Tuning Forks

The 512-Hz tuning fork is the most accepted frequency for assessing hearing using the Weber and Rinne tests. The Weber test consists of placing the stem of a vibrating fork on the center of the patient's forehead, crown, or nasal bridge. Sound is transmitted equally into each cochlea by bone conduction. While the fork is vibrating, ask the patient in which ear the sound is louder. A patient with a one-sided sensorineural loss will hear the fork louder in the opposite, normal ear. A patient with a conductive loss will hear it louder on the problem side, due to the autophony phenomenon (see Chapter 1). Remember, however, that the test only applies to the frequency used, in this case 512 Hz. For example, a patient with a one-sided sensorineural loss in the higher frequencies will still have a normal midline Weber test with a 512-Hz fork if there is no damage at this frequency.

The Rinne test, modified here for simplicity, is a quick way to screen one ear for conductive (outer or middle ear) hearing loss. Place the stem of the vibrating tuning fork on the patient's mastoid bone for a few seconds, then hold the still-vibrating forked portion about 10 cm from the patient's external ear. Ask, "Is it louder on the bone or out here in the air?" A patient with normal hearing (or a sensorineural loss) will note louder hearing "out in the air," rather than "on the bone." On the other hand, a patient with a significant conductive loss (25 dB HL or more) will hear the fork louder on the bone than in the air. If you have a tuning fork available, try this on your own right ear with the canal open; the Rinne should be "normal." Now occlude your canal tightly with the left index finger, creating a conductive loss, and test again; the Rinne should be "abnormal" or "reversed." Using

Basic Equipment 9

the terms "positive" and "negative" is often recommended, but these can be ambiguous. Documenting "air conduction is greater than bone" (or vice-versa) leaves the least room for doubt.

Tuning forks of256,1024, and 2048 Hz are also available and can be useful in many ways. For example, most conductive losses are severest in the lower frequencies. The 256-Hz fork may pick up abnormalities that the 512-Hz one would miss; thus it is the most sensitive one for conductive losses, especially when using the Rinne test. All the frequencies can be used to compare a patient's right ear to his/her left ear, or to the examiner's ear, for rough assessment. Individuals with advanced high-frequency loss from either noise damage or aging may show impairment at 1024 or 2048 Hz.

Other simple assessments can be made. The light rubbing of dry fingers is in the 3000 Hz range, as is the ticking of a watch. The sound intensity, when near the ear, is probably 25 dB HL or less. These are rudimentary but valuable screenings for high-frequency loss.

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