Assistive Technology: Hearing Products

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Original Editors - Lucinda hampton

Top Contributors - Lucinda hampton, Naomi O'Reilly, Kim Jackson and Angeliki Chorti      

Introduction

Over 5% of the world’s population (430 million people) require rehabilitation to address their ‘disabling’ hearing loss (432 million adults and 34 million children). It is estimated that by 2050 over 700 million people (one in every ten people) will have disabling hearing loss.

• ‘Disabling’ hearing loss refers to hearing loss greater than 35 decibels (dB) in the better hearing ear.
• Nearly 80% of people with disabling hearing loss live in low- and middle-income countries.
• The prevalence of hearing loss increases with age, among those older than 60 years, over 25% are affected by disabling hearing loss.
• Only a fifth of people who would benefit from a hearing aid actually use one. Hearing loss is associated with social isolation and depression, which is suggested to be twice as prevalent in hearing loss. It has also been identified as an independent risk factor for cognitive decline and AD.

Definition

Hearing aids, by definition, are sound-amplifying devices that increase the user's ability to detect noise. The components of a non-invasive hearing aid vary widely but broadly consist of a microphone, amplifier, receiver, and battery. The microphone converts external acoustic energy into electrical energy, which is amplified by the amplifier. The receiver detects this and converts it back into acoustic energy, projecting sound into the ear canal. The amplification is driven by the battery, which can be made from zinc-air batteries, mercury, alkaline or rechargeable batteries. A non-invasive hearing aid aims to increase the sound levels delivered to and hence detected by the hair cells in the cochlea.

Function

Hearing aids may be indicated in various pathologies that cause sensorineural hearing loss, conductive hearing loss, or single-sided hearing loss.

Selection

There are various hearing aids, and their selection is not a ‘one-size fits all’ approach. Selection is influenced by factors that include audiometric deficit (laterality, frequency, and degree of loss), cosmesis, and the patient’s needs, lifestyle, and priorities.

Types 

Behind the ear (BTE) hearing aids sit behind the pinna. A plastic tube connects the hearing aid to an earmold or ‘open’ silicone ear tip according to the patient's needs. They are commonly used because they are capable of various levels of amplification, and their power and performance can be modified relatively easily. They are robust, cheap, and easier to manipulate for patients with reduced dexterity. Patients who require amplification for moderate to profound hearing losses will require an earmould, which may be less cosmetically appealing than the open fitting option.

The receiver in the canal (RIC) hearing aids are similar to the BTE, except the receiver is located at an ‘open’ silicone earpiece that sits in the canal, rather than inside the hearing aid casing near the microphone and amplifier. This set up allows higher amplification levels without the risk of acoustic feedback (sound escaping the canal and circling back through the hearing aid again), thus more suited to patients with high frequency ski-slope’ hearing losses and those who prioritize cosmetics of the device.

In the ear (ITE), in the canal (ITC), and completely in the canal (CIC), hearing aids are broadly grouped as custom-shape hearing aids. These are the most discrete hearing aids and, therefore, advantageous in a patient population that prefers an improved aesthetic. They can be used in a range of hearing losses, and because the receiver is closer to the eardrum, there is better amplification of high frequencies, important for speech discrimination. This is useful in environments that have a high level of background noise and in patients with presbycusis. However, like RIC and open canal hearing aids, custom-made hearing aids may not be suitable if large amounts of amplification are needed, as they use smaller batteries.

Finally, contralateral routing of signals (CROS) and bilateral contralateral routing of signals (BiCROS) are used for unilateral hearing loss and asymmetrical hearing loss, respectively, in cases where a conventional hearing aid provides little benefit. Here, a microphone is placed on the side of worse hearing, and the signal is transmitted to the better hearing ear, where this signal is amplified.

Modern Advances

Hearing aids, like everything else, are advancing in leaps and bounds. This is helped along by the fact that a hearing aid is basically a computer dedicated to processing sound. Some modern hearing aids can process sound at over a billion operations per second!

All this power is dedicated to cleaning up sound in a way that makes it easier for people to hear despite hearing loss.

Better sound quality: Many hearing aid computers are now able to process more sound than before. So fewer compromises need to be made to fit all the sounds of life into the hearing aid’s processing. With this improvement clients are able to hear the soft-spoken or distant speech without having to ask for as many repeats.

More connected: Connectivity of hearing aids to mobile phones has been around for several years. Many of today’s hearing aids have the ability to connect directly to mobile phones (particularly iPhone, although Android options are starting to appear) for wireless phone calls and music streaming using Bluetooth. There is also the option of downloading a phone app, which will allow control of your hearing aid via the phone.

Smaller: Improvements in technology are also bringing us smaller hearing aids. Not only ‘in the ear’ models, but also on ‘over the ear’ models. Even more powerful hearing aids have been shrunk. So now people have the option to wear their hearing aids more discretely and with more confidence.

Rechargeable Hearing Aids: Many manufacturers have introduced rechargeable models, and in 2021 there are ‘in the ear’ models being released with rechargeable technology. This means there are more options for more convenience with less fiddly battery replacements while making hearing aids better for the environment.

More water-resistant: Advances in technology have not only been focussed on the computer that runs the hearing aid, but there have also been several improvements in the materials used to build the hearing aid housings. As moisture has traditionally been one of the biggest killers of hearing aids, most modern devices have improved reliability and durability due to these recent advances. While these advancements don’t mean you can swim with aids or submerge them in water, it does mean that hearing aids will be less susceptible to moisture damage.

More automatic: Faster computer chips mean more can be done in the same amount of time. Advances have also been made in how hearing aids analyse the environments people visit every day. By analysing the sound environment several times each second, a modern hearing aid can more accurately determine the correct settings for that particular environment. This means less fiddling is required to ensure clients are hearing as well as possible. This also helps in making the handling of the hearing aid much better than on older generations of devices.

Tinnitus masking built-in: Many people with hearing loss suffer from tinnitus. In the past, we did not have many options apart from the volume of the hearing aid itself to try and offer some tinnitus relief. Almost all modern hearing aids have tinnitus masking abilities built-in. This means that clients can choose when they want to introduce a masking signal to take the edge off your tinnitus. This is especially helpful in quiet environments, where tinnitus tends to be most annoying.

References 

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