acoustic shock injury
Westcott, M: Acoustic shock injury (ASI), Acta Oto-Laryngologica, 2006
Acoustic shock and TTTS Guide for Medical Professionals
Background
With the rapid growth of call centres around the world, increasing numbers of call centre employees have been reporting an unusual cluster of symptoms following exposure to a sudden, unexpected, loud noise (acoustic incident) transmitted via the telephone line.
These neurophysiological and psychological symptoms are different to those occurring with a traditional noise injury, and have become known as an acoustic shock injury (ASI).
Call centre staff using a telephone headset or handset are vulnerable to ASI because of the increased likelihood of exposure, close to their ear(s), to an acoustic incident. More generally, ASI can occur following exposure to any sound which gives a severe fright, is perceived as threatening or associated with a highly traumatic experience.
Acoustic Shock Injury Symptoms
Typical descriptions of an acoustic shock injury include "like being stabbed with an icepick in the ear", " like being electrocuted in the ear". For those using a headset, the immediate reaction is to pull it off.
The initial symptoms can include a severe startle reaction with a head and neck jerk, in extreme cases, falling to the floor; pain in the ear/neck/arm; tinnitus; hyperacusis; sensations of burning, numbness, tingling and feeling of blockage in the ear; vertigo (dizziness, head spinning); nausea; a hearing loss or distorted hearing; and a shock response with shaking, crying, disorientation, headaches and fatigue.
Symptoms may fade within a few hours or days. In some cases they can persist for months or indefinitely. Persistent symptoms can include pain in the ear/neck/jaw/face, tinnitus, hyperacusis, balance problems or unsteadiness, headaches, facial numbness, a burning feeling in the ear or face, tingling, a feeling of pressure or fullness in the ear, an echo or hollow feeling in the ear, and a hearing loss.
ASI symptoms are involuntary, so they cannot be readily controlled, and subjective, so they cannot be easily measured. The unusual symptoms are frequently misunderstood or not believed. As a result of an inadequate understanding of the symptoms, and if they persist or escalate, secondary and long term psychological symptoms can develop. These can include phonophobia (abnormal fear of sound), auditory hypervigilance, anxiety, depression, post traumatic stress reaction/disorder, fatigue, and anger.
Repeated acoustic incident exposure can increase a person's vulnerability to ASI, as well as the degree and persistence of their injury. Pre-existing stress/anxiety, as well as fear of repeated incident exposure, can also increase vulnerability to ASI. Call centre staff are therefore particularly vulnerable, as their workplace can be stressful - the job is often repetitive, monitored, competitive and the calls they make are frequently unwelcome.
Acoustic incidents
An acoustic incident is any sound which is perceived as threatening or highly traumatic. It is usually a sudden unexpected loud sound, usually heard near the ear. It may be a sound which becomes threatening because it persists and cannot be avoided. Acoustic incidents through a telephone line can originate as feedback oscillation, fax tones, signalling tones, or even malicious whistle blowing by dissatisfied customers. If the background noise level is high, call centre operators need to turn up the volume of their headset, increasing their risk of exposure.
A Proposed Mechanism of ASI - Tonic Tensor Tympani Syndrome
The primary cause of ASI is considered to be excessive middle ear muscle contractions (stapedius and tensor tympani), in particular tensor tympani contractions, following exposure to a loud, unexpected sound. While the stapedial reflex is an acoustic reflex triggered by high volume levels, the tensor tympani reflex is a startle and protective reflex with a variable threshold to sound, which can be reprogrammed downwards.
ASI symptoms are consistent with a condition called tonic tensor tympani syndrome (TTTS). With TTTS, the tensor tympani muscle is spontaneously active, continually and rhythmically contracting and relaxing.
The symptoms of sharp pain in and around the ear, sensations of burning, numbness and blockage in and around the ear, tinnitus, vertigo and headache are considered to be due to TTTS causing an abnormal stimulation of the neurones of the branches of the facial, glossopharyngeal, vagus, trigeminal and cervical nerves innervating the tympanic membrane (ear drum) and ossicular chain (middle ear bones).
Our Audiology practice provides unique expertise in the evaluation and management of ASI clients and in ASI workplace consultancy. Ms Myriam Westcott is an audiologist with extensive experience in the rehabilitation of tinnitus, hyperacusis and phonophobia, the dominant symptoms of ASI.
