Therapy Analysis - Hearing Loss & Tinnitus
The Sound of Silence
The human auditory system is both complex and multifactorial, involving many intricate aspects of the ear, giving humans the ability to distinguish small differences in volume and frequency over a large audible range.
..hair cells are vital to the conversion of sound waves into nerve impulses and once lost, they cannot be replaced by natural physiological processes..Sound waves entering the ear canal cause vibrations of the tympanic membrane, also known as the eardrum. These vibrations are transmitted via tiny bones (the ossicles) in the middle ear to the fluid in the hearing organ of the inner ear, the cochlea. These mechanical 'waves' from the middle ear are then propagated by the cochlea via movements in the fluid and membranes, inducing the movement of sensory hair cells in the organ of corti. Resultant action potentials trigger the release of neurotransmitters from these hair cells, which by acting on primary auditory neurons, convert the physical vibrations to electrical signals. After travelling to the brain via the auditory nerve, the electrical signals are interpreted as sound.
Conductive hearing loss occurs when mechanical difficulties prevent the transmission of sound waves to the cochlea. This can be a result of damage to the tympanic membrane or ossicles, or a build up of wax in the ear canal. Another common cause is infection; otitis media leads to the normally air-filled middle ear becoming filled with a glue-like fluid, preventing the normal movements of the tympanic membrane and ossicles.
Conductive hearing loss is often more treatable than sensorineural hearing loss, a condition that is usually caused by damage to the hair cells in the cochlea. These hair cells are vital to the conversion of sound waves into nerve impulses and once lost, they cannot be replaced by natural physiological processes. In the absence of hearing defects from birth, we are born with approximately 17,000 hair cells, and this number gradually declines with age. In fact, according to The Royal National Institute for the Deaf and Hard of Hearing (RNID), over 50% of people over the age of 60 experience a degree of hearing loss due to the natural, progressive loss of these cells. This age-related loss of hair cells is known as presbyacusis, and is the most common reason for sensorineural hearing loss. Damage to the auditory nerve can also result in sensorineural hearing loss, although this is far less common.
..over 50% of people over the age of 60 experience a degree of hearing loss..The inevitable decrease in hearing ability that comes with age can be significantly exacerbated by prolonged exposure to excessive levels of noise. This may occur in the workplace, or during leisure activities, but however it happens, it is more damaging than it may first appear. The muffling effect on hearing that lasts for 1-2 days after the event may not seem that significant as it recedes, but any temporary effect on hearing can signify that more permanent damage has taken place.
The dampening of hearing ability following acoustic trauma is referred to as a threshold shift, meaning that the threshold level of hearing, i.e. the quietest sound an individual can perceive, has been altered. This threshold shift can be temporary or permanent, and is often accompanied by a ringing or buzzing sound in the ears when no external sound is present. This is known as tinnitus. Although not yet fully understood, various theories exist to explain the presence of tinnitus. For example, it is possible that the auditory cortex of the brain adapts to the death of hair cells and subsequent decrease in sound signals, or that dysfunction of damaged hair cells may be responsible for the perception of phantom sounds. Regardless of cause, the condition can be incredibly debilitating, affecting sleep patterns and everyday activities such as reading. Perhaps the most well known sufferer, Beethoven, said of the his condition: "My ears whistle and buzz continually, day and night...such a condition is truly frightful." Tinnitus may temporarily arise as a result of high-blood pressure or stress, but is usually a result of noise- or drug-induced damage and can remain a permanent fixture that as yet cannot be cured.
NIHL is easily preventable by the use of ear-defenders in noisy working environments, or more discrete earplugs at loud music venues. With the increase in technological advances, musician's earplugs are now also available, which provide a predefined reduction in ambient noise by around 15 or 25dB, whilst maintaining the clarity. Sadly, hearing loss caused by the use of various ototoxic drugs is largely unavoidable at present. For example, platinum-based chemotherapeutics such as cisplatin, and aminoglycoside antibiotics have long been known to irreversibly damage hearing, but these life-saving drugs are still used in the absence of alternatives with fewer side-effects.
