Chapter 030. Disorders of Smell, Taste, and Hearing (Part 14)

In the event that the hearing aid provides inadequate rehabilitation, cochlear implants may be appropriate. Criteria for implantation include severe to profound hearing loss with word recognition score ≤30% under best aided conditions. Worldwide, 20,000 deaf individuals (including 4000 children) have received cochlear implants. Cochlear implants are neural prostheses that convert sound energy to electrical energy and can be used to stimulate the auditory division of the eighth nerve directly. In most cases of profound hearing impairment, the auditory hair cells are lost but the ganglionic cells of the auditory division of the eighth nerve are preserved. ...
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Chapter 030. Disorders of Smell, Taste, and Hearing (Part 14) Chapter 030. Disorders of Smell, Taste, and Hearing (Part 14) In the event that the hearing aid provides inadequate rehabilitation,cochlear implants may be appropriate. Criteria for implantation include severe toprofound hearing loss with word recognition score ≤30% under best aidedconditions. Worldwide, >20,000 deaf individuals (including 4000 children) havereceived cochlear implants. Cochlear implants are neural prostheses that convertsound energy to electrical energy and can be used to stimulate the auditorydivision of the eighth nerve directly. In most cases of profound hearingimpairment, the auditory hair cells are lost but the ganglionic cells of the auditorydivision of the eighth nerve are preserved. Cochlear implants consist of electrodesthat are inserted into the cochlea through the round window, speech processorsthat extract acoustical elements of speech for conversion to electrical currents, anda means of transmitting the electrical energy through the skin. Patients withimplants experience sound that helps with speech reading, allows open-set wordrecognition, and helps in modulating the persons own voice. Usually, within 3months after implantation, adult patients can understand speech without visualcues. With the current generation of multichannel cochlear implants, nearly 75%of patients are able to converse on the telephone. For individuals who have hadboth eighth nerves destroyed by trauma or bilateral vestibular schwannomas (e.g.,neurofibromatosis type 2), brainstem auditory implants placed near the cochlearnucleus may provide auditory rehabilitation. Tinnitus often accompanies hearing loss. As for background noise, tinnituscan degrade speech comprehension in individuals with hearing impairment.Therapy for tinnitus is usually directed towards minimizing the appreciation oftinnitus. Relief of the tinnitus may be obtained by masking it with backgroundmusic. Hearing aids are also helpful in tinnitus suppression, as are tinnitusmaskers, devices that present a sound to the affected ear that is more pleasant tolisten to than the tinnitus. The use of a tinnitus masker is often followed by severalhours of inhibition of the tinnitus. Antidepressants have been shown to bebeneficial in helping patients cope with tinnitus. Hard-of-hearing individuals often benefit from a reduction in unnecessarynoise (e.g., radio or television) to enhance the signal-to-noise ratio. Speechcomprehension is aided by lip reading; therefore the impaired listener should beseated so that the face of the speaker is well-illuminated and easily seen. Althoughspeech should be in a loud, clear voice, one should be aware that in sensorineuralhearing losses in general and in hard-of-hearing elderly in particular, recruitment(abnormal perception of loud sounds) may be troublesome. Above all, optimalcommunication cannot take place without both parties giving it their full andundivided attention. Prevention Conductive hearing losses may be prevented by prompt antibiotic therapyof adequate duration for AOM and by ventilation of the middle ear withtympanostomy tubes in middle-ear effusions lasting ≥12 weeks. Loss of vestibularfunction and deafness due to aminoglycoside antibiotics can largely be preventedby careful monitoring of serum peak and trough levels. Some 10 million Americans have noise-induced hearing loss, and 20million are exposed to hazardous noise in their employment. Noise-inducedhearing loss can be prevented by avoidance of exposure to loud noise or by regularuse of ear plugs or fluid-filled ear muffs to attenuate intense sound. High-riskactivities for noise-induced hearing loss include wood and metal working withelectrical equipment and target practice and hunting with small firearms. Allinternal-combustion and electric engines, including snow and leaf blowers,snowmobiles, outboard motors, and chain saws, require protection of the user withhearing protectors. Virtually all noise-induced hearing loss is preventable througheducation, which should begin before the teenage years. Programs of industrialconservation of hearing are required when the exposure over an 8-h periodaverages 85 dB. Workers in such noisy environments can be protected withpreemployment audiologic assessment, the mandatory use of hearing protectors,and annual audiologic assessments. ACKNOWLEDGMENT The author acknowledges the contributions of Dr. James B. Snow, Jr., tothis chapter FURTHER READINGS Benton R: On the origin of smell: Odorant receptors in insects. Cell MolLife Sci 63:1579, 2006 [PMID: 16786219] Breer H et al: The sense of smell: Multiple olfactory subsystems. Cell Mol ...