Lending a ear

Most people hesitate to wear a hearing aid. Dr. K.K. RAMALINGAM and Dr. RAVI RAMALINGAM remove misconceptions and explain why it is useful.

The problems of deafness are deeper and more complex, if not more important, than those of blindness, a bigger misfortune. For it means the loss of the most vital stimulus.... the sound of the voice that brings language, sets thoughts astir and keeps us in the intellectual company of man.

Helen Keller

NOT only is hearing important for speech development, the quality of developed speech is constantly monitored by proper hearing. If a person becomes deaf, he is likely to lose speech too.

Humans can hear sounds of 20-2000 Hz, though the speech frequency is only from 500-4000 Hz. Sound travels as waves and reaches the tympanic membrane through the ear canal. When the tympanic membrane vibrates the three ossicles - malleus, incus and stapes - also vibrate. The malleus is fixed to the tympanic membrane and the stapes separates the middle ear from the inner ear. Sound energy travelling in the air travels through the ear canal and through the tympanic membrane and ossicles in the middle ear. When the stapes bone vibrates it sets up corresponding vibrations of the fluid in the inner ear.

The peripheral end organ of hearing is situated in the inner ear and is stimulated by the vibrations of the fluid. These signals are picked up by the eighth cranial nerve or the acoustic nerve which transmits the impulses to the hearing centre in the brain where it is decoded.

Thus, the transmission of sound in the external and middle ear are mechanical whereas in the inner ear and beyond it is the nerve of hearing. Pathologic conditions of the external and middle ear causes conductive deafness. If in the inner ear or eighth cranial nerve, it causes nerve deafness or sensorineural deafness. Men, women and children of all age readily wear spectacles for their visual defects. But many hesitate to use a hearing aid.

Most hearing aids are air conduction aids. In this, the amplified sound is transmitted via the ear canal to the tympanic membrane. In bone conduction hearing aids, there is a bone vibrator which snugly fits on to the mastoid bone and directly stimulates the cochlea. These aids are specially useful to persons who have discharge in the ears, inflamed external ears, stenosed or absent ear canals where the inserts cannot be fitted. Amplification and acoustic gain is less. This is suitable for mild to moderate conductive deafness only.

Air conduction hearing aids are of different types. The body- level aid has a microphone, amplifier and battery in one case which is worn at chest level. The receiver alone is at ear level. It allows high degree of amplification with minimal feedback, and is mostly the severely deaf or children with severe or profound congenital deafness.

In the contra lateral routing of signals (CROS), a microphone is fitted to the side of the defective ear and the sound picked up is passed to the receiver placed in the better ear. This is useful to persons with one ear totally impaired and helps in sound localisation coming from the side of the deaf ear.

Those are programmable and digital hearing aids to in the former hearing health care professional programmes or adjusts certain sound features in the aid using the state of at programmer or computer. The sound features are designed to more accurately fitting the individual needs and give the patient distinct, high quality amplification. They can be readjusted or reprogrammed if necessary.

The digital aids offer all the advantage of digital technology. You hear loud and soft sounds, high and low tones practically at the level of a person with normal hearing. Added to this comes excellent speech intelligibility in noise. This means that low frequency noise, such as in a car or aircraft, is reduced and the clarity of speech enhanced to a pleasant level.

Cochlear Implants, which are still in the development phase, are electronic devices which convert sound signals into electrical impulses which then directly stimulate the cochlear nerve. Even if the nerve is non-functional the electrode can be placed on the brain stem. Thus cochlear implants replace the non functional transducive system of hair cells of the cochlea.

It is a common misconception that cochlear implant is a new type of hearing aid implanted inside. However, the patient who undergoes cochlear implant surgery has to wear the speech processor instead of a hearing aid. Post lingual adults benefit by cochlear implants. Careful selection of cases and extensive rehabilitation are necessary.

Vibratory ossicular replacement prosthesis or vibrant sound bridge system is the latest development in hearing aids. The hearing aid is fixed onto the incus bone of the middle ear. This is suitable for mild to moderate hearing loss. Only about 100 of these operations have been done all over the world.

Another type is the total implantable hearing aid which is implanted over the mastoid bone. Nothing will be visible outside. This consists of a microphone implanted deep the ear canal, under the skin near the ear drum.

An electro-mechanical transducer directly moves the ossicles in the middle ear and the main module for electronic amplification is placed in a recess behind the ear. There is no need for a ear mould, no distortion and the person can take a shower or swim with the hearing aid.

The tiny battery which forms the power source is contained with the main module. This battery is recharged from outside by wireless power transmission. The person has to wear a device like a headphone for about two hours every two to three days.

During charging, the device is fully functional and so it can be charged while watching TV or riding in a car. This device offers different settings to suit different listening situation. This type of hearing aid system is in the development stage and holds promise for the future.

