Generality
Hearing loss consists of the inability, partially or totally, to perceive a sound in one or both ears. Some people are born with a hearing impairment (congenital hypoacusis), while others may develop it gradually with advancing age (presbycusis) or as a consequence of illness or physical trauma.
Diagnosis helps determine the severity of the hearing problem. The doctor or a specialist can advise the adoption of a series of measures to improve the problems of conductive type, but in some cases it is impossible to reverse or prevent the hearing loss.
How hearing works
To understand how hearing loss occurs, it is first of all important to learn the mechanisms that allow us to perceive an auditory sensation.
The sound consists of pressure waves conducted through air or water. The ear transforms these sound waves into auditory nerve impulses, which are transmitted to the brain. Anatomically, in humans the ear is divided into three main areas:
- Outer ear : formed by auricle and auditory canal. Thanks to its structure, it allows to convey the sound waves towards the membrane of the eardrum, which provides the surface for sound collection and vibrates in response.
- Middle ear : transmits the mechanical vibratory energy of sound. It consists of a system of three auditory ossicles (hammer, anvil and stirrup), which amplifies and transfers the vibrations coming from the eardrum to the oval (or round) window, an opening in the bony wall of the middle ear cavity.
- Inner ear : in addition to controlling balance, it is responsible for transducing the mechanical vibratory energy of sound into nerve impulses. The auditory ossicles amplify the vibrations and lead the stimulus to the inner ear, through the fluid contained in the cochlea (endolymph), a snail-shaped structure located in the inner ear. Hairy (or ciliated) cells located in the cochlea move in response to oscillations and help transduce the sound wave into an electrical signal that is transmitted from the state-acoustic nerve to the brain.
When the problem occurs at the level of the cochlea or along the acoustic path, nerve deafness occurs (central). In this case the vibrations continue to reach the oval window, but the receptors do not respond or emit responses that do not reach the destination, ie the brain. Certain drugs are able to penetrate into the endolymph and can destroy receptors. Even bacterial infections can damage hairy cells or nerve structures.
Types of Hearing Loss
There are three main types of hearing loss:
- Transmissive hearing loss : occurs when the sound is not conducted efficiently from the outer ear to the inside (eardrum and acoustic bones are involved), often as a result of an obstruction determined, for example, by a wax plug or by a fluid build-up due to an ear infection. Transmissive hearing loss usually involves a reduction in sound level and sounds are perceived as weak.
- Sensorineural hearing loss : reduces the ability to hear weak sounds and occurs when hair cells in the inner ear (cochlea) or nerve pathways suffer damage. Sensorineural hypoacusis is the most common type of permanent hearing loss and is necessary above all as a consequence of the natural aging process or of a trauma;
- Mixed hearing loss : sometimes, transmissive hearing loss occurs simultaneously with sensorineural hearing loss. In other words, there may be damage in the middle or outer ear and in the inner ear (cochlea) or at the level of the auditory nerve.
Gravity levels
Hearing loss can be mild, moderate, severe or profound . The level of hearing loss in a person is determined by performing a hearing test to determine the sound, measured in decibels (dB), which the patient is able to hear. Some ear disorders, such as tinnitus, do not necessarily cause hearing loss.
- Mild hypoacusis (acoustic deficit between 25 and 39 dB). A slight hearing loss can sometimes make it difficult to follow a speech, especially in noisy situations.
- Moderate hypoacusis (acoustic deficit between 40 and 69 dB). In this case, the patient may have difficulty following the speech without using a hearing aid.
- Severe hearing loss (acoustic deficit between 70 and 89 dB). People who are severely deaf usually need to use some form of alternative communication, such as reading lips or using sign language, even with the use of a hearing aid.
- Deafness or deep hearing loss (acoustic deficit> 90 dB). Subjects who are completely unable to hear a sound can often benefit from a cochlear implant.
To provide an idea, it may be useful to compare the levels of acoustic deficit with some familiar sounds:
| Sound intensity of some common noises | |
| decibel | Noise source |
| Safety range | |
| 20 | Clock ticking |
| 30 | Whisper |
| 50-60 | Normal conversation |
| 80 | Sound of an alarm clock |
| Risk range | |
| 85-90 | Hairdryer |
| 100 | Snowmobile, rock concert |
| 110 | Striker hammer |
| Injury range | |
| 120 | Ambulance siren |
| 140 (pain threshold) | Jet |
| 180 | Rocket launch |
Sounds approaching 100 dB can cause hearing damage.
Symptoms
Hearing loss may be present at birth or develop at a later stage in childhood or adulthood. The symptoms of hearing loss may vary depending on the cause. Hearing loss can develop gradually over time, particularly due to factors associated with exposure to noise and age. Hearing loss can occur more quickly if connected to the presence of excess ear wax, infections or diseases in the middle ear.
Signs and symptoms associated with hearing loss may include:
- Some sounds seem muffled;
- Difficulty understanding words and following conversations, especially when there is background noise or you find yourself among a crowd of people;
- Others are often asked to speak more slowly, clearly and loudly;
- There is a need to increase the volume of the television or radio.
Other symptoms include:
- Dizziness or a lack of balance (more common in Ménière's syndrome and acoustic neuroma);
- Pressure in the ear (due to an alteration of the fluid behind the eardrum);
- Ringing in the ears (tinnitus).
