Noise induced hearing loss

By Marcello Cherchi, MD PhD

For patients

Exposure to loud sounds can cause hearing loss. In some cases this hearing loss is temporary, but often it is permanent. The louder the sounds, and the more frequent the exposure, the greater the likelihood that one will suffer hearing loss.

Since permanent hearing loss is by definition irreversible, it is far preferable to prevent such hearing loss by avoiding excessive noise exposure. If an individual is exposed to noise regularly, we suggest consultation with an audiologist for advice on preventative strategies such as custom ear plugs and/or noise canceling headphones.

When permanent hearing loss is present, it is appropriate to consult an audiologist regarding amplification strategies, such as a hearing aid. In cases of severe bilateral hearing loss, cochlear implantation (by an otolaryngologist) may be appropriate.

For individuals with sub-total hearing loss, we suggest these strategies for protecting the ears:

• Avoid loud noises. If you are wondering, “Is this noise too loud?” then it is probably too loud and you should remove yourself from that situation.
• Avoid abrupt pressure changes. The most common example cited for this is SCUBA diving. However, for most people, airplane travel is the more realistic concern, and for this we suggest wearing EarPlane ear plugs during airplane ascent and descent. (The EarPlane ear plugs are inexpensive and can be purchased over the counter.)
• Avoid ototoxic medications where medically feasible. If anti-platelet therapy becomes medically warranted (such as for cardiovascular disease), consider avoiding aspirin and instead using a non-ototoxic anti-platelet agent (such as clopidogrel, which requires a prescription).
• Have any ear infections treated promptly.

For clinicians

Overview

The cochlea functions as a frequency analyzing mechanoelectrical transducer, converting the changing pattern of kinetic energy from the vibrating motion of the tympanic membrane (driven by sounds of specific frequencies and amplitudes) into discrete neural (electrochemical) signals.  As such the cochlea is designed to function optimally within a given range of frequencies and amplitudes.  Inappropriately loud sounds (which can occur in many forms of social, recreational and occupational activities) can result in excessive kinetic energy being transmitted to the cochlea, resulting in structural damage, cellular damage and their sequelae.  There may be some component of genetic predisposition to noise-induced hearing loss.  Noise-induced cochlear damage can result in hearing loss, and sometimes tinnitus.  The degree of hearing loss can be quantified on audiometry.  The best management strategy is primary prevention.  After noise-induced hearing loss has occurred, secondary prevention consists of protecting the ear(s) by avoiding loud noises, abrupt pressure changes, and ototoxic medications, and treating ear infections.

Introduction

The cochlea functions as a frequency analyzing mechanoelectrical transducer, effectively converting the changing pattern of kinetic energy from the vibrating motion of the tympanic membrane (driven by sounds of specific frequencies and amplitudes) into discrete neural (electrochemical) signals. As such the cochlea is designed to function optimally within a given range of frequencies and amplitudes. Auditory function can be harmed by sounds carrying excessive kinetic energy.

Forms of noise exposure

Noise exposure comes in many forms during social, recreational and occupational activities (Basner, Babisch et al. 2014).

Mechanisms of noise induced hearing loss

When the kinetic energy of incoming sounds is excessive, the cochlea can suffer damage through several mechanisms (Ding, Yan et al. 2019). The first is structural damage (at the cellular level) directly resulting from mechanical forces. The second is a range of cellular insults from the chemical consequences of processing loud sounds, including oxidative stress, calcium overload and inflammatory responses.

Factors predisposing to noise induced hearing loss

It has been estimated that perhaps as much as 50% of noise induced hearing loss is made possible due to predisposing genetic factors (Basner, Babisch et al. 2014). Over 200 genes have been implicated as increasing vulnerability to noise induced hearing loss (Ding, Yan et al. 2019). The genes encode a variety of proteins, including those involved in the anti-oxidant system (for processing free radicals), potassium channel proteins, heat shock proteins and others.

Clinical manifestations of noise exposure

Exposure to loud sounds can induce hearing loss termed a threshold shift, meaning that a stimulus of greater amplitude is required to elicit the same perception. This hearing loss can recover in hours to weeks, and in such cases is designated a temporary threshold shift. The louder the sound, and the greater the time of exposure, the more likely it is that there will be a permanent threshold shift, meaning hearing loss from which one does not recover. Often noise exposure causes a combination of temporary threshold shifts (at some frequencies and amplitudes) and permanent threshold shifts (at other frequencies and amplitudes) (Ryan, Kujawa et al. 2016). Repeated noise exposure will tend to cause progressive hearing loss (Ding, Yan et al. 2019).

Tinnitus often accompanies hearing loss of any cause (Lockwood, Salvi et al. 2002), and noise-induced hearing loss is no exception (Basner, Babisch et al. 2014).

Diagnosis of noise induced hearing loss

Hearing loss can be characterized and quantified by audiometry. Most noise-induced hearing loss is sensorineural in nature. Very violent noise exposure, such as from blast injuries, can cause damage to the eardrum or ossicular chain as well, and in such cases the hearing loss will additionally exhibit a conductive component.

Noise induced hearing loss tends to affect high frequencies before low frequencies. However, many patients with noise-induced hearing loss exhibit a pattern that audiologists often term a “noise notch” (McBride and Williams 2001) which refers to a dip in hearing around 4 – 6 kHz, with better hearing below and above that range, irrespective of the particular pitch of sounds to which a person has been exposed. This is apparently attributable to the specific vulnerability conferred by the anatomical properties (with corresponding resonant frequencies) of the human external auditory canal.

Because of the general pattern of high greater than low frequency sensorineural hearing loss, it is often difficult to distinguish noise induced hearing loss from presbycusis (age-related hearing loss).

Non-auditory effects of noise exposure

Hearing loss is the perhaps the most obvious effect of noise exposure. But noise exposure has been shown to have a number of non-auditory consequences as well (Basner, Babisch et al. 2014), including adverse effects on cognitive function, sleep and cardiovascular health.

Management: Primary prevention

When noise induces hearing loss, it is not generally possible to predict whether the threshold shift will be temporary or permanent. Consequently, primary prevention is by far the preferable management strategy.

For individuals who engage in recreational or occupational activities with predictably excessive noise levels, we generally recommend consultation with an audiologist regarding protection with custom ear plugs or noise canceling headphones.

Management: Treatment and secondary prevention

Once permanent hearing loss has occurred, management shifts to treatment and secondary prevention.

A reasonable initial treatment of any hearing loss is amplification, often in the form of a hearing aid. Traditionally this care has been delivered by an audiologist, but in October of 2022 the first over-the-counter hearing aids became available in the United States. In cases of severe bilateral hearing loss, candidacy for cochlear implantation can be assessed by an otolaryngologist.

We also suggest that an individual with hearing loss follow these strategies for protecting their ears:

• Avoid loud noises.
• Avoid abrupt pressure changes. The most common example cited for this is SCUBA diving. However, for most people, airplane travel is the more realistic concern, and for this we suggest wearing EarPlane ear plugs during airplane ascent and descent. (The EarPlane ear plugs are inexpensive and can be purchased over the counter.)
• Avoid ototoxic medications where medically feasible. If anti-platelet therapy becomes medically warranted (such as for cardiovascular disease), consider avoiding aspirin and instead using a non-ototoxic anti-platelet agent (such as clopidogrel).
• Have any ear infections treated promptly.

References