Computers may be programmed to control all aspects of administering pure-tone air- and bone-conduction stimuli, recognize the need for masking, determine the appropriate level of masking, regulate the presentation of the masker to the nontest ear, analyze the subject’s responses in terms of threshold-determination criteria, and present the obtained threshold values in an audiogram format at the conclusion of the test. Computerized audiometry is performed on a device that is
12. Severe
microprocessor controlled, and the audiometric data may be “dumped” into a computer file for later retrieval.
Possibly due to economic considerations, several companies have been formed that spe-cialize in hearing testing performed by nonaudiologists, sometimes called para-audiologists or oto-techs. These individuals, many of whom have no academic training in hearing and its disorders, are trained to use automated devices that are programmed to complete pure-tone audiometry, and speech audiometry (Chapter 5), as well as immittance measures (Chapter 7), in a matter of 20 minutes. The claims by these firms are that the results are reliable, but this has not been empirically verified. Certainly automated audiometry cannot be used reliably with noncooperative patients (Chapter 13) or with young children or the very elderly who may need more personalized modifications in test procedure and speed to accommodate the test situation.
Presumably, in these computerized hearing settings physicians carry out the counseling and follow-up. This leaves the patients without the special training of clinical audiologists in the areas of counseling, therapy, and amplification systems. Despite its sophistication, the computer has not replaced, nor is it likely to replace, the clinical audiologist in the performance of audi-tory tests outside of its possible use with test-cooperative patients. The fact that computers can make step-by-step decisions in testing helps to prove that many hearing tests can be carried out logically and scientifically.
E VO LV I N G C A S E S T U D I E S
You were introduced to four theoretical case studies in Chapter 2. The next step is to predict, based on your reading of Chapter 4, what the pure-tone audiometric results would be for each of these cases. Sketch an audiogram for each case and compare your results to the discussion below, bearing in mind that there will naturally be some differences.
Case Study 1: Conductive Hearing Loss
Audiometric findings for this patient should be similar to what is observed in Figure 4.13.
Note that there is a mild-to-moderate hearing loss by air conduction for both ears (the pure-tone averages are 35 dB HL) but that the bone-conduction thresholds are normal, indicating normal sensory/neural sensitivity. The resultant air-bone gaps show the degree of conductive involvement. These results do not indicate the etiology (cause) of the hearing loss or the part of the auditory system that is involved, but the tests described in later chapters will assist in this regard. The history of ear infections suggests this as the etiology but may be misleading.
Case Study 2: Sensory/Neural Hearing Loss
Compare the audiogram you have drawn to Figure 4.14. Results should be similar but surely will not be identical. You should have shown a moderate loss, in this case approximately 45 dB based upon the variable pure-tone average (poorest three thresh-olds for 500, 1000, 2000, and 4000 Hz), but the air-conduction and bone-conduction thresholds should be about the same.The lack of an air-bone gap indicates that the loss is entirely sensory/neural. The case history points to aging as the etiology but further tests, as described in later chapters, can help to determine the site of the pathology.
98 C H A P T E R 4 Pure-Tone Audiometry
REVIEW TABLE 4.1 Summary of Pure-Tone Hearing Tests
(Minimal interaural attenuation is considered to be 40 dB for supra-aural earphones and 70 dB for insert earphones.)
Test Air Conduction (AC) Bone Conduction (BC)
Purpose Hearing sensitivity for pure tones Sensory/neural sensitivity for pure tones Interpretation AC audiogram shows amount
of hearing loss at each frequency
BC audiogram shows degree of sensory/neural loss at each frequency Air-bone gap shows amount of conductive impairment at each frequency
Case Study 3: Erroneous Hearing Loss
There is no audiogram in Chapter 4 to illustrate this case since your patient appears to be pretending to have no hearing in his left ear. What you may have drawn should closely resemble Figure 13.2A. He is reporting normal hearing in his right ear and gives no response by either air conduction or bone conduction at the highest inten-sities in his left ear. This is actually impossible because at some intensity (possibly as low as 40 dB HL for supra-aural earphones and 70 dB HL for insert earphones) the sound would have lateralized (crossed the skull) and been heard in the right ear. This total lack of response is a clear indication that the hearing loss in the left ear cannot be of the degree claimed, but based on the present information it cannot be learned just how much loss exists in the left ear, if any. Chapter 5 will allow for more insights about this case, and Chapter 13 will describe tests that are specific to erroneous hear-ing loss.
Case Study 4: Pediatric Patient
The test procedures described in Chapter 4 are designed for adults and older children, or young children who are particularly cooperative. There are some youngsters who can take adult-level tests that have been modified by an audiologist who provides significant social reward for accurate responses. Unfortunately, this child is not in this category and so you are referred to Chapter 8 to learn about procedures specifically designed for pediatric patients.
Summary
For pure-tone hearing tests to be performed satisfactorily, control is needed over such factors as background noise levels, equipment calibration, patient comprehension, and clinician expertise.
The audiologist must be able to judge when responses are accurate, and to predict when a sound may have actually been heard in the ear not being tested. When this cross hearing occurs, proper masking procedures must be instituted to overcome this problem as discussed in Chapter 6.
Although at times the performance of pure-tone hearing tests is carried out as an art, it should, in most cases, be approached in a scientific manner using rigid controls.
REVIEW TABLE 4.2 Possible Findings for Air Conduction (AC) and Bone Conduction (BC)
Finding Possibilities Eliminate
Normal AC Normal hearing Conductive loss
Sensory/neural loss
1. Sketch an audiogram from memory. What is the proportional relationship between hearing level and the octave scale? Why?
2. Draw audiograms from memory illustrating normal hear-ing, conductive hearing loss, sensory/neural hearing loss, and mixed hearing loss. What would the results for these hypothetical patients be on the tuning-fork tests described in Chapter 2?
3. Name the parts of a pure-tone audiometer.
4. How would you calibrate an audiometer for air conduction and bone conduction, both with and without electroacoustic equipment?
5. What are the advantages and disadvantages of insert receivers for air-conduction testing?
6. List the advantages and disadvantages of testing bone con-duction from the forehead and the mastoid.
7. Describe the audiometric Weber test. What possible hear-ing losses might yield a lateralization to the right ear? When might you employ this test?
Endnotes
1. The term “audiometer” was first coined by an English physi-cian, Benjamin Richardson, in 1879. It was not until 1919 that the first clinically useful audiometer, the Pitch Range Audiometer, was developed by Lee Dean and Cordia Bunch.
2. This test was suggested by Dr. Georg von Békésy, the Hungarian-born physicist (1899–1976) who won the Nobel Prize in 1961 for his contributions to the understanding of the human cochlea.
Suggested Readings
Bankaitis, A. U., & Kemp, R. J. (2003). Infection control in the audiology clinic. Boulder, CO: Auban.
Schlauck, R. S., & Nelson, P. (2009). Puretone evaluation. In J. Katz, L. Medwetsky, R. Burkhard, & L. Hood (Eds.), Handbook of
clinical audiology (pp. 30–49). Baltimore: Lippincott Williams
& Wilkins.
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