Eustachian tube function
Eustachian tube function testing Embryology of the Eustachian tube: During the first 10 weeks of gestation lateral extension of the endoderm of the first pharyngeal pouch as it touches the inner surface of the ectoderm of the first branchial arch occurs. Expansion of the distal portion of the pouch forms the tubotympanic recess (future middle ear cavity) while the proximal portion narrows to form the Eustachian tube.
Later on the muscle of the tube develops from the surrounding mesoderm. The levator veli palatini and tensor veli palatini muscles develop before the cartilage and glandular tissue.
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Eustachian tube function
During the middle and third trimester the cartilaginous portion of the tube develops to reach 1/3 mm in length at term. Whenever, the angel of the tube gradually changes from horizontal to oblique after birth through adulthood. Anatomy of the Eustachian tube:
The adult Eustachian tube is 36 mm long and directed downward, forward and medially from the anterior wall of the middle ear forming a 45o angel. It enters the naso-pharynx 1.25 cm behind posterior end of inferior turbinate. The lateral 1/3 is bony and arises from the anterior wall of the middle ear and the medial 2/3s are fibro-cartilaginous entering the nasopharynx. 2
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Eustachian tube function
The bony portion passes through the squamous and petrous portions of the temporal bone. It is wide at its tympanic end and narrows gradually to the isthmus (the narrowest part) where the apex (lateral end of the cartilaginous part) of the tube joins the bony part. The cartilaginous portion consist postero-medially from a plate of cartilage which bends forward and forms a short flange while the antero-medial wall is formed partially from fibrous tissue. It is attached to the skull base in a groove between the petrous part of the temporal bone and greater wing of the sphenoid. The wide medial end of the Eustachian tube lies under the mucosa of the nasopharynx raising the mucosa to form the tubal elevation (torus tubarius).
N.B. The fossa of Rosenmüller lies just behind this elevation and is considered a common site of origin for nasopharyngeal carcinoma and occult primary tumors.
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Eustachian tube function
The Eustachian tube has a triangular lumen, measuring 2-3 mm vertically and 3-4 mm horizontally. The bony portion is always open; while the fibrocartilaginous portion is closed at rest and opens only on swallowing, yawning, or forceful inflation. Mucosal lining of the Eustachian tube consists of respiratory epithelium at its nasopharyngeal opening which include columnar ciliated cells, goblet cells, and mucous glands. The respiratory epithelium blends with the middle ear mucosa in the bony portion of the tube.
The infantile tube: 18 mm in length (half the size of the adult one), more horizontal and less angulated. The bony portion is relatively longer and wider in diameter, the nasopharyngeal end of the cartilaginous portion lies more inferiorly. Moreover, the posterior wall of the Eustachian tube is longer than the anterior wall and has more mucosal folds (microturbinates) in children than in adult which provide important protection and clearance functions.
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Eustachian tube function
Ostmann fat pad: is a pad of fat located in the inferolateral aspect of the Eustachian tube and playing an important contributing factor in closing the orifice and contribute in the protection of the Eustachian tube and the middle ear from retrograde flow of nasopharyngeal secretions. Muscles of the Eustachian tube: A. Tensor veli palatini: o Origin:
From the bony wall of the scaphoid fossa.
The whole length of the cartilaginous flange that forms
the upper portion of the front wall of the cartilaginous tube. o Course:
Runs downwards converging into a short tendon.
The tendon runs medially around the pterygoid hamulus.
Fans out within the soft palate and mingles with fibers of
the other side in the midline raphe. 5
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Eustachian tube function
o Relations: separates the tube from the otic ganglion, the mandibular nerve and its branches, the chorda tympani nerve and the middle meningeal artery. B. Salpingopharyngeus muscle: A delicate muscle. Attaches to the pharyngeal end of the Eustachian tube. Blends with the palatopharyngeus muscle downwards. C. Levator veli palatini muscle: o Origin:
The lower surface of the cartilaginous portion of the tube.
The lower surfaces of of the petrous bone.
Functions of the Eustachian tube muscles:
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Help open and close the tube.
Help it perform its function. Dr-Ebtessam Nada
Eustachian tube function
Eustachian tube blood vessels:
The ascending pharyngeal and middle meningeal arteries.
Venous drainage via the pharyngeal and pterygoid plexus
of veins.
