Hearing Loss in Adulthood Notes

Rates of Hearing Loss

• Acquired Hearing Loss

  • Noise-induced hearing loss

  • Presbyacusis (age related hearing loss)

Acquired Hearing Loss

• The Invisible Handicap

• Estimate: 8% of population (>15 years) in developed countries

  • Significant losses (>35 dB)

  • About 330,000 people in NZ

• Reference: Stevens, G., et al. (2013). Global and regional hearing impairment prevalence: an analysis of 42 studies in 29 countries. European Journal of Public Health, 23(1), 146-152.

Global Patterns of Hearing Loss

• Graphs showing the prevalence of hearing impairment (%) as a function of age (years) and dB HL.

Acquired Hearing Loss Details

• About 24% of adults have some hearing loss

  • 8% Moderate or worse

  • 16% Mild

• Mostly age-related (Presbyacusis)

  • About five out of six cases of hearing loss

  • Unavoidable but may be modifiable

    • e.g. Smoking may increase the risk

• Most other cases noise-induced

  • About one in six cases of hearing loss

  • Completely avoidable

• Reference: Dawes, P., et al (2014). Cigarette Smoking, Passive Smoking, Alcohol Consumption, and Hearing Loss. Jaro-Journal of the Association for Research in Otolaryngology, 15(4), 663-674

Meaning of “Noise” in Audiology/Acoustics

1. Sound that potentially damages the ear

2. Sound with spectral energy distributed at random

3. Sound that masks other sounds

4. Sound that is unwanted

• In general usage, noise is random variability in a signal.

• Examples:

  • High-level sound

  • Masker

  • Damaging

  • Unwanted

  • Spectral

Noise-Induced Hearing Loss (NIHL)

• Below 70 dB SPL - no NIHL

• In large samples, NIHL tends to be more pronounced around 3–5-kHz

• Postulated mechanisms:

  • Adaptation (temporary)

  • Mechanical damage

  • Excitotoxic damage

• Loss of cochlear sensory hair cells

• Loss of auditory nerve fibres

The Ear

• Diagram of the ear showing the outer ear, middle ear, and inner ear.

• Key components labeled:

  • Outer Ear: Ear Canal, Tympanic Membrane

  • Middle Ear: Malleus, Incus, Stapes, Middle-Ear Cavity (air), Eustachian Tube

  • Inner Ear: Cochlea, Auditory Nerve

Inner Ear - Cochlea

• Diagram of the cochlea showing:

  • Oval window

  • Round window

  • Cochlear duct

  • Perilymph space

  • Endolymph (within membrane)

  • Cochlear nerve

  • Modiolus

  • Scala tympani

  • Vestibular (Reissner's) membrane

  • Scala vestibuli

  • Tectorial membrane

  • Basilar membrane

  • Hair cells

  • Supporting cells

  • Organ of Corti

Organ of Corti

• Image showcasing the structure of the Organ of Corti.

Mechanical Damage to the Organ of Corti

• Microscopic image showing mechanical damage to the organ of Corti (20μm, 2010).

Sensory Cells Die

• Image illustrating that sensory cells die and the organ of Corti seals where they were.

Excitotoxic Damage

• Excitotoxic damage to synapses and the auditory nerve

  • Control

  • 1 day post-exposure

  • 2 wks post-exposure

  • 64 wks post-exposure

  • Synaptic Ribbons

  • IHC

  • Ganglion Cells

  • merge red CtBP2 NF-H 50 μm

  • merge 10 μm red

• Reference: Kujawa and Liberman, 2007

Typical Noise-Induced Hearing Loss

• Mild notched high-frequency hearing loss in early stages, progressing to broader notch and greater loss in very high frequencies with additional noise exposure.

