You recently starting talking too loud with your friends and you also felt you had to make efforts to hear them. You probably are developing hearing loss. You initially thought it was an effect of aging but you actually aren’t old enough to develop hearing loss. Sometimes, you heard a buzz in the ears. This became even worse when you walked home after your shift duty after working on machinery that produces loud noise. You fear you are losing your hearing. It’s time to take stock of the situation before it is too late.
The importance of hearing
Hearing is an important sensation. It enables communication, learning, speech, and language development. Children learn only because they hear. Those who cannot hear have impaired speech as well. Comprehension, understanding, and learning are impaired when hearing is compromised. Children with hearing impairment perform poor in school and lack social sense.
Structure and function of the ear
Ear is the apparatus for hearing. Ear comprises of three parts: the outer, middle, and inner ear. The visible (external) part of the ear is called the pinna. Positioned in the center of the pinna is a canal that carries sound waves into the ear. This is called the ear canal. The sound waves then strike the eardrum which separates the outer and the middle parts of the ear. In the middle ear are three tiny bones, called the malleus, incus, and stapes. When the sound waves strike the ear drum, it sets into vibration and further sends these vibrations to the bones in the middle ear. The movement of the bones intensifies the sound. The vibrations are next passed to the inner ear. A coiled structure called the cochlea in the inner ear participates in hearing. The cochlea is filled with fluid and has a membrane called the basilar membrane that runs through it and supports the hair cells. The hair cells have tiny bristle-like hair on their surface. The vibrations of sound cause the fluid in the cochlea to ripple which in turn cause the hair-like processes to tilt. This then allows the movement of certain chemicals into the cell which then creates an electrical signal. The nerve for hearing is called the auditory nerve, which carries the electrical signal to the brain where the sensation of sound is perceived and understood. Hair cells in cochlea have a differential detection of sound depending upon the location in the cochlea. Those near the base of the cochlea detect the high-pitched sounds like a shrill cry, and those near the apex of the cochlea detect the low-pitched sounds like a dog bark.
Effects of noise
Noise-induced hearing loss (NIHL) refers to a loss in hearing after exposure to loud sounds. Noise is inevitable in the modern times. The exposure to loud sounds causes discomfort whether it be for occupational or recreational purposes. Noise, either sudden or persistently loud, can lead to hearing loss.
NIHL occurs because the exposure to loud noise damages the hair cells in the cochlea. This hampers the translation of vibrations into electrical signals that can then be carried via the auditory nerve to the brain. In response to such noise exposures, the hearing loss may be transient, when it is called a temporary threshold shift. This disappears in about 16 to 48 hours after exposure to loud noise. There can also be a permanent hearing loss. The hearing loss may be accompanied by a sensation of other sounds in the ears. This is called tinnitus and may cause a ringing, buzzing, or roaring in the ears. The hearing loss and tinnitus may be present in one or both ears. Independent of hearing loss, the tinnitus may be transient or may last a lifetime.
Episodic exposure to a sudden blast or impulse and constant exposure to loud sounds can lead to NIHL. The intensity of sound and duration of exposure both determine the outcome. Regular exposure of more than 1 minute to 110 Decibels carries a risk of permanent hearing loss, unprotected exposure to 100 Decibels for no more than 15 minutes can be accepted but prolonged exposure to any noise above 90 decibels can cause gradual hearing loss.
Symptoms
Symptoms in NIHL may not be immediate as the damage progresses gradually. Some people complain of difficulty in understanding speech especially when there is a background noise. With advancing hearing loss, speech maybe difficult to understand even in quiet surroundings. There may be pain or tinnitus in the ears after exposure to loud sound. NIHL may be deceptively silent and may be picked up only upon testing.
Diagnosis
NIHL can be diagnosed by doing an audiogram. This is a test for hearing done at various sound frequencies. The frequencies tested are 0.5 kHz, 1 kHz, 1.5 kHz, 2 kHz, 3 kHz, 4 kHz, 6 kHz, and 8 kHz. The audiogram yields a curve for hearing. A typical sign of NIHL is the appearance of a “notch” in the curve of audiogram at 3000, 4000, or 6000 Hz, with recovery at 8000 Hz. The notch may vary in position on the curve depending upon the length of the ear canal and the frequency of the damaging sound. In NIHL, the hearing is better at 500, 1000, and 2000 Hz than at 3000, 4000, and 6000Hz, and the hearing level at 8000 Hz is usually better than the deepest part of the “notch.” Thus, the presence of high frequency hearing impairment after exposure to loud noise and an identifiable notch on audiogram are the criteria for the diagnosis of NIHL.
Prevention
NIHL can be prevented for sure. It is best to avoid noises that cause discomfort and are too loud. To keep safe, any noise above 85 Decibels should be avoided. Earplugs or earmuffs should be worn for protection when involved in loud activity. Children should specifically be protected from any loud noise. If there are any symptoms pertaining to hearing, a test for hearing should be done by a qualified and trained professional.
It is good to understand the hazards of noise and practice safe hearing in everyday life. NIHL is 100% preventable but not reversible after significant damage has occurred.