Lymph drainage through the retropharyngeal lymph
nodes. N.B. The junctional part of the Eustachian tube is a safe landmark to identify and protect the internal carotid artery during cranial base surgeries. Nerve supply:
Pharyngeal branch of the sphenopalatine ganglion (from
the maxillary artery) supplies the ostium.
The nervous spinosus derived from the mandibular nerve
supplies the cartilaginous part.
The tympanic plexus (from the glossopharyngeal nerve)
supplies the bony part. Functions of the Eustachian tube: a. Ventilation or pressure regulation of the middle ear:
Opening of the Eustachian tube actively maintains normal
atmospheric pressure.
Normally the bony part is always open and the
cartilaginous part is collapsed at rest, with slight negative middle ear pressure.
The Eustachian tube opens during swallowing or yawning
by contraction of the tensor veli palatini muscle. The role of the 7
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Eustachian tube function
levator veli palatini muscle is unclear (passive opening of the tube is caused by contraction of this muscle).
N.B. closure of the cartilaginous part is caused by elastic recoil of elastin hinge and the deforming force of Ostmann’s fat.
Ventilator function is less efficient in children than in
adults. Together with repeated upper respiratory tract infections and enlarged adenoids in children, increased incidence of middle ear disease occur. Improvement of tube function occurs as children grow. b. Protection of the middle ear from
Sudden loud sounds: The Eustachian tube is closed at
rest and thus loud sounds are dampened before reaching the middle ear through the nasopharynx.
The ascending secretions of the naso-pharynx: The
Eustachian tube drains normal secretions of the middle ear into the nasopharynx by the mucociliary transport system and by repeated active tubal opening and closing and prevent ascending secretions from the naso-pharynx from entering the middle ear due to narrow isthmus and angulation between the 2 parts at the isthmus.
Laryngopharyngeal reflux (LPR) was recently implicated in the etiology of otitis media with effusion (OME).
Protect the middle ear by the local immunologic defense
of the respiratory epithelium of the Eustachian tube, as well as its mucociliary defense (clearance).
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Eustachian tube function
c. Clearance or drainage of middle ear secretions into the nasopharynx: 1. Drainage of secretions and occasional foreign material from the middle ear is achieved by:
The mucociliary system of the Eustachian tube.
The middle-ear mucosa and muscular clearance of the Eustachian tube. Surface tension within the tube lumen. 2. The tensor veli palatini muscle actively opens the nasopharyngeal orifice of the Eustachian tube.
N.B. A relative negative middle ear pressure, as occurs in aircraft or scuba diving descent, may lock the Eustachian tube which leads to stagnation of secretions, and effusion collects in the middle ear as otitic barotrauma evolves. Inflation of the Eustachian tube by the Valsalva maneuver or by politzerization can break the negative pressure in the middle ear and clears the effusion.
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Eustachian tube function
Eustachian Tube Function Tests:
N.B. a fully patent Eustachian tube does not mean that it is working properly, as occurs with patulous Eustachian tube and mucociliary abnormalities so, examination is for patency and function. A. Examination
of
Eustachian
tube
functions
with
perforated TM:
Objectives: to predict the outcome of surgical repair of TM. a. Fistula test: applying positive pressure in the external canal by tympanometry probe.
b. Inflation deflation test: Definition: it is a primarily measure of active ET function, although passive opening can be measured. Principle: application of positive pressure to the middle ear (inflation) forces the Eustachian tube open. Procedure (Intratympanic manometry): As it employs measurement of middle ear pressure directly in the middle ear (perforated TM). A positive pressure is applied to the middle ear via a sealed probe in the ear canal, and this is increased either to a defined point (typically 100 –300 mm H2O) or until the ET passively opens. The patient is then asked to swallow repeatedly until no further middle ear pressure changes are detected, and the ‘residual pressure’ plateau is reached.
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The procedure is then repeated by applying a negative pressure of similar magnitude. The residual pressure and number of swallows required to reach it are recorded.
c. Valsalva maneuver: inflation of the middle ear and Eustachian tube by forced expiration with the mouth closed and the nose pinched by the thumb and forefinger.
The high positive pressure in the nasopharynx affects the proximal end of the tube and sound of the air escaping from the middle ear can be heard with stethoscope or Toynbee tube and if the ear is discharging bubbles can be seen. Contra-indications: Atrophic scar of the TM (possible rupture). Spread of infection from the nose and nasopharynx. 11
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d. Forced Response Test:
Measures the pressure at which the ET opens passively
when the middle ear pressure is increased.