Symptoms in children
Signs of hearing loss in children
Children are regularly screened within the first few weeks after birth as part of the neonatal auditory screening program (NHSP).
However, some signs may suggest considering a further hearing assessment, for example if you notice that the child:
- He is not afraid of loud noises;
- Within four months of life, he does not spontaneously turn to a sound source;
- It shows a delay in learning to pronounce the first words or these are not clear when it is expressed.
Causes
Some causes of hearing loss include damage to the inner ear, an accumulation of ear wax, some infectious diseases and the perforation of an eardrum.
Conductive hearing loss Transmissive hearing loss involves a reduction in sound level or an inability to hear weak sounds; occurs when the sounds are not able to pass into the inner part of the ear. This condition is often caused by an obstruction, which blocks the ear canal.
Some possible causes of conductive hearing loss are:
- Absence or malformation of the auricle, ear canal or middle ear;
- Presence of fluid in the middle ear;
- Ear infection (otitis media) or ear canal (otitis externa);
- Allergies (serous otitis media);
- Benign tumors;
- Swimmer's ear (external otitis).
Hearing loss can also be caused by:
- Gradual ear wax accumulation : it can block the ear canal and prevent the correct conduction of sound waves. A earwax cap causes hearing loss among people of all ages. This causes a slight hearing loss, which can easily be corrected by removing the excess ear wax.
- Rupture of the tympanic membrane ( perforation of the tympanic membrane ): sudden changes in pressure, traumatic lesions or infections can cause rupture of the tympanic membrane and, consequently, damage to hearing.
- Otosclerosis : a hardening of the bracket in the middle ear makes sound transmission less effective.
Sensorineural hearing loss. Sensorineural hypoacusis occurs when the hair cells inside the cochlea or the nerve pathways connected to it are damaged.
The following are examples of conditions that can cause sensorineural hearing loss:
- Congenital deafness : some people may experience an acoustic deficit from birth or experience the condition over time, due to genetic factors (such as Down syndrome or Usher) or some complications arising during pregnancy and childbirth.
The non-hereditary factors can be: gestational diabetes or maternal infections, low birth weight, neonatal asphyxia (lack of oxygen at the time of birth), improper use of ototoxic drugs during pregnancy and severe jaundice in the neonatal period (can damage the auditory nerve in the newborn);
- Acoustic trauma : prolonged exposure to loud noises can cause damage to the inner ear;
- Presbycusis : age-related hearing loss is caused by degeneration of sensory cells;
- A head injury and ear injuries can cause hearing loss;
- Infectious diseases of the inner ear (such as meningitis, measles and mumps) or auditory nerve (rubella, encephalitis) can induce hearing loss, especially during childhood;
- Chronic otitis: can lead to hearing loss. In some cases this condition can also lead to serious life-threatening complications, such as brain abscesses or meningitis;
- Ménière syndrome : it is a pathology in which the patient suffers from vertigo and hearing loss has a variable course and is associated with tinnitus and feelings of obstruction in the ear;
- Acoustic neurinoma : a benign tumor that can involve the auditory nerve;
- Neurological disorders such as multiple sclerosis and stroke can have an effect on hearing.
The use of ototoxic drugs at any age - such as some cytotoxic agents, antibiotics and antimalarials or diuretics - can damage the inner ear. Certain chemotherapeutic drugs and high doses of aminoglycosides (example: neomycin or gentamicin) can damage the cochlea and the auditory nerve, causing sensorineural hearing loss. Temporary hearing effects can also occur if very high doses of aspirin or other painkillers are taken.
Age-related hearing loss
Aging is the main cause of hearing impairment. This condition is known as presbycusis . Some people begin to gradually lose their hearing from the age of 30 to 40 and the disorder is accentuated as they age. Most of the subjects, at the age of 80, have significant hearing problems. Age-related hearing loss occurs when nerve cells or hair cells inside the cochlea gradually degenerate and die. When these components are damaged or missing, the electrical signals are not transmitted as efficiently and hearing loss occurs. High-frequency sounds, like the voices of female or children's people, can become difficult to hear. It may also be difficult to understand consonants (such as the letters s, t, pef). This type of hearing loss is permanent.
Acoustic trauma
Another common cause of hearing loss is ear damage caused by excessively loud noises. This phenomenon is known as acoustic trauma and can occur when part of the delicate internal structure of the ear is damaged. After prolonged exposure to loud noises, the hair cells of the cochlea become inflamed and undergo wear. The noise level of the noise and the duration of exposure are important factors in determining an acoustic trauma.
In particular, those who are at risk of developing an acoustic trauma are those:
- who work with equipment that produces excessive noise, such as pneumatic hammers or special machinery used in agriculture, construction or factory work. If exposure to a loud noise is a normal component of the work environment there is a greater risk that damage may occur inside the ear. Even explosions (example: fireworks) or firearms can damage hearing immediately and permanently;
- who work in environments where there is loud music, such as night club staff;
- who listen to loud music with earphones. Other recreational activities with dangerously high noise levels include snowmobiling or motorcycling.
Hypoacusis and Hearing Loss - Diagnosis and Treatment »
