Acoustic trauma (acoustic trauma) – causes, symptoms & therapy

A blast trauma is caused by strong sound stimuli (over 140 dB) that only affect the hearing for one to three milliseconds and overload it. The sound pressure is so strong that it damages the inner ear.

There is thus an acute defect in the hair cells (sensory cells) of the organ of Corti, which represents the interface between signals from the nerves in the cochlea and the acoustic mechanical vibrations. A human ear has about 15,000 such hair cells in this area. In the event of a blast trauma, the eardrum and auditory canal are not affected.

causes

Any sound event that exceeds the physical stress limit of a hearing organ, ie the ability of the ear to adapt to the sound pressure up to a certain threshold level, leads to temporary or permanent hearing damage. Such an acoustic trauma can be caused by a wide variety of influences, such as pistol shots, blows to the ear, bursting tires, lightning strikes and explosions. The following applies: the louder the damaging sound event is and the more abruptly it occurs, the greater the likelihood of impairment.Here, the damage to the organ of Corti occurs due to a lack of oxygen and, as a result, a metabolic disorder of the hair cells, which causes their function to be disrupted. However, it is also possible that there is mechanical damage to the sensory cells, which occurs as a result of the tearing of the basilar membrane. This membrane is in turn the seat of the organ of Corti, which contains the receptors for auditory perception. Such damage can be irreversible, so that hearing for the particular frequency ranges processed by the affected hair cells is perpetually impaired. In addition, ringing in the ears can occur immediately after the event .

When to the doctor?

If the hearing ability is permanently reduced after a loud bang, a doctor must be consulted. In most cases, a loud noise causes a feeling of numbness for a few minutes. If relief sets in after just a few minutes, the ability to hear will normally completely regenerate within the next few hours. A doctor does not need to be consulted if hearing is fully restored within a few days.

If the feeling of deafness or severe hearing impairment persists for several hours, an injury to the ear canal is very likely and should be investigated. An injury to the inner hair cells is irreparable and should therefore be clarified by a doctor.

Acoustic trauma can lead to the emergence of fear . If the person concerned is unable to calm down emotionally and minimize anxiety, it is advisable to consult a doctor. If the affected person suffers a panic attack due to the reduced hearing ability, a doctor should be consulted. Shortness of breath , sweating, hysterical fits or aggressiveness are signs of emotional overload and should be treated by a doctor. If you have problems keeping your balance or if you experience persistent dizziness, you should see a doctor to have damage to the organ of balance in your ear examined.

symptoms and course

The symptoms of an acoustic trauma can be of different nature. This also includes tinnitus . In the case of tinnitus, the person affected perceives noises that have no external acoustic stimuli. Another symptom is hearing loss, which is associated with a significant reduction in hearing ability. There is also a feeling that the affected ear is blocked. A fleeting, stabbing pain in the ear can also occur with a bang trauma.

Hyperacusis, a pathological hypersensitivity to noises that a healthy auditory organ does not perceive as unpleasantly loud, is also a sign of a previous acoustic trauma. Disturbance of balance and dizziness are also relevant signs of the disease. However, the symptoms of an acoustic trauma often improve within the first few days. Symptoms rarely increase after the event. Nevertheless, permanent damage persists in about 50 percent of acoustic trauma cases. This primarily affects the high-frequency range.

Diagnose

A description of the triggering event as well as the course over time are often clear indicators for the diagnosis of an acoustic trauma. To examine the specific effects on the hearing organ, the ENT doctor will carry out an otoscopy (ear mirroring). This is followed by various diagnostic procedures for quantifying the hearing damage.

If there is an unclear finding after these procedures, further investigations are initiated. The otoacoustic emissions, which are measured using a small probe inside the auditory canal, provide information about the transferability of vibrations of an acoustic stimulus. Brainstem audiometry can also record the electrical responses of specific brain regions when the patient perceives certain sounds.

complications

A variety of complications can occur after acoustic trauma. Inflammation and major injuries to the basilar membrane and hair cells can already occur during the trauma. As a result, hearing is sometimes limited and only recovers slowly. A certain degree of hearing loss rarely persists even after successful trauma treatment . With sound pressure waves of 140 decibels and more, there is a risk of severe fractures in the inner ear. In particular, the auditory canals, the organ of Corti and the cochlea are at risk and can become inflamed as a result of blast trauma.

The treatment of acoustic trauma is also not risk-free. Complications mainly come from prescribed drugs such as hydroxyethyl starch and procaine, which can cause itching and severe kidney damage. If cortisone is prescribed, it can lead to an increase in blood pressure and an increase in blood fat levels. In addition, the susceptibility to infection increases. During surgical treatment via tympanoplasty, injuries to the outer, middle or inner ear can occur. Possible complications include ringing in the ears , dizziness, one-sided paralysis and a change in the sense of taste.

treatment and therapy

The treatment of acoustic trauma always depends on the degree of damage. Most of the time, infusions containing active substances that stimulate circulation and cortisone are administered. The cortisone counteracts any inflammation . Occasionally, high-dose cortisone can also be injected directly into the inner ear. If this form of therapy does not work, oxygen administered under conditions of overpressure can promise success.

Surgical therapy should be initiated when conservative treatment methods cannot achieve far-reaching positive effects, since a perilymph fistula or damage to one of the two inner ear windows can be diagnosed. A perilymph fistula causes a pathological connection between the middle ear and the perilymph space, in which the sensory cells of the hearing organ are integrated. This connection can result from damage to one or both of the inner ear windows that connect the middle ear to the inner ear. 

The surgical procedure for acoustic trauma is a tympanotomy. The eardrum is folded to the side under local anesthesia so that the middle ear can be examined for a tear in the membrane. If the treating doctor observes a corresponding damage, the affected membrane is sealed with connective tissue.

If treated early, the hearing recovers in the majority of those affected. However, many patients often continue to suffer from ringing in the ears despite therapy. If such noises are still present a few weeks after an acoustic trauma, there is a high probability that they will remain permanently.

prevention

Acoustic trauma can be prevented by avoiding places where there is a high level of noise pollution. Appropriate protection (earplugs, hearing protection headphones) should always be worn when visiting the discotheque, at concerts or at work that is exposed to increased noise levels.