It is primarily a test of passive ET opening, which requires
a TM perforation or ventilation tube without otorrhea.
A sealed probe in the external auditory canal is used to
increase middle ear pressure until the ET is forced open.
Air delivery is continued in an attempt to establish a
stable middle ear pressure due to a steady flow out via the ET.
If the air flow is stopped, the pressure at which the ET
closes can be recorded and used as an outcome variable along with the tube opening pressure, steady state pressure and calculated resistances.
The test can be performed at different air flow rates, and
swallowing during the steady state period can provide further information on active ET function and the effect this has on tubal resistance.41 e. Clearance Test: Contrast medium was instilled into the middle Contrast medium was instilled into the middle ear via a drumhead perforation and 1 scan/sec ear via a drumhead perforation and 1 scan/sec taken during swallowing taken during swallowing. i.
Movement of the cartilaginous portion Movement of the
cartilaginous portion. ii. 12
Contrast medium in the ET Contrast medium in the ET. Dr-Ebtessam Nada
Eustachian tube function
a. Movement present, contrast medium seen in ET b. Movement absent, contrast medium present in ET c. Movement present, no contrast medium in the ET. B. Examination of Eustachian tube functions with intact TM:
1. Pneumatic Otoscopy (siegalization): movement of the TM with pneumatic Otoscopy indicates normal functioning tube. 2. Toynbee’s test:
with the pressure increased to +400
daPa, a closed nose swallowing is done, ET function is normal when you see a negative shift in TPP in pressure. A return to ambient pressure after that occurs indicating of normal function rather than only patency of the tube.
This return of ambient pressure indicates active opening of the tube by the action of the tensor veli palatini muscle and good stiffness of the tube structure that overcome the nasopharyngeal negative pressure.
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Eustachian tube function
After establishment of positive Toynbee (negative shift of the tympanogram) the patient is instructed to swallow with the nose open and observe the equalization of the induced negative pressure. Repeated open nose swallowing may be needed to equalize the negative pressure and the residual pressure is called residual negative pressure.
Tympanograms of Toynbee and Valsalva tests of Eustachian tube when the tympanic membrane is intact. R is the resting (starting) pressure then T is the negative shift attained by Toynbee maneuver then T1 and T2 after open nose swallowing. Positive shift attained by Valsalva is marked by V with equalization of pressure by swallowing resultin gin V1 and V2 tympanograms.
3. Valsalva test: pressurize to -400 daPa then hold nose and blow, and repeat tympanogram. A functioning results in positive shift in pressure. The total shift in pressure should be at least 15 - 20 daPa. Otoscopically bulging of the intact TM can be seen if the ET if functioning due to over pressure in the middle ear. 14
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4. Politzer test: Done in children who are unable to perform Valsalva. Similar to Valsalva but the nasopharynx is passively inflated by compressing one nostril into which the end of a rubber tube attached to an air bag has been inserted while compressing the opposite nostril by finger pressure. Compressed air can be used instead of Politzer’s bag. The subject is asked to swallow or to elevate the soft palate by repeating the letter "k." uncomfortable procedure.
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5. Sonotubometry: Principle: holding a tuning fork in front of the nostril, the sound is heard louder when the subject swallow as a wellfunctioning ET opens during swallowing results in more sound enters through the ET into the middle ear. History:
A. First:
Low frequency sound was used.
Test sounds were delivered through a rubber tube into
the nasal cavity (the length of the tube affects the response because of resonance).
Adjustment of the tube length was made according the
frequency of the sound used (wavelength).
The microphone in placed in a 38-mm thick wooden box
(risk of picking up unwanted noise).
B. Then:
A signal with a filter set of center frequency 200 Hz and
3.7dB bandwidth is used.
The microphone is tightly attached to the ear and speaker
is hermetically sealed to the nostril.
As swallowing produce sounds in the range of 100 to
2000 Hz which interferes with the test sounds; frequencies in the range of 6-8 kHz were more suitably used.
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Procedure:
A sound source generating a continuous sound of 6, 7, or
8 kHz is inserted and fixed tightly in the nostril of the patient.
A microphone contained within a circumaural ear muff is
placed in the ipsilateral ear canal.
