Otolaryngologists often rely on audiologic test results to determine the course of treatment for a given patient. Many of the tests constituting the diagnostic audiologic battery of 20 years ago have now been replaced with newer procedures with greater specificity, sensitivity, and site of lesion accuracy. This is exemplified by the fact that the terms “sensory” or “neural” can now frequently replace the term “sensorineural.” In addition, audiologic tests have gone beyond the realm of identifying anomalies in structure to identifying anomalies in function. The logical extension of this advancement is to provide the audiologist and otolaryngologist with information related to prognosis and rehabilitation.
Audiologic tests can be classified according to measures of hearing threshold, suprathreshold recognition of speech, assessment of middle ear function, assessment of cochlear function, determination of neural synchrony and evaluation of vestibular function. The test correlates associated with these measures are pure-tone audiometry, speech recognition, the immittance battery, otoacoustic emissions, electrophysiology, videonystagmography, and rotary chair assessment. The latter two procedures are discussed elsewhere in this textbook.
Audiologic test results should always be interpreted in the context of a battery of tests because no single test can provide a clear picture of a specific patient. In addition, the combination of objective and subjective (behavioral) tests provides a cross-check of the results. There are no age restrictions for audiologic testing; it is now possible and recommended to test newborns within days of birth.
The audiogram is a graph that depicts threshold as a function of frequency. Threshold is defined as the softest intensity level that a pure tone (single frequency) can be detected 50% of the time. Intensity is designated on a normalized decibel hearing level (HL) scale that takes into account the differences in human sensitivity as a function of frequency. The typical range of frequencies tested does not cover the entire range of human hearing (20–20,000 Hz). Instead, the range includes the frequencies considered to be essential for understanding speech (250–8000 Hz). Most testing is administered at discrete octave frequencies. However, when threshold differences between adjacent octaves exceed 15 dB, inter-octave frequencies should be tested. This is particularly true at 3000 and 6000 Hz, where “notches” in audiometric configuration often typify noise-induced hearing loss. Thresholds are measured clinically in 5-dB steps. There is a test-retest variability of ±5 dB. Therefore, a change of 10 dB may not necessarily represent a true threshold shift.
Thresholds can be obtained using air conduction (AC) or bone conduction (BC). Sound transmission via earphones, foam inserts, or loudspeakers requires the movement of air molecules; therefore, it is termed air conduction. This testing assesses the entire auditory system from the outer ear to the auditory cortex. Testing through loudspeakers (sound field) cannot isolate differences between ears. The advantages of insert earphones over over-the-ear (supra-aural) earphones include the prevention of collapsing ear canals, greater attenuation from ambient noise, and greater interaural attenuation (the loss of sound energy ...