What Makes Us Hear – Detecting Hidden Hearing Loss
What Makes Us Hear – Detecting Hidden Hearing Loss: Hearing is built on complicated procedures that turn airborne sound waves into electrical impulses. These impulses are subsequently transmitted to the brain by our auditory nerve.
When sound waves enter the pinna, they proceed to the eardrum via the ear canal, a narrow passageway.
The eardrum is vibrated by the sound waves entering the ear, and the resulting vibrations are sent to the middle ear's three small bones. The malleus, incus, and stapes are the medical terms for these three skeletons.
The middle ear bones amplify sound vibrations and send them to the cochlea, a snail-shaped, fluid-filled structure in the inner ear.
The cochlea is split into upper and lower sections from the beginning to the end by an elastic partition.
This partition has been named basilar membrane as a first floor or foundation for other critical auditory structures.
An oscillation of cochlear fluid causes a wave in the basilar membrane that goes down the auditory nerve. Following this wave are the basilar membrane's sensors, the hair cells located above the membrane.
Higher-pitched sounds, such as a newborn wailing, are perceived by hair cells near the broad end of the snail-shaped cochlea. Those closer to the centre hear quieter sounds like a dog barking.
As the hair cells move up and down, microscopic hair-like projections (called stereocilia) collide and bend on top of the hair cells.
Bending creates pore-like canals at the tips of the stereocilia.
When this occurs, substances enter the cells and generate an electrical signal.
The auditory nerve relays this electrical signal to the brain, turning it into a sound we recognise and understand.
Detecting Hidden Hearing Loss
Audibility and intelligibility are the key characteristics that affect how well a person can hear. Hair cells, sensory cells in the inner ear, contribute to sound audibility, or how loud a sound must be to be perceived.
When a sound is heard, the hair cells send electrical signals to the cochlear nerve, which transfers the signals to the brain.
The acoustic signal's ability to be understood by the central nervous system is affected by how successfully the cochlear nerve transfers these signals.
It was previously considered that hair cell death was the primary cause of hearing loss and that cochlear nerve injury occurred only after hair cells were destroyed.
Audiograms, which have long been considered the gold standard for hearing assessments, provide information regarding the health of hair cells.
Patients with normal audiograms were regarded healthy even though they experienced difficulty hearing in noisy surroundings because nerve loss was thought to be linked to hair cell loss or dysfunction.
Experts now understand why the audiogram does not determine the auditory nerve's health.
This explains why some patients who complain of trouble understanding a discussion in a crowded pub or restaurant have a “normal” hearing test. Similarly, it explains why many hearing aid users who receive enhanced sounds have difficulty understanding speech.
When M. Charles Liberman, Harold F. Schuknecht Professor of Otology and Laryngology at HMS, and Sharon Kujawa, professor of otolaryngology at HMS, uncovered covert hearing loss in 2009, they changed the way scientists thought about hearing on its head.
According to their research, cochlear nerve damage occurs before hair cell loss due to ageing or noise exposure. Audiograms do not capture the total level of ear damage since they do not include information about the cochlear nerve.
Developing a model to forecast cochlear nerve damage
Maison and his colleagues employed a speech intelligibility curve to predict a person's speech score based on their audiogram in this investigation.
They then calculated the disparities between the expected and actual word recognition scores acquired from the patient's hearing test.
The researchers reasoned that the severity of these inconsistencies represented the level of a person's cochlear nerve damage or concealed hearing loss after accounting for several factors, including the cognitive deficiencies accompanying ageing.
The researchers then used nerve loss values from histopathology data from human temporal bones to build a predictive model based on a conventional hearing test.
The findings indicated a link between poorer speech outcomes and cochlear nerve injury.
For example, patients with Ménière's disease had the worst outcomes, consistent with temporal bone tests indicating severe loss of cochlear nerve fibres.
However, patients with conductive hearing loss, drug-induced hearing loss, or typical age-related hearing loss had mild to moderate aberrations. –
The landscape of concealed hearing loss research is changing.
According to the World Health Organization, more than 1.5 billion people worldwide suffer from some degree of hearing loss.
Some of these persons are not candidates for traditional hearing aids, particularly if they have mild to severe hearing loss in the high-frequency range.
Knowing the level of neurological damage should help physicians meet patients' communication needs and provide appropriate interventions, in addition to employing effective communication tactics.
Maison believes that by identifying individuals most likely to have cochlear nerve injury, this model can assist physicians in evaluating the effectiveness of traditional and newer hearing amplification solutions.
By analysing word performance results in loud rather than quiet contexts, the researchers expect to refine their model and offer better solutions.
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