Physiology III - Bone Conduction

The middle ear overcomes the impedance mismatch between air and fluid by using two mechanisms: the tympanic membrane amplifies pressure by focusing sound onto the smaller oval window, and the ossicles increase mechanical force between the tympanic membrane and the oval window.

Air conduction sound transmission is the process by which sound waves travel from the outer ear to the inner ear through the air. This process involves the tympanic membrane, ossicles, and oval window.

The gain of sound pressure in the middle ear is approximately 20 dB at frequencies between 250 Hz and 500 Hz. This gain reaches a maximum of 25 dB around 1000 Hz and decreases by 6 dB per octave at higher frequencies.

Hearing aids are electronic devices that amplify sound to compensate for hearing loss.

Hearing aids capture sound with a microphone and then process and amplify it in different frequency channels. This allows them to be tailored to an individual's specific hearing loss.

Hearing aids are primarily used to compensate for sensorineural hearing loss, which affects the inner ear or auditory nerve.

Behind-the-ear (BTE) hearing aids sit behind the ear and connect to an earmold or earpiece inside the ear canal.

In-the-ear (ITE) hearing aids are custom-molded to fit directly into the ear canal or the ear's outer portion.

The amplification of low-frequency sounds due to the ear canal being closed, trapping vibrations within the ear canal. This creates a louder perception of low-frequency sounds.

The process of sound transmission through the bones of the skull directly to the inner ear, bypassing the outer and middle ear.

Transmitting sound vibrations directly through the skull, bypassing the outer and middle ear. They allow users to hear audio while staying aware of their surroundings.

The primary way sound reaches the inner ear, involving vibrations traveling through air from the outer ear to the eardrum.

A method of sound transmission through the cartilage in the external ear, generating audible sound with clarity comparable to AC and BC.

The medium involved in the transmission of vibrations for bone conduction, primarily through skull bones.

The medium involved in the transmission of vibrations for cartilage conduction, specifically the cartilage in the external ear.

Bone conduction (BC) is a process where sound vibrations are transmitted through the bones of the skull to the inner ear, bypassing the outer and middle ear.

BC hearing tests assess hearing by delivering sound vibrations directly to the skull bones, allowing audiologists to evaluate the function of the inner ear, even if the outer ear and middle ear are not working properly.

Percutaneous BC devices are implanted surgically, with a small part of the device placed under the skin and a larger part placed behind the ear. They are a more invasive option but offer more potential power.

Transcutaneous BC devices sit on the skin behind the ear, often using a magnet or suction to stay in place. They are less invasive than percutaneous devices, but may be less powerful.

Cartilage Conduction (CC) is a type of BC where sound vibrations are transmitted through the cartilage of the ear, providing a comfortable and discreet option for some individuals with hearing loss.

The ADHEAR is a non-surgical BC device that uses a no-pressure adhesive adapter, providing all-day comfort. It's a less invasive option but offers a more limited level of power.

The Bonebridge and Sentio are BC devices suitable for patients with BC thresholds below 45 dB in the 500 Hz to 4000 Hz frequency range.

The Osia is a BC device suitable for patients with BC thresholds below 55 dB in the 500 Hz to 3000 Hz frequency range.

The Ponto and BAHA are BC devices suitable for patients with an air-bone gap exceeding 30 dB in the 500 Hz to 3000 Hz frequency range, and BC thresholds below 65 dB in the 500 Hz to 4000 Hz frequency range.

The Pure Tone Average (PTA) for BC thresholds is calculated by averaging the BC thresholds at frequencies of 500 Hz, 1000 Hz, 2000 Hz, and 3000 Hz.

The occlusion effect refers to the amplification of low-frequency sounds caused by the ear canal being plugged, trapping vibrations inside. This makes those low-frequency sounds seem louder.

Bone conduction (BC) is the way sound travels through the bones of the skull, directly to the inner ear, bypassing the outer and middle ear.

Air conduction (AC) is the usual way sound reaches the inner ear, travelling through the air from the outer ear to the eardrum.

The occlusion effect can make it difficult to hear high-frequency sounds, resulting in a negative impact on hearing protection.

