Clinical applications of the auditory brainstem response. San Diego: Singular; Hood L, Berlin CL. Auditory evoked potentials. Texas: Pro-Ed; Handbook of auditory evoked responses. Boston: Allyn and Bacon; Auditory brainstem response. Diagnostic audiology principles, procedures and practices 1. Auditory brainstem response thresholds to air and bone conducted clicks in neonates and adults.
Am J Otology ;14 2 Bone conduction auditory brainstem responses in infants. J Laryngol Otol ; 2 Brain stem auditory evoked response III. Clinical uses of bone conduction in the evaluation of otologic disease. Ann Otol Rhinol Laryngol ; Auditory brainstem response to bone-conducted clicks in adults and infants with normal hearing and conductive hearing loss.
Scand Audiol ;24 3 Biostatistics: a methodology for the health sciences. New York: Wiley; Yang EY, Stuart A. A method of auditory brainstem response to bone-conducted clicks in testing infants. J Speech Lang Pathol Audiol ;14 4 Effect of vibrator to head coupling force on the auditory brainstem response to bone conducted clicks en newborn infants. Ear Hear ; Beattie RC. Scand Audiol ;27 2 A Comparison of auditory brain stem response thresholds and latencies elicited by air- and bone-conducted stimuli. The tympanic membrane TM is an oval, thin, semi-transparent membrane that separates the external and middle ear tympanic cavity.
The TM is divided into 2 parts: the pars flaccida and the pars tensa.
The manubrium of the malleus is firmly attached to the medial tympanic membrane; where the manubrium draws the TM medially, a concavity is formed. The apex of this concavity is called the umbo. The area of the TM superior to the umbo is termed the pars flaccida; the remainder of the TM is the pars tensa.
The usual primary purpose of pure-tone tests is to determine the type, degree, and configuration of hearing loss. Patients unable to cooperate because of young age or other conditions cannot undergo pure tone audiometry. They may need to have the auditory system tested by other methods. This test assesses sensitivity when the signal is transmitted through the outer, middle, and inner ear and then through the brain to the cortex.
Testing may be performed using headphones, insert earphones, or sound fields. Headphones are placed over the outer ear. Circumaural headphones have a large cushion and fit around the ear, contacting the head. These generally are used to reduce ambient noise. Supra-aural headphones are more common and rest on the ear or pinna, but they typically provide no ambient noise reduction and may collapse the ear canals.
Insert earphones are transducers housed in a small box approximately 2" by 3" by 0. The signal is transmitted down a tube to foam tips, which fit in the ear canal. Insert earphones help reduce collapsing ear canals, and they reduce ambient noise and crossover of auditory stimuli to the nontest ear via skull transmission. This form of testing is used with infants, toddlers, and other individuals with special needs for whom earphone use may be problematic.
During sound-field testing, an individual sits in the center of the room, facing forward, halfway between each speaker. Typically, visual-reinforcement audiometry toys light and animate when the child responds to sound ; conditioned-orientation response audiometry toys on both sides test localization ; or play audiometry various games, eg, dropping a block in response to sound are used. These conditioned responses to auditory stimulus provide reinforcement that allows for measurable responses and longer interest in the test situation.
Audiology Pure-Tone Testing
In a sound field, the auditory signals are warble tones or bursts of narrow-band noise. Pure tones cannot be used because they can create standing waves in a sound field, which can alter signal intensity. Sound-field testing may also assess hearing aid benefit. Placing the person in the center of the room facing the speakers yields aided thresholds. The difference between aided and unaided thresholds is termed functional gain. This technique assesses sensitivity when the signal is transmitted through the bones of the skull to the cochlea and then through the auditory pathways of the brain.
This type of testing bypasses the outer and middle ear. A small oscillator is placed on the forehead or more commonly, the mastoid bone. The device stimulates the bones of the skull, which in turn stimulates both cochleae.
The oscillator may produce a vibration that is perceived by the patient, thus eliciting a vibrotactile response instead of a response to the auditory stimulus. Crossover occurs when sound presented to the test ear travels across the head to the nontest ear. This occurs at approximately 40 dB for circumaural earphones across all frequencies. When hearing sensitivity is much poorer in the test ear than the nontest ear, the signal may cross over and be perceived in the ear with better hearing, thus yielding a false impression of the intended test ear's sensitivity.
Masking presents a constant noise to the nontest ear to prevent crossover from the test ear. The purpose of masking is to prevent the nontest ear from detecting the signal line busy , so only the test ear can respond. When a signal is presented to the test ear, the signal may also travel through the head and reach the cochlea on the other side. However the intensity of the signal from the test to the nontest ear can be reduced by the mass of the head.
This signal reduction is called interaural attenuation. For bone conduction, the interaural attenuation may be as low as 0 dB because the bones of the skull are very efficient at transmitting sound. Thus, any suspected difference in bone conduction between the test and nontest ears requires masking. Interaural attenuation for air conduction can range between 40 and 80 dB.
Masking should be used if the difference in air conduction in one ear and bone conduction in the other ear is 40 dB or greater.
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Thresholds obtained with masking in the contralateral ear are called masked thresholds and should represent the true threshold of the test ear. A masking dilemma occurs when masking from the nontest ear crosses over to the test ear and affects threshold testing for the test ear. In this case, a reliable masked threshold cannot be obtained and is referred to as the masking dilemma.http://leondumoulin.nl/language/owner/voyage-into-haiti-in-haitian-creole.php
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This phenomenon generally occurs only in the presence of a substantial conductive component to the hearing loss and is less problematic with the more common use of insert earphones. Presbycusis usually manifests as a bilateral and symmetric sensorineural hearing loss. Usually, the higher frequencies are most severely affected. Word recognition may be poorer than predicted from the audiogram. A person with presbycusis may have more difficulty with hearing aids than a younger patient with equivalent hearing loss.
Onset of presbycusis typically occurs in middle-aged or older patients. The condition is usually slowly progressive. This condition is marked by fluid in the middle ear space, which may be caused by inflammation of the middle ear lining or inadequate aeration of the middle ear space. Otitis media frequently results in flat or up-sloping conductive hearing loss.
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