Immittance testing measures the functional integrity of the eardrum and middle ear anatomy. These measures are sensitive to middle ear disorders (such as a hole in the eardrum or fluid in the middle ear space). Immittance testing does not require any behavioral response from the patient.
The test consists of three parts: tympanometry, acoustic reflex testing, and acoustic decay. For tympanometry, a probe tip is placed in one ear and the air pressure in the canal is varied above and below the atmospheric level. Changes in air pressure cause the eardrum, middle ear bones, and associated muscles to react in specific ways. Following tympanometry, the probe will present a series of loud level tones in order to excite a reflex of the stapedial muscle. In a typically functioning ear system, reflexes can be recorded for a variety of different frequency stimuli. Acoustic reflex decay is used for patients in which retrocochlear involvement is suspected. For acoustic reflex decay, a loud level tone is presented to the ear for approximately 10 seconds and a reflex of the middle ear is monitored. The results of these tests are recorded by the computer and provide insight into the function of the middle ear system.