Behind-the-ear (BTE) hearing aids are placed behind the ear and connected to a mold inside the ear canal.

In-the-ear (ITE) hearing aids are custom-made to fit directly within the ear canal.

Sensorineural hearing loss affects the inner ear or the auditory nerve.

The occlusion effect is a common limitation of hearing protection devices, as it can make it difficult to communicate and creates safety concerns.

The air-bone gap (ABG) is the difference between air conduction and bone conduction hearing thresholds at specific frequencies, usually calculated across a range of frequencies. It helps determine the type and severity of hearing loss, and can indicate middle ear problems.

Percutaneous bone conduction devices are implanted directly into the bone behind the ear. They are used to deliver sound through the skull, bypassing the middle ear, to those with conductive or mixed hearing loss.

Transcutaneous bone conduction devices are external devices that transmit sound through the skull, bypassing the outer and middle ear. They are held in place by a headband or other external support.

Bone conduction hearing tests are used to assess the function of the inner ear independently from the outer and middle ear. They measure the ability to hear sound transmitted through the bones of the skull, providing information about the cochlea and auditory nerve.

Bone conduction devices are used to amplify sound by bypassing the outer and middle ear, delivering sound directly to the inner ear. These devices are used to help people with conductive hearing loss, mixed hearing loss, and single-sided deafness.

Candidacy criteria for bone conduction devices consider factors such as the type and degree of hearing loss, the patient's medical history, and their lifestyle. Assessing these criteria ensures that patients are suitable candidates for this type of device.

The occlusion effect can be a significant factor in reducing the comfort and acceptability of hearing protection. When the ear canal is blocked, the listener's own voice sounds muffled or distorted, which can lead to discomfort and a desire to remove the device or wear it intermittently. This can ultimately hinder the effectiveness of hearing protection in preventing noise-induced hearing loss.

The occlusion effect can also impact in-ear hearing aids, resulting in an altered perception of sound. Users may experience their voices sounding hollow or echo-like, a general reduction in the overall sound volume, and sometimes even distorted sound perception. These side effects can discourage the use of hearing aids, hindering their potential benefits for the user.

Bone conduction (BC) refers to the transmission of sound vibrations through the bones of the skull directly to the inner ear. This process bypasses the outer and middle ear, allowing for sound transmission even if these structures are affected by hearing loss. Bone conduction is a natural phenomenon that our bodies use to hear. It is also used in a variety of assistive technologies for individuals with hearing loss.

Distortional bone conduction involves the vibration of the cartilage in the external ear (CC). This method of sound transmission, while less common, provides an alternative pathway for sound to reach the inner ear, effectively bypassing the air conduction route.

Several factors can influence the sensitivity and effectiveness of bone conduction. These include:

• Static force: The amount of pressure applied to the skull can significantly affect bone conduction sensitivity.
• Placement: The specific location of the device on the skull can affect the transmission of sound, with the forehead generally less sensitive than the mastoid bone.
• Masking of the nontest ear: To isolate the effects of bone conduction, it is essential to prevent sound from reaching the non-tested ear.

The occlusion effect is mostly noticeable in the lower frequency range, below 1000 Hz. This is because low-frequency sound waves are longer and more easily trapped in the limited space of the ear canal when it is occluded, leading to a greater boost in perceived volume. Higher-frequency sound waves are shorter and less affected by the occlusion effect.

The occlusion effect is a major concern for both hearing protectors and hearing aids. It leads to a sensation of discomfort, often resulting in people discontinuing the use of these important devices. Efforts focused on reducing the occlusion effect are crucial for improving user acceptance and maximizing the effectiveness of hearing protection and hearing aids.

To mitigate the negative effects of the occlusion effect in hearing aids, several solutions have been developed. These include:

• Changing the style of the dome: Using open-style domes allows for greater air flow, reducing the occlusion effect.
• Shortening the length of the vent: A shorter vent reduces the volume within the ear canal, lessening the trapped sound.
• Increasing the vent diameter: A larger vent further reduces the sound trapped within the ear canal.