TAILIEUCHUNG - Chapter 030. Disorders of Smell, Taste, and Hearing (Part 12)

The responses are measured in decibels. An audiogram is a plot of intensity in decibels of hearing threshold versus frequency. A decibel (dB) is equal to 20 times the logarithm of the ratio of the sound pressure required to achieve threshold in the patient to the sound pressure required to achieve threshold in a normal hearing person. Therefore, a change of 6 dB represents doubling of sound pressure, and a change of 20 dB represents a tenfold change in sound pressure. Loudness, which depends on the frequency, intensity, and duration of a sound, doubles with approximately each 10-dB increase. | Chapter 030. Disorders of Smell Taste and Hearing Part 12 The responses are measured in decibels. An audiogram is a plot of intensity in decibels of hearing threshold versus frequency. A decibel dB is equal to 20 times the logarithm of the ratio of the sound pressure required to achieve threshold in the patient to the sound pressure required to achieve threshold in a normal hearing person. Therefore a change of 6 dB represents doubling of sound pressure and a change of 20 dB represents a tenfold change in sound pressure. Loudness which depends on the frequency intensity and duration of a sound doubles with approximately each 10-dB increase in sound pressure level. Pitch on the other hand does not directly correlate with frequency. The perception of pitch changes slowly in the low and high frequencies. In the middle tones which are important for human speech pitch varies more rapidly with changes in frequency. Pure tone audiometry establishes the presence and severity of hearing impairment unilateral vs. bilateral involvement and the type of hearing loss. Conductive hearing losses with a large mass component as is often seen in middle-ear effusions produce elevation of thresholds that predominate in the higher frequencies. Conductive hearing losses with a large stiffness component as in fixation of the footplate of the stapes in early otosclerosis produce threshold elevations in the lower frequencies. Often the conductive hearing loss involves all frequencies suggesting involvement of both stiffness and mass. In general sensorineural hearing losses such as presbycusis affect higher frequencies more than lower frequencies. An exception is Meniere s disease which is characteristically associated with low-frequency sensorineural hearing loss. Noise-induced hearing loss has an unusual pattern of hearing impairment in which the loss at 4000 Hz is greater than at higher frequencies. Vestibular schwannomas characteristically affect the higher frequencies but any pattern of

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• Harrisons Internal Medicine
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• Anatomy and physiology of gustation
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