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Cochlear Implants Jeffrey R. Scott, Ph.D. Ear Anatomy Hearing Physiology Hearing Physiology For a low frequency sound, the traveling wave peaks near the apex of the cochlea; for a mid-frequency sound, the peak is near the middle, and for a high frequency sound, the peak is near the base of the cochlea. Hearing Physiology Ear Function – Video 03:25 Deafness – Definition Deafness The lack or severe impairment of the sense of hearing. Deafness – Scope -Approximately 17 percent (36 million) of American adults report some degree of hearing loss. - There is a strong relationship between age and reported hearing loss: 18 percent of American adults 45-64 years old 30 percent of adults 65-74 years old 47 percent of adults 75 years old or older have a hearing loss. - Of adults ages 65 and older in the United States, 12.3 percent of men and nearly 14 percent of women are affected by tinnitus (ringing in the ears). - 15 percent (26 million) of Americans between the ages of 20 and 69 have high frequency hearing loss due to exposure to loud sounds or noise at work or in leisure activities. Children: - 2-3 out of every 1,000 children in the United States are born deaf or hard-of-hearing. Deafness - Types Conductive Hearing Loss Conductive hearing loss occurs when sound is not conducted efficiently through the outer ear canal to the eardrum and the tiny bones (ossicles) of the middle ear. Conductive hearing loss usually involves a reduction in sound level or the ability to hear faint sounds. Sensori-Neural Hearing Loss Sensori-Neural (or "nerve" hearing loss) results from damage to the hair cells, nerve fibers or both in the inner ear. This is the most common type of hearing loss and is often caused by aging or prolonged exposure to noise. It also can be caused by high fever, birth defects and certain drugs. People with sensorineural hearing loss can hear speech, but frequently have difficulty understanding it. The problem is usually compounded when background noise is present. Neural – Hair Cell Damage - Illnesses - Drugs that are toxic to hearing - Hearing loss that runs in the family (genetic or hereditary) - Aging - Head trauma - Malformation of the inner ear - Exposure to loud noise Neural – Hair Cell Damage Before and After Loud Sounds - The top electron microscope photo shows the tiny hair bundle on top of a healthy inner ear hair cell. Compare it to the bottom electron microscope photo of a sound-damaged hair bundle again on top of an inner ear hair cell. Deafness - Causes Hereditary disorders - some types of deafness are hereditary, which means parents pass on flawed genes to their children. In most cases, hereditary deafness is caused by malformations of the inner ear. Genetic disorders - genetic mutations may happen: for example, at the moment of conception when the father’s sperm joins with the mother’s egg. Some of the many genetic disorders that can cause deafness include osteogenesis imperfecta, Trisomy 13 S and multiple lentigines syndrome. Prenatal exposure to disease - a baby will be born deaf or with hearing problems if they are exposed to certain diseases in utero, including rubella (German measles), influenza and mumps. Other factors that are thought to cause congenital deafness include exposure to methyl mercury and drugs such as quinine. Noise - loud noises (such as gun shots, firecrackers, explosions and rock concerts), particularly prolonged exposure either in the workplace or recreationally, can damage the delicate mechanisms inside the ear. Trauma - such as perforation of the eardrum, fractured skull or changes in air pressure (barotrauma). Disease - certain diseases can cause deafness, including meningitis, mumps, cytomegalovirus and chicken pox. A severe case of jaundice is also known to cause deafness. Deafness - Causes Age-related hearing loss Hearing gradually becomes less acute as we age. This is normal, and rarely leads to deafness. Age-related hearing loss (presbycusis) typically begins with the loss of higher frequencies, so that certain speech sounds - such as ‘s’, ‘f’ and ‘t’ - end up sounding very similar. This means the older person can hear, but not always understand. Tinnitus is often associated with deafness Tinnitus means a sensation of ringing in the ears. Some of the causes of tinnitus include middle ear infections and damage to the ear from loud noises. Tinnitus may occur on its own, or in conjunction with hearing loss. Deafness – Diagnostic Tests Air Conduction, Conventional or Standard Audiometry This test is commonly used to measure the hearing of adults and older children. A range of test tones, from low to high frequency (perceived as "pitch"), is transmitted through earphones placed on or in each ear, and patients are asked to indicate with a hand raise, button push or verbal response when you hear each sound. This testing determines the very softest signals you can hear at each of the presented frequencies, and indicates frequency regions in which hearing may be impaired. The louder the sounds must be made to be heard, the greater the degree of hearing loss at that particular frequency or frequencies. The frequencies tested are those important for hearing and understanding speech and other environmental sounds. Bone Conduction If testing reveals a hearing loss, another type of headset, a bone vibrator, is used to determine hearing by bone conduction in order to determine the type of hearing loss. This device sends sounds directly to the inner ear, bypassing the outer and middle ear. If the sounds are heard better by bone conduction, the hearing loss is conductive in nature and is likely located in the outer or middle ear. If the sounds are heard equally well with the earphones and the bone vibrator, the hearing loss is sensorineural in nature. A combination of conductive and sensorineural hearing loss also may be present; this is called a mixed hearing loss. Deafness – Diagnostic Tests Word Recognition In addition to tests with tones, word recognition testing is usually performed to evaluate the ability to discriminate differences between the speech sounds of various words, and how clearly the words are heard. During this test, you will be asked to listen to and repeat words. Acoustic Immittance These tests are used to assess the status of the middle ear and related structures. A type of acoustic immittance test called, tympanometry, measures the movement of the eardrum to see if it moves normally when pressure changes are applied. Restricted eardrum movement could indicate a problem with the eardrum or middle ear structures. Acoustic reflex testing, a method of determining how the middle ear reacts to loud sounds also might be tested. Otoacoustic Emissions (OAEs) OAEs are used to assess the function of the cochlea. OAEs are typically present when hearing is normal or near normal, and are typically absent when there is a problem in the cochlea. Auditory Brainstem Response (ABR) ABR is a procedure used to measure hearing sensitivity and determine if the neural pathways within the brainstem are transmitting sound properly. This test is used to rule out auditoryneurological problems. Brainwave activity in the auditory centers of the brain is recorded in response to a series of clicks or tones presented to each ear. During this procedure, electrodes are placed on the head to detect the electrical response of the brains to sounds presented while you rest or sleep. The electrodes do not cause pain or discomfort. Hearing Aids Amplification Only Indications for a Cochlear Implant - Adult - 18 years old and older (no limitation by age) - Bilateral severe-to-profound sensorineural hearing loss - Psychologically suitable - No anatomic contraindications - Medically not contraindicated Indications for a Cochlear Implant - Child - 12 months or older - Bilateral severe-to-profound sensorineural hearing loss - No appreciable benefit with hearing aids (parent survey when <5 yo or 30% or less on sentence recognition when >5 yo) - Must be able to tolerate wearing hearing aids and show some aided ability - Enrolled in aural/oral education program - No medical or anatomic contraindications - Motivated parents Structure of a Cochlear Implant Microphone Amplification External speech processor Compression Filtering Shaping Transmitter (outer coil) Receiver Electrode array Neural pathways Cochlear Implant Approximately 188,000 people worldwide have received cochlear implants. In the United States, roughly 41,500 adults and 25,500 children have received them. What is a Cochlear Implant? - Video 01:55 Cochlear Implantation XRay - Video 01:11 How does a Cochlear Implant Work? How does a Cochlear Implant Work? - Video 02:10 Activation - Video 02:50 Cochlear Implants Jeffrey R. Scott, Ph.D.