Hearing aid is a device that improves hearing. It enables deaf people to understand speech, use the telephone and enjoy music.
In 1876 Alexander Graham Bell the noted American scientist while experimenting to develop a hearing aid to help deaf children, invented the telephone. The principle employed formed the model for electric hearing aid.
COMPONENTS OF HEARING AIDS
Electronic hearing aids are essentially small telephone or public address system. These consist of a microphone, an amplifier and a receiver. The ‘MICROPHONE’ transforms the acoustic signal (ie the sound of speech, music etc) to an electrical current (signal).
The ‘AMPLIFIER’ increases the power of the signal.
The ‘RECEIVER’ converts the electrical impulses (signal) from the amplifier into sound energy.
Therefore the microphone picks up the sound, amplifier amplifies (increases) the sound and to some extent modifies the sound and finally the listener hears the sound through the receiver, fitted into the ear with the help of ear mould.
All these components require a power source, which is provided by batteries.
TYPES OF HEARING AIDS
- According to size and shape
- Body worm aid
- Behind the ear aid(BTE)
- In the ear aid (ITE)
- In the canal aid (ITC)
- Completely in the canal aid (CIC)
- Air condition aids and bone conduction aids
- According to technology
BODY WORN AIDS – The microphone, amplifier and batteries are incased in a small box, which is clipped with the pocket of shirt or with the vest. A length of wire connects the amplifier with the receiver, which in turn is attached to the ear with an ear mould.
BEHIND THE EAR (BTE) AIDS – These aids fit behind the pinna an are held in place by a hook shaped rigid tube fits over the pinnia. A soft polythene tube is connected to this rigid hook shaped tube and to the ear mould fitting into ear canal.
IN THE EAR AID (ITE) – This type of aid consists of a signal piece. The electronics is places inside a shell that fits in the patient’s ear canal. The shells are individually prepared according to the size a shape of the external ear canal of the patient.
IN THE CANAL AID (ITC) – protrude slightly from the ear canal.
COMPLETELY IN THE CANAL (CIC) AIDS are placed completely with in the ear canal, only a clear filament protrudes from the ear canal to help removal of the aid.
SPECTACLE AID – The electronics of the hearing aid is constructed inside the hollowed spectacle frame.
AIR CONDUCTION AIDS – Amplifies the sound and brings it directly to the ear canal by a ear mould. The sound reaches the ear drum after traveling through the air column in the external ear canal.
BONE CONDUCTION AIDS – These aids bring the amplified sound waves as vibrations directly to the bone behind the ear. The bone transmits the vibrations to the nerves of hearing (cochlea and auditory nerve)
ANALOG AIDS – This type of aid is already discusses in “components of hearing aid” section. This type of aid is widely used. These aids are less expensive, but has disadvantage of having internal noise and less efficient frequency response.
DIGITAL AIDS – it has bean a major break through in improving the quality of life for hearing impaired people. Now a days every one loves to hear digital sound for its superb quality and clarity and deaf people are no exception. Keeping these in mind various International Brands are presently available in the Indian market and are sold through authorised dispensing center. Preferred by Deaf people worldwide for its unmatched quality and unique feature like automatic noise reduction and automatic volume control makes the ultimate pleasure in listening. In this type of aid the electrical signals are further modified to digital signals coded by binary numbers (Computer Technology). This is a very advanced type of aid having little internal noise as compared to analog circuitry. Digital aids can be programmed according to the patients individual needs (similar to dispensing glasses for eye sight defect). Digital aids may be constructed having several frequency responses that the patient can select depending on his or her auditory environment by switching.
EAR MOULDS – Ear moulds convey sound from the receiver to the ear canal in air conduction aids. The ear moulds should the ideally prepared according to size and shape of the external ear canal of the user i.e. it should be custom made. These custom made moulds are comfortable to wear and avoids the annoying noise of acoustic feed back in loosely fitting ear moulds. The efficiency of the hearing aid can be improved by modifying the length of the ear mould canal, bore size or providing size in side vents.
SEELECTION OF HEARING AID Hearing aids are useful in both conductive and nerve deafness. As conductive deafness is treated by medicine and surgery, hearing aid is mostly used in nerve deafness. Selection if the Proper type of hearing aid is crucial because a wrongly selected aid will cause frustration and ultimately non compliance.
The correct type of hearing aid is selected after performing hearing test by Pure tone audiometry and speech audiometry. These tests measures the hearing loss in different frequencies, particularly 250, 500, 1000, 2000, 4000 Hertz (Hz) and the patients ability to hear and understand real time speech sound. A hearing aid having ‘gain’ (capacity to amplify the sound) and frequency response (ie the range of frequencies amplified by the aid) suitable to the hearing loss pattern as obtained in the audiommetry is selected. A digital hearing aid can be tailor made according to the patients hearing loss pattern.
Therefore it should be appreciated that hearing aid. Should be dispensed after all tests ad not be directly purchased from the market – like any other electronic commodity.
Counseling the patient is very important after fitting the hearing aid. A patient who has not been hearing sound for long forgets how sounds really should sound. Patient re-learns to ignore the unwanted back ground sounds and concentrate on the meaningful sounds only. The patient requires to learn once more the skills of listening and understanding the new sound material being presented to the war by the hearing aid.
If counseling is not done after fitting the hearing aid it may lead to non acceptance of the aid, particularly in the elderly. Counseling is done by audiologists.
PROBLEMS OF USING HEARING AIDS
- Annoying sound produced due to poor fitting of ear mould.
Remedy -> Custom made ear mould.
- Amplification of background noise and distortion of sound.
Remedy -> Counseling and rehabilitation.
- Pain in the ear – usually due to inflammation of the external ear.
Remedy -> see a doctor and treat.
- Uncomfortable, often painful loudness perceived by hearing aid user
(Seen in some nerve deafness cases – a phenomenon call recruitment)
Remedy -> Hearing aid installed with special facilities.
(Compression circuit, Peak clipping, Automatic Gain control, Automatic volume control etc.)
- Cosmetic unacceptability & fear of identified as hearing handicapped.
Remedy -> In the ear aids (ITE)
IEC & CIC aids.
These are very small size aids with smaller control switches. Elderly people with arthritic finger find it difficult to use. Behind the ear (BTE) aids are good alternatives. Pocket aids (Body worn aids) are fast loosing popularity due to its cumbersome size, presence of wire. But when high amplification is required body worn aids are used as in severely deaf patients, deaf a mute children.
TIPS TO HEARING AID USER
- Always buy a proper model & type of hearing aid after hearing tests as per advice of ENT specialist and care of audiologist.
- Pocket aids (body worn aids) are more resistive to physical shock, moisture etc. cheap and easy to maintain.
- Miniature aids (In the Canal, Completely un the canal aids) are difficult to manipulate for the elderly subjects.
- Servicing, repair and spares are available with the hearing aid providers (dispensors).
- It takes days to weeks to get adjusted to hearing aid. Do Not get frustrate and cotact – the audiologist for counseling.
- Always remove the hearing aid and switch it off , before taking a shower or going to bed etc.
- Use a custom made ear mould to avoid the annoying fee back noise. This will add some extra cost.
- Check and change the battery, whenever the performance of the aid deteriorates. Do not compensate for a week battery by increasing the volume of the aid – this distorts the sound. Contact the hearing aid provider if performances do not improve. Note that hearing aids consume batteries more than you will normally expect.
- Most of the hearing aids are provided with a facility to use with telephones. Always switch to the telephone mode while attending telephone calls. You hearing aid dispenser will show you this facility.
- If there is pain and discharge in the ear see ENT doctor immediately.