HEALTHWATCH
All in the ear
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The Eustachian tube is important for the proper functioning of the ear. Prof. K. K. RAMALINGAM, Dr. RAVI RAMALINGAM, and Dr. T. M. SREENIVASA MURTHY explain its functions and problems.
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THE Eustachian (named after Eustachius) tube is a tubular structure connecting the middle ear and the upper part of the pharynx (Nasopharynx). It plays an important role in the proper functioning of the ear.
In infants and young children, the tube is wider, straighter and shorter than in adults. As the child grows, it gradually assumes the narrower, oblique and longer course.
Structure
The tube is partly bony and partly cartilaginous. The lateral tympanic part, which is bony, is always open. The medial pharyngeal part is an incomplete hook-like cartilage. The rest of the pharyngeal part is covered by muscle and soft tube.
Two muscles — the tensor and levator palatine muscles — help the tube open and close. Normally this is closed and it opens only during chewing, swallowing, crying and yawning. The tube's lumen is narrow and lined by respiratory mucous membrane or cilia.
The cilia beat towards the pharynx and help move any mucous particles or secretions from the middle ear to the pharynx. Secretions and mucous are normally prevented from aspirating into the middle ear because the tube is kept closed. When the tube opens, air either enters or exits the middle ear.
Functions
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Workings of the inner ear are quite complex.
The air pressure on either side of the eardrum is normally kept equal for proper functioning of the middle ear structures, namely the malleus, incus and stapes bones.
As we climb, the atmospheric pressure is less compared to the middle ear pressure. Excess air from middle ear finds its way into the pharynx passively by opening the Eustachian tube. During descent, the reverse happens. So more air has to enter the middle ear to equalise the pressure. This can happen only when the muscles contract actively to open the tube.
The middle ear and mastoid air cell system normally contain air. If the tube is blocked, air is absorbed from the middle ear leading to exudation of fluid into the middle ear, due to negative pressure created by absorption of the air and non-replacement of air because the tube is kept closed.
Problems in children
In infants, because the tube is shorter, straighter and wider, there are more chances of milk or secretion from the pharynx aspirating into the ear. This causes frequent ear infections, pain and, in severe cases, perforation of the eardrum and discharge from the ear.
If the tube's lining swells due to infection or allergy it will close easily. Also in children the adenoids tend to block the tube's pharyngeal end. Whenever the tube is blocked, the air in the ear is absorbed leading to exudation of fluid into the middle ear. This may be serous or, in chronic cases, thick, mucoid and glue-like.
When this happens, the child may suffer hearing loss. If the condition does not respond to medical treatment, incision of the eardrum (Myringotomy), removal of the fluid by suction and insertion of a drainage tube (Grommet tube) is required.
In advanced countries, more than 90 per cent of children below five years of age have Myringotomy and Grommet tube insertion. Some children need more than one operation.
If left untreated, it can lead to permanent hearing problem when treatment will be much less effective, if at all. In long standing cases, it may cause irreversible changes in the eardrum, destruction of the underlying bones in the middle ear and severe grade of hearing loss.
Obstructions
In certain situations, the tube may be anatomically patent but may not function properly physiologically. This happens in children with cleft palate.
In these cases, the muscles that open the tube cannot contract effectively. So most children with cleft palate suffer from frequent otitis media, ear discharge and deafness. Even after successful operations for cleft palate, these muscles do not perform well and so the problems persist to a great deal.
Mechanical obstructions may be intra luminal (allergic and infected swelling of the tube's mucosal lining) or extra luminal (tumours pressing on the tube or adenoids).
Other causes of dysfunction may be nasal obstruction caused by polyps, deflected nasal septum, sinusitis, trauma to the tube or to the pharyngeal opening which may occur during adenoidectomy or after surgery for removal of tumours in the region.
Tests for dysfunction
Valsalva manoeuvre: Most people can insufflate their middle ears by closing the nose and mouth and increasing the intra-pharyngeal pressure. This is called Valsalva manoeuvre. If performed successfully, it indicates that the Eustachian tube is anatomically patent. But it does not indicate whether the tube is functioning normally.
Eustachian tube catheterisation: Using a Eustachian catheter, air can be blown through the pharyngeal opening.
Politzerisation: Using the nozzle of the Politzer Bag through the nostril and asking the patient to drink water or say K, K, K, sudden pressure on the bag will blow air into the closed pharynx. Air will pass through the Eustachian tube into the middle ear if tube is patent.
Impedance Audiometer: This measures the air pressure and the compliance in the middle ear and helps evaluate the function of the Eustachian tube.
In air
Air travel is best avoided during an attack of cold because the tube may not function properly during an attack of cold.
During the descent of the aeroplane, the person with poor Eustachian tube function may experience severe pain and may go in for Baro-trauma resulting in bleeding into the middle ear.
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While feeding infants, the head should always be kept higher.
Burp the child immediately after a feed.
Do not blow the nose violently during a cold.
All children should have regular ENT check up and periodical hearing tests.
Children with glue ear need to undergo Myringotomy and grommet insertion.
Avoid flying when you have a cold. If unavoidable, use antihistamines, topical and systemic decongestants and perform Valsalva manoeuvre.
Surgery for discharge in the ear is successful when the Eustachian tube is functioning.
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