the frequency was
50 kHz.
CA 02757894 2011-10-05
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The hypothesis to be tested was whether passage of non-gaseous substances
through the larynx would result in a change in bioimpedance. The results of an
experimental series of measurements are shown in Figures 7 to 12. It was found
that the impedance changes depending on the selected fluids. A specific mini-
mum can be observed for each individual fluid, which depends on the ionic
charge (conductivity) of the fluid. The measurement curve returns to the
starting
point after passage of the fluids, and there are no summation effects.
Figures 7 through 11 show the passage of fluids through the larynx. Shown are
the measurement curve (top left), the clamped bovine larynx (top right), the
video
image with a view inside the larynx and the names of the fluids (bottom left),
and
a schematic representation of the measuring point level (bottom right).
Figure 7: Identifies the starting point.
Figure 8: Yogurt enters the larynx.
Figure 9: Yogurt is located at the level of the vocal cords, just above the
measurement points, a marked change of the measurement curve
is seen.
Figure 10: The yogurt is rinsed down with water, the measurement curve
reaches its minimum upon passage beyond the measurement
points.
Figure 11: The measurement curve returns to the starting point as soon as
the larynx is empty.
Figure 12: Shows the passage of various fluids through the larynx (Al Water,
B yogurt, A2 water, C buttermilk). In each case the minimum de-
scribes the passage of fluid beyond the point of measurement.
CA 02757894 2011-10-05
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Reference numerals
Laryngeal vestibule
11 Current electrodes
12 Reference electrode
13 Voltage electrodes
14 Trachea
