Insight 16

Age-related hearing loss (ARHL) affects the majority of elderly individuals.  It is an insidious change that fosters reduced social interactions and isolation.  Studies now show that it is a significant risk factor for dementia.

Importantly, ARHL  is an age change that is mostly PREVENTABLE.  It is largely due to chronic or repeated exposure to loud noises throughout the lifespan.  Hearing aids are the standard treatment.  Unfortunately, they provide only a very minor improvement in hearing.  However, novel treatments with greater efficacy are on the horizon.

Background

We have a wealth of sensory organs that enable us to navigate our environment.  These organs provide perceptions of sight, sound, smell, taste, position in space, pain, temperature (hot/cold), touch, pressure, and vibration.  Although they are all important and are negatively affected to different extents by age, this blog is about the loss of sound perception. Importantly, this loss can be chiefly prevented.

From sound to speech perception

The ear converts mechanical waves in the air (sound) to electrical activity in the brain (speech perception).  The ear contains three chambers: a) outer, b) middle and c) inner.  The first two chambers maximize the mechanical waves and the inner chamber, called the cochlea, adds more sophistication and conversion to electrical activity.  Fibers of the auditory nerve relay electrical activity to the speech-specific region of the brain.

Age changes in the ear

ARHL results from deteriorative changes in the cochlea.  This sensory organ contains specialized cells called hair cells that exquisitely sense the frequency and amplitude of sound waves and relay them accurately via nerve fibers to the brain as understandable speech.  Within this system, there are two fairly well characterized age changes that distort speech  perception. 

The first well defined age change is the  disappearance or dysfunction of the hair cells.  The second, more recently identified age change, is the inability of nerve fibers to receive information from the hair cells.  The hair cells and the nerve fibers no longer communicate as expected.

Consequences of ARHL

Age changes result in altered speech perception.  Specifically, weak sounds are not amplified, strong sounds are not dampened and the specific frequencies associated with vowel and consonant sounds are passed to the brain in a blur.  In particular, there is a preferential reduction in processing of high frequencies used by consonant sounds (ch, th, sh, z). Speech comprehension becomes a challenge.  Loss of specific hair cells produces this change.

Another very disturbing change is the inability to hear in a noisy environment.  The ability to enhance local sound  (speaking to neighbors) and to dampen surrounding environmental noise (crowded room) is lost.  Loss of connections to the auditory nerve fibers produces this change.

Prevention of ARHL – Noise Avoidance

Avoidance of repeated or chronic exposure to loud noises largely prevents ARHL.  Sources of loud noises are many.  According to the CDC (cdc.gov) avoidable noises belong to specific categories such as a) daily activities e.g. high volume music on personal listening devices, b) events e.g. concerts, restaurants, bars, sporting events, movie theaters, and c) tools e.g. power tools, lawnmowers, leaf blowers, sirens, firearms, firecrackers.

Avoidance of loud noises is the most effective means for prevention of ARHL.  When this is not possible, a common sense approach is to dampen the loudness by use of earplugs and earmuffs and reduce the volume on personal listening devices.

Current Therapies

Hearing aids are the mainstay for treatment of mild to moderate hearing loss.  Current hearing aids (referred to as digital) are technologically more advanced than the older hearing aids (referred to as analog).  Both types work by amplifying sound, although the newer hearing aids claim to provide better sound clarity and ability to hear in a noisy environment.  Sadly, these claims are not met and only a fraction of the elderly with hearing loss are satisfied with their hearing aids.  Consequently, many do not use them. 

Present day hearing aids do not replicate the sensory activities of the cochlea.  In this regard, It is puzzling to experts in the field why hearing aids are still so ineffective.  Firstly, they argue that scientists already understand essential components of hearing loss. Secondly, the technology such as quantum computers, nanotechnology and AI is available for application to hearing loss. Furthermore, combination of the two could produce a hearing aid that compensates for hearing loss in all aspects, not just amplification. 

Future Therapies

Several biological therapies to reverse ARHL are under investigation.  These therapies include cell replacement of missing or dysfunctional hair cells, gene therapy  and addition of nerve growth factors to the cochlea.  Although successful in animals, there therapies await evaluation in man.

Summary

Approximately 70% of elderly experience some degree of hearing loss.  Repeated exposure to loud noises is the prime cause of age-related hearing loss.  Sadly, the use of digital hearing aids, which primarily amplify sound, helps only a small percentage of elderly. However, future therapies, whether biological treatments or technologically advanced hearing aids are possible.  A worthwhile goal of the healthcare community is commitment and funding to develop the ideal hearing aid.

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