33 Evaluation of Hearing Flashcards
What questions do you ask of a patient presenting with hearing loss?
What questions do you ask of a patient presenting with hearing loss?
As with any evaluation, it is important to first obtain a detailed history of the problem. Details such as onset, course since onset, ear(s) involved, excacerbating and relieving factors, and related symptoms are important. Also noted are the presence of tinnitus, vertigo, aural fullness, and ear pain.
A detailed family, medical, and social history, including noise exposure, should be obtained to search for risk factors. Patients also 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.
Describe the two general types of hearing loss. How are they different?
Describe the two general types of hearing loss. How are they different?
- Conductive hearing loss (CHL) results from any 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, foreign bodies, otitis media, or otosclerosis. Conductive losses are often correctable with medical or surgical treatment.
- Sensorineural hearing loss (SNHL) results from otologic abnormalities beyond the oval window. Such abnormalities may affect the sensory cells of the cochlea or the neural fibers of the eighth cranial nerve. Presbycusis, or hearing loss related to aging, is an example of an SNHL. Eighth cranial nerve tumors may also lead to such a loss. Sensorineural losses are generally permanent and are typically unmanagable medically. Hearing aids usually benefit these patients. Patients may also have a mixed hearing loss that combines both CHL and SNHL (e.g., resulting from chronic otitis media coexistent with cochlear damage).
What is the Weber tuning fork test? How is it performed and interpreted?
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 loss. In the Weber test a tuning fork is struck and its base is placed midline on the patient’s skull. Commonly a 512 Hz and/or 1024 Hz (hertz or Hz: a unit of measure for cycles/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. In CHL, the tone is louder and localizes to the poorer hearing or affected ear. In SNHL, the patient perceives the tone to be louder in the better hearing or unaffected ear. Patients with equal hearing or bilaterally symmetric hearing problems will localize the sound to the skull midline.
What is the Rinne tuning fork test? How is it done?
What is the Rinne tuning fork test? How is it done?
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 is heard louder at the ear canal or on the mastoid. In the patient with normal hearing and normal middle ear status, the tuning fork is heard louder at the ear canal or equally loud in both positions. Similar findings are expected from a patient with SNHL. Patients with conductive loss, however, hear the tuning fork sound louder at the mastoid position (a negative Rinne test result, bone conduction is greater than air conduction). A negative test is obtained when the CHL is at least 25 decibels hearing level (dB HL).
Describe the Schwabach’s tuning fork test.
Describe the Schwabach’s tuning fork test.
The Schwabach’s test is a crude comparison of the patient’s hearing to a presumed normal hearing person (the examiner) and does not replace a complete audiometric evaluation. The base of a vibrating tuning fork is placed on the patient’s mastoid bone. When the tone decays to the point that the patient is unable to perceive it, the examiner quickly transfers the tuning fork to his or her own mastoid. If the examiner is able to hear the tone, the test indicates that the patient has an SNHL. The test result is then reported as “diminished,” reflecting the patient’s hearing status. This test, of course, requires that the examiner have normal hearing.
Why are tuning fork tests performed?
Why are tuning fork tests performed?
Tuning fork tests are done to primarily 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 done with 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.
How wide is the frequency range for normal hearing?
How wide is the frequency range for normal hearing?
The human ear can detect sound in the frequency range of 20 to 20,000 Hz. However, the typical adult can only detect frequencies between 200 and 10,000 Hz. The speech frequency spectrum ranges from 400 to 5000 Hz, and audiometric test procedures typically evaluate 250 to 8000 Hz.
What is a decibel?
What is a decibel?
A decibel is an arbitrary unit of measurement that is logarithmic in nature. Several decibel scales are used to measure sounds and hearing, and it is necessary to identify each 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, and it is able to hear mid frequencies better than low and high frequencies. Normal hearing at 125 Hz is about 45 dB SPL, at 1000 Hz is about 7 dB SPL, and at 6000 Hz is about 16 dB SPL. A reference level of 0 dB HL represents normal hearing across the entire frequency spectrum.
What is an audiogram?
What is an audiogram?
An audiogram is produced using a relative measure of the patient’s hearing as compared with an established “normal” value (Figure 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). The parameters of the audiogram are frequency, as measured in cycles per second (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 thresholds are 500, 1000, and 2000 Hz. The interoctaves of 3000 and 6000 Hz are commonly measured as well.
What is normal hearing?
What is normal hearing?
