Biomedical Engineering Reference
In-Depth Information
FIGURE 6-19
The
BAHA BP100
osseointegrated
hearing device.
(Courtesy of
Cochlear Ltd.)
FIGURE 6-20
Installation of
a BAHA
osseointegrated
hearing device.
(a) External view.
(b) Cross section
through the ear
showing attachment
method.
The principle of bone conduction amplification is that the external sound process-
ing device converts auditory signals into mechanical vibratory signals and conveys them
through the abutment and the BAHA implant into the mastoid bone, as shown in Fig-
ure 6-20. There is no airborne sound transmission, but the vibrations in the skull are con-
veyed directly to the inner ear where the hair cells are deflected by the normal physiological
mechanism (Finn and LoPresti, 2003).
This process bypasses both the outer and middle ear and is therefore ideal in cases
of conductive hearing loss. In addition, because of the efficiency of the device and the
available gain it is also useful in cases where some sensorineural hearing loss exists.
In cases of single-sided deafness (SSD), patients find that localization of the sound
source is impossible and discrimination is impaired. In these cases the BAHA device
is worn on the deaf side, and the sound seamlessly transfers to the other ear via bone
conduction, thus eliminating head-shadow problems (Flynn, 2007).
Figure 6-21 shows a simplified schematic diagram of the process. Sound picked up by
the microphone is amplified and processed to restore the appropriate spectral response for
the patient. This electrical signal then drives an electromagnetic actuator similar to a voice
coil that introduces vibrations into the mastoid bone through the titanium implant. It is
interesting to note that because the BAHA device is suspended from the titanium abutment
