Acoustic shock

Typical descriptions of an acoustic shock 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; a stabbing pain in the ear; tinnitus; hyperacusis; sensations of burning, numbness, tingling and a feeling of blockage in the ear; mild vertigo (dizziness, head spinning); nausea; muffled or distorted hearing; and a shock response with shaking, crying, disorientation, headaches and fatigue.

Symptoms generally fade within a few hours or days. In some cases, almost always associated with the development and persistence of hyperacusis, some of the symptoms can persist for months or indefinitely. Persistent symptoms can include pain in and around the ear, pain in the neck/jaw/face, tinnitus, balance problems or unsteadiness, headaches, facial numbness, a burning/tingling feeling in the ear or face, a feeling of pressure or fullness in the ear, an echo or hollow feeling in the ear, and rarely, a hearing loss.

Acoustic shock symptoms are involuntary, so they cannot be readily controlled, and subjective, so they cannot be easily objectively measured. The unusual symptoms may be 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 auditory hypervigilance, anxiety, depression, post traumatic stress reaction/disorder, fatigue, and anger.

An acoustic incident is usually a sudden unexpected loud sound, usually heard near the ear. It often causes a strong fright and is involuntarily perceived as threatening or highly traumatic. 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 call centre 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.

The primary cause of acoustic shock 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.

Persistent acoustic shock disorder symptoms are consistent with a condition called tonic tensor tympani syndrome (TTTS). With TTTS, the tensor tympani muscle is spontaneously active, rhythmically contracting and relaxing. This appears to initiate a cascade of physiological reactions in and around the ear without objectively measurable dysfunction or pathology. Symptoms consistent with TTTS can include: tinnitus; rhythmic sensations in the ears such as clicks and tympanic membrane (ear drum) flutter; alterations in ventilation of the middle ear cavity leading to symptoms in the ears of a sense of blockage or fullness, frequent "popping" sensations and mild vertigo; minor alterations in middle ear impedance (stiffness) leading to fluctuating symptoms of muffled or distorted hearing; irritation of the trigeminal nerve innervating the tensor tympani muscle, leading to pain, numbness and burning sensations in and around the ear, along the cheek, neck and temporomandibular joint (TMJ) area.

Our program involves:

• A detailed medical history to provide a definitive diagnosis of acoustic shock/acoustic shock disorder. As the symptoms are involuntary and subjective, evaluation and diagnosis is carefully considered for each patient.  
• A hearing assessment needs to be carried out with care.  For patients with severe acoustic shock, many sounds are painful, potentially leading to a temporary exacerbation of their TTTS symptoms.  Additionally, patients with severe acoustic shock are often unable to tolerate anything placed in or over their ears without temporary exacerbation of their symptoms.  As a result, an audiological assessment, requiring the patient to listen to sounds via headphones/earphones, is threatening and can lead to a significant temporary increase in symptoms. This can be a traumatic experience for the patient if the acoustic incident was sustained via headphones or a headset.  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 acoustic shock patients. An involuntary functional hearing loss emerging in the test condition is rare but not an unknown occurrence in these patients. 
• An evaluation of the emotional impact of acoustic shock/acoustic shock disorder is carried out, which screens for clinically significant levels of depression, anxiety and post traumatic stress disorder or trauma reaction.
• Acoustic shock patients are often bewildered and distressed by their symptoms.  To provide understanding and reassurance, a detailed explanation of acoustic shock is provided to our patients.  This includes a personalised explanation of the peripheral and central auditory system, including TTTS; hearing test results; and the neurophysiological basis of hyperacusis and tinnitus-related distress.
• A detailed report is provided when acoustic shock/acoustic shock disorder has been evaluated, 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.

Symptoms are 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 auditory hypervigilance. For severe acoustic shock disorder, psychological/psychiatric evaluation and treatment for anxiety, depression and post traumatic stress disorder may be required and referral will then be recommended.

The potential severity and persistence of acoustic shock disorder symptoms has significant clinical and medico-legal implications.  Call centres in Australia need to be aware of the ongoing risk of acoustic shock and the need for acoustic shock workplace management. To provide effective acoustic shock protection in the workplace, the following factors should be considered:

1. We provide an acoustic shock Audiological Workplace Program, which includes:

• A hearing assessment for employees and supervisors.
• An acoustic shock education program for employees and supervisors.
• An acoustic shock protocol to be followed if an employee develops symptoms consistent with acoustic shock, which includes an acoustic shock assessment and rehabilitation for the employee.  Rapid referral of an affected employee can help to control persistence or escalation of symptoms, as well as reduce anxiety among other staff members.
• An acoustic shock 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 their usual workplace duties.

2.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 acoustic shock.  An acoustician will be able to measure ambient noise levels and teach effective communication strategies to minimise ambient noise levels. 

3. 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. However, output limiting devices are not able to provide total protection against acoustic shock.  The dominant factors leading to acoustic shock appear primarily related to the unexpectedness of the acoustic incident and secondarily to a threat response to loud sounds outside the person’s control, rather than to high volume levels alone.  

4. Employees with persistent acoustic shock disorder symptoms remain vulnerable to a significant escalation of their symptoms should they be exposed to another acoustic incident. For this reason, they should not return to headset use, even with output limiting devices in place.  A gently graded return to handset duties can be attempted once symptoms have resolved.