For people with hearing loss, there are many amplification options available. Temple’s Dr. Maria Pomponio describes one particular hearing system, the Bone Anchored Hearing System (BAHS), previously known as the Bone Anchored Hearing Aid (BAHA) that can help people with certain more significant types of hearing loss.
How Do We Hear?
In order to better understand what a Bone Anchored Hearing System (BAHS) is, it is important to first understand how we hear. Traditionally, sound waves from the environment enter the outer ear and travel down the ear canal to reach the eardrum. When sound waves make contact with the eardrum, the eardrum vibrates. This causes three small bones (the malleus, the incus, and the stapes) in the middle ear to vibrate, since the eardrum connects to these bones. The vibrations from these bones travel to the cochlea, a bony part of the inner ear that is filled with fluid and hair cells. The vibrations cause the fluid in the cochlea to move, which in turn causes the hair cells to move. When the hair cells move, an electrical signal is created and carried up to the brain by the auditory nerve. The brain makes sense of these signals so we can understand and identify them as different sounds.
When an individual has difficulty receiving sound from the outer ear and/or transmitting sound through the middle ear, he or she may have a conductive hearing loss. When the cochlea or the auditory nerve is damaged, an individual may have a sensorineural hearing loss. Conductive hearing losses may be correctable, whereas sensorineural hearing losses are often permanent. If an individual has a conductive hearing loss and a sensorineural hearing loss, he or she has what is called a mixed hearing loss.
When Is a BAHS Recommended?
Individuals with hearing loss often hear about a variety of options to help improve their hearing. People with conductive hearing losses may be treated with a hearing aid. A hearing aid picks up sound and transmits it through the outer and middle ear to the cochlea of the inner ear before the signal is sent to the brain. When used in cases of conductive hearing loss, hearing aids must be powerful enough to sufficiently amplify sound to overcome the cause of the conductive hearing loss. When appropriately amplified, we can ensure that the sound will arrive at the cochlea at a useful volume. For individuals with a significant conductive component to their hearing loss, a hearing aid may not be powerful enough to effectively transmit this signal to the cochlea (and ultimately, the brain). A BAHS may be recommended instead, as it functions by stimulating the cochlea directly. As a result of this direct stimulation, less power is needed from the device. This may make the BAHS preferable over hearing aids in some cases.
Additionally, hearing aids are not feasible options for all individuals with conductive hearing loss. A BAHS is sometimes recommended instead of a hearing aid when a person cannot use a traditional hearing aid due to a malformation in the external ear or ear canal (e.g., certain medical conditions such as microtia or atresia). Additionally, a BAHS may be more practical than a hearing aid for someone who has chronic drainage from their ears, which may prevent hearing aid use or making hearing aid use difficult.
Individuals with mixed hearing loss may be candidates for a BAHS depending on the degree of the conductive hearing loss, and if the damage to the cochlea (the sensorineural component of the hearing loss) is not too significant. Individuals with a significant sensorineural hearing loss in both ears have difficulty hearing even when sounds reach the cochlea. These individuals often try to use hearing aids as a means of improving their hearing. When hearing aids are no longer helpful enough for these individuals, a cochlear implant may be recommended. A BAHS would not be recommended for individuals with bilateral sensorineural hearing loss because neither cochlea is working well enough for the BAHS to be useful. For individuals who are deaf in one ear but have essentially normal hearing in the other ear, a BAHS may be useful as it will rely on the well-functioning cochlea to operate efficiently.
In Summary: A BAHS is typically recommended as an option to help individuals with conductive or mixed hearing losses, as well as individuals who are deaf in one ear only (typically referred to as “single sided deafness”, or SSD).
How Does a Bone Anchored Hearing System Work?
Now that we understand how we hear, the different types of hearing loss, and the types of hearing losses in which use of a BAHS is appropriate, we can explore how a BAHS works. A BAHS is comprised of three parts: a sound processor, an abutment, and a titanium implant.
The photo depicts (1) the external sound processor, which vibrates when sound is received. The external sound processor connects to (2) an abutment. The vibrations from the sound processor are transmitted to the abutment, which then transmits the vibrations to (3) the internal titanium fixture.
This titanium device is surgically implanted into the skull bone behind the recipient’s ear. When the titanium implant vibrates, the entire skull vibrates (remember: the titanium implant is fused to the skull bone!). This causes direct stimulation of each (right and left) cochlea, where the hair cells convert the vibrations into an electrical signal to be sent on to the auditory nerve and ultimately, the brain. One currently available bone anchored system allows (1) the external sound processor to connect via (2) a magnet to (3) the internal titanium fixture.
Vibrations from the sound processor are sent through an external magnet to an internal magnet, which is connected to the titanium implant. Once the vibrations reach the titanium implant, the bones of the skull vibrate and, as a result, each cochlea is stimulated.
What Should I Do if I Think I am a Candidate for a BAHS?
If you think you might be a candidate for a BAHS, or any other device mentioned above, the first step is to schedule an appointment with one of our otologists. An Otologist is an Ear, Nose, and Throat (ENT) physician who specializes in conditions that affect the ear. The otologist will examine you and then send you to an audiologist for a regular hearing test. If the hearing test reveals a conductive or mixed hearing loss that meets specific candidacy criteria, or reveals deafness in one ear only, the audiologist and otologist may recommend more testing to determine if you would benefit from a BAHS. If you are a candidate for a BAHS, the otologist will determine if you are healthy enough to have the surgery. Several appointments with the audiologist will be necessary after surgery to program and adjust the device to your liking.