What is Acoustic Shock?
In the early 1990s, co-inciding with the rapid growth of call centres around the world, increasing numbers of call centre employees were reporting an unusual cluster of symptoms following exposure to a sudden, unexpected, loud noise (acoustic incident)randomly 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 acoustic shock. Acoustic Shock becomes an acoustic shock disorder if symptoms persist.
Call centre staff using a telephone headset or handset are vulnerable to acoustic shock because of the increased likelihood of exposure, close to their ear(s), to an acoustic incident. More generally, acoustic shock can occur following exposure to any sound which gives a severe fright or is associated with a highly traumatic experience.
+Acoustic Shock Symptoms
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.
+A Proposed Mechanism of Acoustic Shock Disorder - Tonic Tensor Tympani Syndrome
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.