Practically speaking, normal adult hearing is represented as a general range between 0 and 20 dB HL. The measurement of hearing is based on threshold responses, with a threshold defined as that point at which a patient perceives a sound stimulus 50% of the time. Patients with hearing loss have audiograms with poorer thresholds (larger numbers in decibels) at the involved frequencies. This is generally considered to be >20 dB (Table 33-2).
What is the pure-tone average?
What is the pure-tone average?
The pure-tone average (PTA) is an estimate of the patient’s ability to hear within the speech frequencies. The value is calculated by averaging the air conduction hearing thresholds at 500, 1000, and 2000 Hz. For individuals with a precipitously sloping hearing loss, a Fletcher’s average is commonly used, which is the average of the two best thresholds that are typically used to obtain the PTA.
When an audiologist says that a hearing loss requires masking to verify, what does this mean?
When an audiologist says that a hearing loss requires masking to verify, what does this mean?
Loud sounds presented to the test ear can travel via bone conduction through the skull and be perceived in the opposite, nontest ear. This phenomenon, called crossover, can obscure measurement results in the test ear. Therefore, the nontested ear must be excluded from the test. Air conduction sounds can cross over when a difference of as little as 40 dB exists between the air conduction threshold of the test ear and the bone conduction threshold of the nontest ear. This may vary depending on head size and transducer used. Headphone crossover occurs at lower levels (40 to 60 dB) than insert earphones (70 to 90 dB). Bone conduction sounds may cross over when a difference as little as 0 dB exists between the bone conduction thresholds of the two ears. Masking is the simultaneous presentation of sound to the nontest ear while testing the other ear with the stimulus; this serves to prevent the nontest ear from interfering with true sound perception in the test ear.
How does the audiologist distinguish between air and bone conduction deficits?
How does the audiologist distinguish between air and bone conduction deficits?
In measurements of air conduction hearing thresholds, headphones or inserted ear phones deliver sound to the patient. If a hearing loss is noted on testing air conduction, bone conduction hearing thresholds are subsequently performed. Bone conduction is tested by placing a vibrating device (bone oscillator) behind the ear on the mastoid. The bone oscillator presents the sound to the inner ear, thus bypassing the middle ear system. Patients with SNHL have equal hearing thresholds by air and bone conduction measurements. Patients with CHL have normal cochlear function; therefore, they show normal hearing thresholds by bone conduction but poor hearing thresholds by air conduction.
What do you look for on an audiogram to tell whether a hearing loss is sensorineural or conductive?
What do you look for on an audiogram to tell whether a hearing loss is sensorineural or conductive?
Look for an air–bone gap. An air–bone gap is the difference in decibels between the hearing thresholds obtained using the insert earphones (air conduction) and those obtained using the bone oscillator (bone conduction). Significant air–bone gaps represent CHL (Figure 33-3). Because the patient hears better through bone conduction than with insert earphones/headphones, a gap exists between the two measurements. With normal hearing, the air and bone conduction thresholds are approximately equal (≤10 dB difference). With SNHL (Figure 33-4), the air and bone conduction thresholds are approximately equal but, overall, show a deficit (>10 dB). A conductive loss would result in a gap between a more normal bone conduction threshold, and the poorer air conduction threshold.
What is the speech reception threshold (SRT) test?
What is the speech reception threshold (SRT) test?
This test is performed to confirm the pure-tone threshold findings. The patient is familiarized with a specific set of bisyllablic words, known as spondees, which are then presented to the patient at decreasing intensities. Spondees are two-syllable compound words that are pronounced with equal emphasis on each syllable—for example, oatmeal, popcorn, and shipwreck. The SRT is the lowest intensity at which the patient correctly identifies the word in 50% of the presentations. The SRT should typically be within ±7 dB of the three-frequency pure-tone average or, for patients with a precipitously sloping hearing loss, the Fletcher’s average.
The chart of a patient says that she had a type B tympanogram on her last visit. What does this mean?
The chart of a patient says that she had a type B tympanogram on her last visit. What does this mean?
- Type A- Normal middle ear function
- Type As- Tympanic membrane is stiffer than normal (lower compliance), in the presence of normal middle ear pressures (i.e. otosclerosis)
- Type Ad- Tympanic membrane is more flaccid than normal (higher compliance), in the presence of normal middle ear pressures (i.e. ossicle discontinuity)
- Type B- Also known as a flat tympanogram, It shows no peak pressure and indicates nonmobilityof the thmpanic membrane (e.g. middle ear effusion or perforated tympanogram
- Type C- Tympanic membrane shows a peak in the negative pressure range (< -150 mm H2O) ; indicates poor eustacian tube function.
