6. Hearing damage diagnosis, vulnerability &treatment
- 6.1 How is hearing damage diagnosed?
- 6.2 Are certain individuals particularly vulnerable to sound exposure?
- 6.3 How can sound-induced hearing loss be treated?
6.1 How is hearing damage diagnosed?
Sound-induced hearing damage is not limited to deafness or an inability to hear certain sounds, but also includes difficulties understanding speech in noisy environments, ringing in the ears (tinnitus) and hypersensitivity to loud sounds.
The initial damage caused by loud sounds is often small and causes slight hearing problems that disappear some time after the sound exposure, so these often go unnoticed.
With repeated exposure to loud sounds, hearing disturbances increase. By the time they are noticed, the damage has become permanent and almost always incurable.
Hearing loss can be measured by exposing the individual to sounds of different frequencies and recording the lowest sound level that is heard by the listener on a graph called an audiogram. These graphs show that sound-induced hearing loss commonly occurs at high frequencies, especially at 4000 Hz. However, many people may have normal hearing within the range of frequencies usually tested and yet have sound-induced hearing loss. To detect damage even earlier, measurements can be carried out at even higher frequencies.
Another method used to detect or monitor hearing damage is to measure directly how the body responds to sounds rather than asking the listener when they can perceive a given sound. Tests are often done by detecting the response by the ear to soft sounds. There are a variety of tests; some can give a quick but rough indication of hearing loss, and others give a more detailed measure of hearing loss at different frequencies.
Excessive exposure to loud sounds can not only damage the organ of the inner ear that converts sound into electrical impulses (cochlea) but also the part that contributes to balance and spatial orientation (vestibule). Balance involves the eye and the ear but also the neck muscles that keep the head stable. Hearing damage can therefore be assessed indirectly by creating a sound and measuring how the neck muscles react to it.
Temporary or permanent high-pitched ringing in the ear (tinnitus) induced by loud sounds can sometimes be the only indication of hearing damage in the early stage, which may then be accompanied by hearing loss with continued exposure. After exposure to very loud or sudden loud sounds, tinnitus appears rapidly and is often temporary. In opposition, when it results from continuous long-term sound exposure, tinnitus often only appears after several years but remains permanent (see also section 10.3).
To treat or alleviate tinnitus, electrical stimulation of the organ of the cochlea and different drugs have been tried as possible options but results are uncertain. Psychological therapies remain the most common treatment method and when tinnitus becomes permanent, wearing a hearing aid may also help.
Illustration of audiogram More...
6.2 Are certain individuals particularly vulnerable to sound exposure?
Illustration jackhammer worker
For instance, exposure to loud sounds in combination with other exposures to some chemical substances such as organic solvents, asphyxiants, heavy metals and medicines, or to vibrations, may produce more severe hearing impairment than would be expected as a result of sound exposure alone.
Being exposed to loud sounds and to organic solvents at the same time can lead to hearing loss, even if the sounds alone would cause little or no harm. This risk for hearing loss increases with the number of solvents involved.
Heavy metals tend to accumulate in the body and cause toxic effects.
- Mercury poisoning can have many consequences including hearing loss and deafness.
- Cadmium can cause hearing loss and the effect is greater if the exposure to loud sounds and to cadmium happens at the same time.
- Arsenic overexposure leads to hearing loss for low-pitched sounds and balance disturbances.
- Exposure to lead may affect the inner ear but scientific evidence is inconsistent.
Certain gases (asphyxiants) such as carbon monoxide and hydrogen cyanide impede oxygen transport in the body when breathed in. In animals, they have been found to increase the damaging effect of loud sounds on hearing. Such combined effects in humans have not yet been fully demonstrated.
People working with vibrating tools, such as jackhammers, can develop hearing loss. The effect is worse if exposure to vibration and to loud sounds occurs at the same time. It is unclear whether body vibration causes any damage.
- For instance, long antibiotic treatments against severe bacterial infections can cause irreversible hearing loss in people with specific genetic traits, particularly if they have previously been exposed to loud sounds.
- Some drugs used to treat cancer can also cause hearing loss, particularly for high-pitched sounds. Exposure to loud sounds during chemotherapy therefore significantly increases the risk of hearing damage.
- Other medicines that can damage hearing, to a lesser extent, include certain anti-inflammatory drugs, as well as drugs to prevent malaria and drugs for reducing water retention.
Studies have tried to identify genes that could be involved in sound-induced hearing loss but the results are not conclusive. Apart from specific genes, other genetically dependent factors that may influence sound-induced hearing loss are eye and skin colour, gender, age and height. For example, people with blue eyes and white skin seem to be inherently more vulnerable to noise-induced hearing loss than others.
Abnormal blood pressure levels have also been observed in combination with sound-induced damage but it is not clear whether it is a cause or a simultaneous effect.
6.3 How can sound-induced hearing loss be treated?
Several therapies used in the past to treat hearing loss have proved to be efficient in case of acute sound-induced hearing loss. These include ingestion of steroids or magnesium, and breathing in oxygen through a mask or inside a high-pressure chamber.
Recent progress in biology has lead to the development of new drugs with promising results. Several drugs with anti-oxidant properties, that prevent cell damage, have proven to be effective in animal experiments but further research is needed before they can be used to treat humans. Other new drugs that prevent cells from destroying themselves have also given good results in tests on animals as well as humans. More...