Evaluation of Hearing

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What questions do you ask a patient presenting with hearing loss?

As with any evaluation, it is important to first obtain a history of the problem. Details such as onset, course since onset, ear(s) involved, exacerbating and relieving factors, and related symptoms are important. Also noted are the presence of tinnitus, dizziness and/or vertigo, aural fullness/pressure, and ear pain. A detailed family, medical, and social history, including noise exposure, should be obtained to identify risk factors. Also, patients should be asked about temporary or permanent functional changes involving other cranial nerves, in addition to a thorough cranial nerve examination. Recent trauma, either blunt or penetrating, may also produce hearing loss.

2

Describe the two general types of hearing loss. How are they different?

• 1.

  Conductive hearing loss (CHL) results from disruption in the passage of sound from the external ear to the oval window. Anatomically, this pathway includes the ear canal, tympanic membrane, and ossicles. Such a loss may be due to cerumen impaction, tympanic membrane perforation, a foreign body, otitis media, or ossicular abnormality. CHL is often correctable with medical or surgical treatment.

• 2.

  Sensorineural hearing loss (SNHL) results from otologic abnormalities beyond the oval window. Such abnormalities may affect the hair cells of the cochlea or the neural fibers of the eighth cranial nerve. Presbycusis, or hearing loss related to aging, is an example of SNHL. An eighth cranial nerve tumors may also lead to such a loss. SNHL are generally permanent and typically unmanageable medically. One exception is sudden SNHL which may respond to timely steroid treatment. Hearing aids usually benefit patients with SNHL. Patients could also have mixed hearing loss, a hearing loss with both a conductive and sensorineural component (e.g., chronic otitis media coexistent with cochlear damage) ( Fig. 33.1 ).

  

3

What is the Weber tuning fork test? How is it performed and interpreted?

The Weber test is not a test of hearing, but it can provide information about the type of hearing loss. In the Weber test a tuning fork is struck and its base is placed midline on the patient’s forehead. Commonly, a 512 Hz and/or 1024 Hz (hertz or Hz: a unit of measure for cycles per second) tuning fork is used. The patient is first asked where the tone is perceived and next whether the tone is louder in one ear or the other. With CHL, the tone is louder and localizes to the poorer hearing or affected ear. With SNHL, the patient perceives the tone as louder in the better hearing or unaffected ear. Patients with equal hearing or bilaterally symmetric hearing loss will localize the sound to the skull midline.

4

What is the Rinne tuning fork test? How is it performed?

The Rinne test is also used to differentiate between CHL and SNHL. The test is performed by alternately placing the prongs of a vibrating tuning fork at the patient’s ear canal and the base of the tuning fork on the patient’s mastoid bone. The patient is asked whether the tone sounds louder at the ear canal or on the mastoid. In a patient with normal hearing and normal middle ear status, the tuning fork sounds louder at the ear canal or equally loud in both positions. Similar findings are expected in a patient with SNHL. Patients with CHL, however, hear the tuning fork sound louder at the mastoid position (because their bone conduction is better than their air conduction. This is referred to as a negative Rinne test.). A negative result is obtained when the CHL is at least 25 dB hearing level (dB HL).

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Why are tuning fork tests performed?

Tuning fork tests are primarily performed to assist in evaluating the possible type of hearing loss (CHL versus SNHL). They contribute little to evaluating the presence or degree of hearing loss, which should be assessed through a complete audiometric evaluation. However, they can be useful in a situation where the patient would not tolerate complete audiometric testing (e.g., a trauma patient in the ICU) or if audiometry is not available.

6

How wide is the frequency range for normal hearing?

The young human ear can detect sound in the frequency range of 20 to 20,000 Hz. High-frequency hearing tends to deteriorate with age. Audiometric test procedures typically evaluate from 250 to 8000 Hz, due to the range of speech frequencies in spoken language.

7

What is a decibel?

A decibel (dB) is an arbitrary unit of measurement, for the intensity of sound, that is logarithmic in nature. There are several decibel scales used to measure sound intensity and hearing sensitivity, so it is necessary to identify the reference scale, when presenting a value in decibels. For example, hearing is measured on a biologic scale in decibels hearing level (dB HL), whereas environmental sounds are measured on a physical scale in decibels sound pressure level (dB SPL). The normal ear is not equally sensitive to all frequencies, as it is able to hear mid-frequencies better than low and high frequencies. Normal hearing is approximately 45 dB SPL at 125 Hz, 7 dB SPL at 1000 Hz, and 16 dB SPL at 6000 Hz. A reference level of 0 dB HL represents normal hearing across the assessed frequency spectrum.

8

What is an audiogram?

An audiogram is produced using a relative measure of the patient’s hearing, as compared with an established “normal” value ( Fig. 33.2 ). It is a graphic representation of auditory threshold responses that are obtained from testing a patient’s hearing with pure-tone stimuli ( Table 33.1 ). An auditory threshold is defined as the minimum intensity at which a patient perceives a sound stimulus 50% of the time. The parameters of the audiogram are frequency, as measured in cycles per second or hertz (Hz), and intensity, as measured in dB HL. The typical audiogram is determined by establishing hearing thresholds for single-frequency sounds at 250, 500, 1000, 2000, 4000, and 8000 Hz; the primary speech frequencies are 500, 1000, 2000, and 4000 Hz. The interoctave frequencies 3000 and 6000 Hz are also commonly measured.

9

What is normal hearing?

Normal adult hearing is between 0 and 20 dB HL. The measurement of hearing is based on threshold responses, with a threshold defined as the dB HL level at which a patient perceives a sound stimulus 50% of the time. Patients with hearing loss have audiograms with poorer thresholds, >20 dB HL ( Table 33.2 ).

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