The sound in the external ear canal is picked up by a
calibrated condenser microphone connected to a pre-amplifier to a sound level recorder.
The patient is asked to swallow water while sound signal
in the external ear is recorded.
Head should stay standstill and mouth closed.
Increase of the sound level by 5 dB suddenly indicates
opening of the tube.
Advantage: evaluate the Eustachian tube function with
or without an intact tympanic membrane under physiologic conditions.
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6. Catheterization Eustachian Tube Catheterization: A curved metal cannula is introduced trans-nasally, it can be done blindly, with the help of a nasopharyngoscope, or transorally with a 90° telescope.
Procedure: • Nose is anaesthetized. Pass the catheter along the floor of the nose until it touches the posterior wall of the nasopharynx then rotate it 90° medially and pull it forward until it impinges on the posterior free part of the nasal septum.
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• Then rotate the catheter 180° laterally, so that its tip lies at the nasopharyngeal opening of the Eustachian tube. • A Politzer bag is attached to the outer end of the catheter, and an auscultation tube with 2 ear tips is used with one tip in the patient's ear and the other in the examiner's ear. Air pushed by the Politzer bag is heard by the examiner as it passes through the catheter into the Eustachian tube and then into the middle ear. Lateral bulge of the TM is seen by Otoscopy. Results:
Successful transferring of applied positive pressure from
the proximal end of the cannula into the middle ear suggests tubal patency.
Normal blowing sounds mean a patent Eustachian tube
and bubbling indicates middle ear fluid.
Whistling suggests partial Eustachian tube obstruction.
Absence of sounds indicates complete obstruction or
failed catheterization.
Complications: Injury to the tube opening. Bleeding per nose. Spread of infection from the nose and nasopharynx to the middle ear. If TM has an atrophic area, rupture can occur.
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7. Pressure chamber technique: Middle ear pressure is measured indirectly by the response to pressure changes in a pressure chamber. Decompression of the chamber creates relative positive pressure in the middle ear, while chamber compression results in relative negative pressure in the middle ear. The resting middle-ear pressure is obtained from the initial tympanogram. Then the chamber pressure is lowered to 100 mm H2O relative to ambient pressure and a second tympanogram is obtained, verifying the relative overpressure in the middle ear. After this deglutition of the subject, a tympanogram is recorded to determine middle-ear pressure. The same procedure is repeated with 100 mm H2O relative overpressure in the chamber to assess the subject’s ability to actively equilibrate relative underpressure in the middle ear.
8. 9-steps Inflation deflation test:
Resting tympanogram is recorded.
Positive pressure of +200 mmH2O is applied in the
external canal. The patient is instructed to swallow to equalize the pressure.
Relieve the positive pressure in the external canal
(relative negativity) thus an outward movement of the TM occurs. Tympanogram is performed.
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Instruct the patient to swallow to equilibrate the negative
middle ear pressure. Successful equilibrium indicates air flow from the nasopharynx to the middle ear.
Then tympanometry is done to diagnose the extent of
equilibrium.
The next step is to induce negative pressure in the
external canal of -200 mmH2O, a lateral TM deflection occurs with subsequent decrease in middle ear pressure. Then the patient is instructed to swallow to equilibrate negative pressure.
Increase external canal pressure to normal (relative
positivity) with inward movement of the TM and positive middle ear pressure.
Swallow
to
reduce
this overpressure
and a final
tympanogram is recorded.
If the patient passed some or all of the steps tube
functions are considered normal.
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Tube-tympano-aero-dynamicgraphy: simultaneous
9. recording
of the
pressure
in the
external
canal
and the
nasopharyngeal cavity using a pressure transducer during Valsalva maneuver.
10.Tympanometry. Advantages: It is an objective way to determine the magnitude of negative middle ear pressure. Disadvantages: o A high negative middle ear resting pressure or presence of middle ear effusion is indicative of tube obstruction. However, no way to know whether obstruction of the tube is functional or mechanical or both. o The value of negative middle ear pressure as an abnormality is an important decision: Normal hearing can be obtains with high negative pressure levels.
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Eustachian tube function
Tinnitus, vertigo, otalgia can be found with modest levels of negative ear pressures. Middle ear pressure can be variable according to time of the day, season of the year or presence of upper respiratory tract infection. Presence of atelectasis or adhesions can obscure the actual pressure in the middle ear. A single point measurement cannot give an actual idea about the function of the tube.
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