ASI evaluation and management
Our program involves:
- A detailed medical history to provide a definitive diagnosis of ASI. Malingering is generally rare in ASI clients, with most desperate to recover from their symptoms. However, as the symptoms are involuntary and subjective, and generally a third party will be funding the evaluation and treatment of the injury, a definitive and careful diagnosis needs to be made.
- A hearing assessment needs to be carried out with care. For clients with severe ASI exposure to all loud, many moderate and some soft volume sounds is often painful, potentially leading to a temporary exacerbation of their TTTS symptoms. Additionally, many clients with ASI are unable to tolerate anything placed in or over their ears without temporary exacerbation of their symptoms. As a result, an audiological assessment, requiring the client to listen to sounds via headphones/earphones, could lead to a significant temporary increase in symptoms. Any suprathreshold audiological testing, including loudness discomfort testing, and in particular acoustic reflex testing due to the high volume levels required, should not be carried out with ASI clients.
- An evaluation of the emotional impact of ASI is carried out, which screens for clinically significant levels of depression, anxiety and post traumatic stress disorder or trauma reaction.
- To provide understanding and reassurance, we give a detailed explanation of ASI to our clients. This includes a personalised explanation of the peripheral and central auditory system, including how TTTS may have caused their symptoms; their hearing test results; the neurophysiological basis of hyperacusis, tinnitus-related distress, auditory hypervigilance and phonophobia.
- A detailed report is provided to evaluate ASI, including fitness for work place duties, recommendations for a personalised rehabilitation program and onward referral for further evaluation and management of medical and psychological symptoms as required.
ASI Rehabilitation
Symptoms are individually managed as follows:
- We provide therapy for the dominant symptoms of tinnitus and hyperacusis
- We provide audiological management of hearing loss, including hearing aid fitting if required
- We recommend medical management of symptoms such as pain and vertigo
- we provide management of psychological symptoms. These can include stress and sleep management strategies; and the personalised development of cognitive behavioural strategies to manage phonophobia and auditory hypervigilance. For severe ASI, psychological/psychiatric evaluation and treatment for anxiety, depression and post traumatic stress disorder may be required and referral will then be recommended.
ASI Workplace consultancy
The potential severity and persistence of ASI symptoms has significant clinical and medico-legal implications. Call centres in Australia are starting to become aware of the risk of ASI and the need for ASI workplace management. To provide effective ASI protection in the workplace, the following factors should be considered:
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We provide an ASI Audiological Workplace Program, which includes:
- A workplace ASI risk assessment.
- A hearing assessment for employees and supervisors.
- An ASI education program for employees and supervisors.
- An ASI protocol to be followed should there be evidence of injury to an employee in the workplace from the use of equipment, which includes an ASI assessment and rehabilitation for the employee. Rapid referral of affected staff can help to contain the anxiety leading to persistence or escalation of symptoms.
- An ASI reporting protocol to ensure that the employer can manage risk consistently and meet insurers' needs should a WorkCover claim arise.
- The protocol to be followed should an employee be considered potentially unfit to perform workplace duties.
- Workplace environment: Ambient noise management. The higher the levels of ambient noise, the higher the required volume level of the telephone headset amplifier for the caller's voice to be clearly audible, increasing the risk of ASI. An acoustician will be able to measure ambient noise levels and teach effective communication strategies to minimise ambient noise levels. We do not provide this service, but can recommend companies who do.
- Telephone headset protection to acoustic incidents. A number of output limiting devices have been developed to restrict maximum volume levels transmitted down a telephone line, and are of benefit to help reduce the probability of acoustic incident exposure. Technicians are available to evaluate and recommend appropriate devices. We do not provide this service, but can recommend companies who do.
The dominant factors leading to ASI appear related to the sudden onset, unexpectedness and impact quality of loudish sounds outside the person's control, rather than to high volume levels alone, so it is impossible to give a 100% guarantee of protection to an acoustic incident using these output limiting devices. Employees with persistent ASI symptoms remain vulnerable to an escalation of their symptoms following further acoustic incident exposure and for this reason should not return to headset use even with output limiting devices in place.