Hearing aids are designed to give the best reception for the speech frequencies and therefore the range of amplification is usually from 250 to 4000 Hz. Since most of the sensorineural hearing loss affects the higher frequencies more than the lower frequencies, reduced amplification in the lower frequencies helps prevent masking of the higher frequencies by the amplified low tones. The frequency response of the aids can be adjusted to the patient's requirements. In many hearing aids there is a tone control which can be used to increase slightly, gain in the higher frequencies which can help understanding speech.

Persons with conductive type of deafness get best results by wearing hearing aids. Of course, surgically correctable conditions can be operated to improve the hearing to avoid use of hearing aids.

The problems of patients with sensorineural hearing loss who start to wear hearing aids is that a powerful amplification may distort sound. In the classical high tone hearing loss the consonant sounds which carry most of the meaning of speech are not as clean as vowel sounds which act as carriers for the consonants.

An otologist or E.N.T. surgeon must always be consulted on ear care. Never buy hearing aids across the counter. The patient may have a treatable condition, which may be cured and hearing restored without the need for an aid.

Wax or fungus may block the ear and will have to be cleaned before fixing the aid. Otherwise the sound transmission will not be good. The ear canal skin may have a tendency for inflammation and this must be treated. Audiogram will assess quantitative and qualitative nature of hearing in both ears.

Generally, the hearing aid is advised to be worn in the better of the two ears. Also the hearing aid is the treatment of choice for only hearing ear or if there is any medical contra indications for operation mellitus like local inflammation, systemic blood pressure and diabetes diabetes which are not controlled. The possibility of noise induced hearing loss due to over amplification by the hearing aid should also kept in mind.

Selection of suitable hearing aid is important depending on the degree and type of hearing loss for the person.

Accurate fitting is important by making a custom mould made of soft silicon material so that it does not injure the ear canal and the patient feels comfortable. It is very important that the mould fits snugly in the ear.

The patient must be given full instruction of using the hearing aid: maintenance, care of the instrument, changing the batteries and periodic check up of the instrument. The patient should be told that it takes time and perseverance to get the best use of hearing aid. The patient usually gets used to the problem of background noise in course of time.

The person should make it a habit to switch off the instrument before taking it from the ear.

Remember to keep your hearing aid dry; Never subject it to high temperatures. Avoid dropping the instrument. Store your aid out of reach of pets or youngsters. Remove your aid before applying hair spray. Do not use solvent to clean your aid. Do not lubricate any part of your hearing aid. Never attempt to repair your own hearing aid. Refer all questions or service matters to your dispenser and have your aid checked frequently.

Ten myths and 10 facts:

Myth: Only a few people have a hearing problem and neither I nor those close to me are deaf.

Fact: You or someone close to you has some degree of hearing impairment.

In fact, it has been estimated that 100 million Indians suffer from some form of hearing problem.

Myth: If my hearing decreased, I would certainly know.

Fact: Not necessarily. Often hearing impairment develops slowly and subtly. Our own built-in defenses may make it difficult for us to determine whether we do or do not have a hearing impairment. A simple hearing test would determine if hearing impairment exists.

Myth: Hearing aids will not restore impaired hearing to normal.

Fact: Hearing aids are designed to aid a person's hearing. Hearing aids cannot restore human hearing nor can they retard the progression of deafness. They are only part of hearing rehabilitation and may need to be supplemented by hearing training.

Myth: Will hearing aids help in the presence of distracting background noise?

Fact: Understanding, especially in a noisy environment, will vary depending on each person's hearing loss. Overall benefit may depend on the severity of hearing loss, accuracy of the patient evaluation, proper hearing aid, frequency of use and auditory rehabilitation.

Myth: When someone has decreased hearing, that just means that sounds are not loud enough.

Fact: That is only partially true. The person may also have trouble hearing in crowds or in group conversations. Perhaps they hear sounds but don't always understand what's being said. Spoken words may seem to be mumbled or words just run together.

Myth: Hearing aids are large and unsightly and can carry stigma. Most people therefore don't want to wear them.

Fact: Most people are not aware of the latest technological advances in hearing aids that have made most old-fashioned hearing aids obsolete. Now "inside-the-ear hearing aids" exist and these aids are amazingly small and discreet.

Myth: Wearing a hearing aid is a sign indicating you are getting old.

Fact: Although hearing impairments are common in older adults, many middle age and younger people affected as well. There are many other factors which affect hearing other than just age. Do not forget, a hearing loss is more noticeable than a hearing aid.

Myth: I have heard that may type of hearing loss can't be helped.

Fact: In most cases, where hearing loss is due to nerve problem, it be can helped through amplification. Now, patients with nerve deafness are no more helpless.

Myth: Good hearing aids are very expensive.

Fact: Even best hearing aids available are within the reach of most people. A hearing aid could be best investment you can make.

Myth: Hearing tests are expensive and inconvenient.

Fact: Routine hearing tests usually cost less than Rs. 200 at most E.N.T. hospitals.

The writers are with the KKR ENT Hospital and Research Institute, Chennai.

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