Implantable Hearing Devices now available at Changi General Hospital

Most people with hearing loss can benefit from the use of hearing aids amplification. With the introduction of digital
technology and advanced signal processing the outcome of hearing aid rehabilitation has improved significantly over the years. In order to benefit from hearing aid amplification, the impaired ears must have some residual hearing to process the amplified sound. As a result, for patients with severe to profound hearing impairment hearing aids may become inadequate. Patients with single-sided deafness and those with chronic ear infections may also find little benefit from the use of conventional hearing aids. In view of the increasing needs for various advanced implantable hearing technologies, the ENT department in Changi General Hospital has introduced a full range of implantable hearing devices for adult patients.

1. Cochlear Implant: Hearing solution for severe to profound hearing loss.
For severe to profound hearing impaired individuals, hearing aids are of limited benefit as the cochlea is unable to process sound. A cochlear implant bypasses the damaged part of the ear and stimulates the hearing nerve directly. Cochlear implant systems convert everyday sounds into coded electrical pulses and stimulate the hearing nerve. The brain then interprets them as sound. Hearing through a cochlear implant is different from normal hearing and takes time to learn and relearn. However, with the advancement in implant technology many people with severe to profound hearing loss can once again have the ability not only to understand environmental sounds, but also to enjoy a conversation and participate in daily activities.

The cochlear implant system consists of an external speech processor that sits behind the ear and a second portion that is surgically placed under the skin.

How a cochlear implants works:

1. The microphone in the external speech processor picks upsounds from the environment.

2. The speech processor analyses the sound and converts it to digital signal.

3. The digital signals are sent to the coil and transmitted across the skin to the implant.

4. The internal implant in turn sends the signal to the electrodes, which stimulate the hearing nerve directly bypassing the damaged cochlea.

5. The brain recognises these signals as sound.

Adults with acquired bilateral severe to profound deafness who have little or no benefit from high power digital hearing aids are suitable candidates for cochlear implant as speech and language have already been developed. Better outcomes are achieved for patients who have shorter periods of hearing loss and who use hearing aids early.

2. Hybrid Cochlear Implant: Hearing solution for high frequency profound hearing loss.
Patients with mild to moderate low frequency (1 KHz and below) hearing loss and profound loss in the high frequency often complain of hearing difficulty even with hearing aids on. With only low frequency sound information being available alone, speech understanding is undermined. Currently, this group of ‘less profound’ hearing loss patients can be considered for cochlear implant. A new cochlear implant technology combining electrical stimulation (cochlear implant), and acoustic amplification (hearing aid amplification) has been developed
for this group of patients. This so called ‘hybrid’ implant system uses a shorter and more flexible electrode and allows electric stimulation of the basal cochlea for high frequency information, without damaging apical cochlear structures that transmit low frequency acoustic information.

Patients with potential useful low frequency hearing loss but significant losses in the mid to high frequencies can now benefit from both cochlear implant and digital hearing aid technologies without damaging the residual hearing.

3. BAHA (Bone Anchored Hearing Aid): Hearing solution for those with conductive/ mixed or single-sided hearing loss.
Sound can reach the inner ear through two paths. Firstly by air conduction via the ear canal and middle ear to the inner ear. Secondly by bone conduction where vibration bypass the outer and middle ear and conduct to the inner ear directly. BAHA system uses a process called direct bone conduction. A small titanium implant is placed in the bone behind the ear where it osseointegrates with living bone. This implant procedure is performed in a single stage in adults. Once osseointegration has taken place, a sound processor is clipped on. Sound is picked up by the external processor and is conducted directly
through the bone to the inner ear.

For patients with single-sided hearing loss, the BAHA system is placed on the deaf side and the device picks up sound and conducts it to the working cochlea of the good ear. This allows patients with single-sided hearing loss to hear sound from both sides where previously he can only hear it on one side. Recent studies confirm the efficacy of the BAHA in adults with single-sided deafness for recognition of speech in noise and improvement in directionality of sound. Since the BAHA system does not have any component in the ear canal, for those with recurrent ear infections it can leave the ear canal open which allows the ear to dry out and reduce the further incidence of recurrent ear infections while still
providing amplification.

4. Middle-Ear Implant (Vibrant Soundbridge): Hearing solution for adults with mild to severe sensorineural hearing loss, mild to moderate conductive and mixed hearing loss.
The Vibrant Soundbridge consists of an external audio processor and an implanted portion. The externally worn audio processor contains the battery, a microphone and a high performance digital signal processor. The audio processor picks up sounds and transfers the digitised signals to the implant. The implant unit consists of a hermetically sealed implanted coil, a conductor link and Floating Mass Transducer (FMT). The FMT is attached to one of the ossicles with a titanium clip. The Vibrant Soundbridge produces vibration, not sound. To compensate
for the loss in sensitivity of the impaired inner ear, the vibrations on the ossicles are amplified the FMT, which enhance the signal to the cochlea. The Vibrant Soundbridge was initially designed for adults with mild to severe sensorineural hearing loss in both ears. With the new development of the alternate surgical position within the middle ear of the implant mechanical drivers, the Vibrant Soundbridge can now be used for the treatment of conductive and mixed hearing losses. This development has allowed the FMT to be placed on any suitable vibratory structure in the middle ear including oval window, round window and in conjunction with partial
or total ossicular prostheses or on the head of the stapes. Patients with mixed hearing loss can now be considered for both BAHA system and middle ear implant system.