Within the relatively small structure of the ears, nose, and throat are several very complex mechanisms that allow us not only to make sound but also to hear, to keep our balance, to smell, to breathe in and filter air, and to swallow food and water. These mechanisms are interrelated and generally carry out their functions without our being aware of the processes at work.

How hearing works

The ear is divided into three parts: the external ear, the middle ear, and the inner ear. The primary function of the outer ear or pinna is to collect and carry sounds (which are essentially vibrations) to the middle ear. Sound waves travel through the outer ear canal and strike the eardrum, which vibrates like a drum and converts the waves to mechanical energy.

This energy resonates to the middle ear, where tiny bones vibrate to the rhythm of the eardrum, amplify the sound, and pass the sound waves on to the inner ear.

The inner ear (or cochlea) is fluid-filled and lined with tiny hairs. Vibrating sound waves cause ripples in the fluid, which then bends the tiny hairs. This process converts the sound into nerve impulses, which then travel along a network of nerve cells (the auditory or eighth cranial nerve) to the brain, which perceives these impulses as sound.

We receive sound in two ways by air conduction via the ear canal, eardrum and ossicles and by bone conduction where the sound is transmitted directly through the jaw and skull bone bypassing the outer and middle ears.

What is a BAHA?

The Bone Anchored Hearing Aid system is surgically implanted and allows sound to be conducted through the bone rather than via the middle ear - a process known as direct bone conduction. A small titanium implant is implanted into the skull behind the ear where it osseointegrates with the living bone. An abutment is attached to the implant and a sound processor is clipped on. The sound processor can be worn or taken off at any time. The sound quality is greatly improved compared to traditional bone conducting hearing aids.

How does it work?

The system works by enhancing natural bone transmission as a pathway for sound to travel to the inner ear, bypassing the external auditory canal and middle ear. The titanium implant over time naturally integrates with the skull bone. For hearing, the sound processor transmits sound vibrations through the external abutment to the titanium implant. The vibrating implant sets up vibrations within the skull and inner ear that finally stimulate the nerve fibers of the inner ear, allowing hearing.

In most cases, hearing impaired people will be fitted with air conduction devices. These are placed inside the ear canal or behind the ear. However, some hearing impaired people are unable to benefit from this type of device. They may have a congenital deformity wherein there is no functioning ear canal in which the hearing aids can be fitted or may have a chronic ear infection in the middle or the outer ear that is made worse when a hearing aid is worn. Also patients with inner ear insufficiency on one side and a conductive deafness on the other side where there is a potential risk of making the only functioning cochlea unusable by ear surgery will benefit from the implant.

BAHA for children

Children born with malformations of the outer and middle ear can still have perfect inner ear function.

The author is a senior consultant in ENT, Apollo Hospitals and can be contacted at 9900236819 or email: drkumaresh@drkumaresh.com