What is AS?
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 acoustic shock (AS). AS becomes an Acoustic Shock Disorder (ASD) if symptoms persist.
Call centre staff using a telephone headset or handset are vulnerable to AS because of the increased likelihood of exposure, close to their ear(s), to an acoustic incident. More generally, AS 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 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 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 generally fade within a few hours or days. In some cases, 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, 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.
AS symptoms are involuntary, so they cannot be readily controlled, and subjective, so they cannot be easily 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 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 ASD - Tonic Tensor Tympani Syndrome
The primary cause of AS 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 ASD 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. 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.