• o = right ear, x = left ear

Exposure Time and Noise Level

• Legal exposure in workplaces: Eight-hour equivalent A-weighted sound pressure level of 85dB(A)

• Every 3 dB increase reflects a doubling of the sound level, so “safe” exposures are:

  • 4 hours at 88 dB

  • 2 hours at 91 dB

  • 1 hour at 94 dB

  • 30 minutes at 97 dB

  • 15 minutes at 100 dB

  • 7 ½ minutes at 103 dB

  • 4 minutes at 106 dB

  • 2 minutes at 109 dB

• 109 dB is the level of most live concerts and dance clubs

Epidemiology of NIHL

• WHO estimates:

  • >466 million people have significant hearing loss (2018)

  • Approximately 16% of these have NIHL

• NZ estimates:

  • Hearing impairment costs NZ $4.9b annually (2016)

    • $1b direct financial loss

    • $3.9b loss of wellbeing

  • NIHL may account for about 30% of cost

Prevention of NIHL

• Noise-induced hearing loss cannot heal in mammals – Including humans

• Effect is insidious – People often don’t realise it is happening

• Hearing aids cannot properly replace good natural hearing – Analogy: crutches

• Prevention is the only cure

Three Key Aspects of Prevention of NIHL

• Eliminate

• Turn It Down

• Walk Away

• Isolate

• Minimise

• Protect Your Ears

Dangerous Decibels

• Fun and interactive training developed for children aged about 8-12 years

• Modular presentation

• 45-minute session

• Delivered by ‘Educators’ who undergo two days’ training

Dangerous Decibels Effectiveness

• Developed in USA and brought to New Zealand

• Produced sustained improvements in children (Martin, Griest, Sobel, & Howarth, 2013)

• Lacked effectiveness in teenagers (Griest, Folmer, & Martin, 2007)

  • Learned the information

  • Didn’t alter attitudes or behaviour!

Prevention: Teenagers and Adults

• Is possible

• Needs involvement!

• Works for teenagers if they teach younger children – Welch, Reddy, Hand and Devine (2016)

• Works for adults in high-noise workplaces – Reddy, Welch, Thorne, Ameratunga (2016)

Ecological Model of Health Promotion

• Policy (laws, regulations)

• Community (cultural values, norms)

• Organisational (environment, ethos)

• Interpersonal (social network)

• Individual (knowledge, attitude, skills)

Personal Audio Systems

• Very widespread use (phones)

• Increased levels in noisy environments

• Longer exposure

  • Long battery life

  • Infinite number of songs

• Digital Signal Processing

  • “Loudness War”

  • Reduced Dynamic Range (adaptation)

Output levels of music

• Graph showing output level (dBA) vs. Percentage of Volume Control for various devices.

• Grand Average: 101.8 dB

• Reference: Portnuff & Fligor

Personal Audio Systems History

• “Walkmans” etc have existed since the 1980s – No clear evidence of harm so far

• Phones have more widespread use

• Modern music characteristics may be more harmful

Presbyacusis: Age Related Hearing Loss

• Graphs showing the prevalence of hearing impairment (%) as a function of age (years) and dB HL.

Presbyacusis: Sex and Frequency Differences

• Graphs displaying Age-Related Permanent Threshold Shift (dB) by Frequency in kHz and Age (years) for both Males and Females based on data in International Standard ISO 1999.

• 12% of Men

• 10% of women

Presbyacusis: Is it really inevitable?

• Mabaans

• Intrafamilial correlations

• No 4-kHz notch

Presbyacusis: Types

• Sensory: Degeneration of the Hair Cells

• Neural: Degeneration of auditory nerve fibres

• Strial: Degeneration of the Stria Vascularis

• Inner Ear Conductive: Loss of flexibility of the Basilar Membrane

The Cochlea and Presbyacusis Types

• Diagram of the cochlea highlighting areas affected by different types of Presbyacusis.

  • Sensory

  • Neural

  • Strial

  • Inner Ear Conductive

NIHL vs Presbyacusis

• Graph comparing NIHL and Presbyacusis: The problem for diagnosis

  • -- no noise, 90%ile

  • 100 dBA, 50 %ile

Summary of Hearing Loss in Adulthood

• Sensorineural hearing loss is permanent

• Likelihood of developing noise-induced hearing loss depends on both duration of exposure and sound level

• Characteristic pattern of noise-induced hearing loss is a high-frequency “notch” in the audiogram – but this is not reliable for individuals.

• Even when people know that loud sound will damage their hearing, they often will not protect their hearing

• Training programmes can change behavior more easily in young children, but in teenagers and adults, they need broader involvement

• Presbyacusis increases with age, and more in men than women.

• It involves four processes: sensory, neural, strial, and inner ear conductive losses.