Many people think of hearing loss as only affecting older people, but it can affect anyone. There are many kinds of hearing loss with a lot of subtle overlap of the causes. Treatment is no longer restricted to hearing aids. There is innovative technology available with new strategies, such as working with cognition.
The perception of a hearing test is like that of a test of our vision, but there are crucial differences. Unlike a vision test which evaluates whether we see or not and how well we see, a hearing test has a wealth of information that gives us insight into the health of the ear. Someone may hear, but they do not understand what they hear, for instance. Everyone has a signature on their hearing test much like a fingerprint.
The basics of sound and hearing
We hear through in two distinct ways: sound conduction and bone conduction. Most of us think about hearing as just how we perceive sound through the air.
Sound is a vibration that causes an acoustic wave. That vibration is transmitted through different mediums, but we usually only consider air. But if you have ever been underwater you know that we hear a sound, just not as well. There is an entire interdisciplinary field of science that deals with mechanical waves such as sound called acoustics.
The sound generated travels through the air in different frequencies, high and low. The units of frequency are hertz (HZ). We as humans can hear sounds from 20Hz to as high as 20000 Hz. Frequency is the total number of waves produced in one second. A drum beat would have a lower frequency than a cricket.
The amplitude of the sound wave is the intensity of the sound. We are all familiar with that measurement which is in decibels (dB). Decibels are on a logarithmic scale so an increase of 10 dB causes a doubling of perceived loudness and that represents a ten-fold increase in the sound level.
Types of hearing loss
There are three main types of hearing loss and the last type is just an overlap of the first two. As we age, we tend to have a specific type of hearing loss which is due to noise exposure which is cumulative over our lifetimes.
Sensorineural hearing loss
All the sound that moves through the air is gathered by our external ear. That sound is conveyed to our hearing nerve called the cochlear nerve which sends its signals to the brain. When we have hearing loss that is affecting the transmission of sound to the brain it is called sensorineural hearing loss. Generally, there is not anything that we can do to improve that hearing loss once the hearing is gone, it is gone.
Sensorineural hearing loss can be due to hereditary causes, or more commonly from long-standing noise exposure. It can be subtle, slow in developing, and only affect the extremely high frequencies.
This is important to understand because without hearing in the high frequencies we lose our ability to not only hear high-pitched sounds like children’s voices but also, have difficulty hearing in noisy or crowded environments like family get-togethers or restaurants, for example.
Conductive hearing loss
As the sound is collected by our ears, it is also transmitted to the bones of our skull. This means the sound is conducted both through the eardrum and ossicles, or the tiny bones in our ears, and through the vibrations we feel. For that reason, in our clinic, we also call this bone conduction.
Someone can have conductive hearing loss with or without sensorineural hearing loss. Conductive hearing loss is often something that can be fixed. A simple example is when our ears have wax, and we cannot hear. We can still hear, but everything sounds muffled. Removal of the earwax solves the hearing loss in many cases.
Surgeons can repair many types of conductive hearing loss. These include repair of the ear canal, eardrum, or even the ossicles (small bones) behind the eardrum.
Restoration of hearing is very satisfying to both the patient and the doctor, but it is relative. The doctor cannot repair sensorineural hearing loss with the placement of an external implant such as a cochlear implant and that topic warrants another discussion.
Mixed hearing loss
Mixed hearing loss is both sensorineural hearing loss and conductive hearing loss. It is a combination of subtle differences between the two. Everyone who has mixed hearing loss has their signature hearing, with things they can hear in different situations.
The mixed hearing loss represents one of the best reasons for hearing healthcare. This includes not only taking care of our ears because of illness or trauma but also, most importantly, hearing protection from loud sounds.
Even the loud lawn mower will gradually affect one's hearing over time, adding to the loss of hearing in high frequencies and compounding any issues with conductive hearing loss such as simple earwax.
Hearing loss and cognition
Okay, here is the double whammy. The fact is many people reading this never want to admit to having hearing loss and they sure don’t want to admit to having lost their cognitive abilities. Denial and avoidance are powerful motivators.
Recently, there has been an increasing interest in the correlation between hearing loss and cognitive decline. It appears that this applies not only to the elderly patient in a nursing home but also to midlife hearing loss in average people.
The key takeaway message is that hearing loss modification such as hearing aids can have a positive impact, decreasing the risk of dementia in the general population. This is exciting news for those who might have noticed some changes in their hearing, particularly in crowded environments or at higher frequencies.
There are studies underway to determine why there may be a strong association between hearing loss and cognitive decline. It is a situation like what comes first, the chicken or the egg. Many audiologists are now adding a cognitive screening to a standard hearing evaluation which greatly improves overall results with hearing aids alone.