Norm of Acoustic Immittance Tests
Normal acoustic immittance.
Tympanogram of Acoustic Immittance Tests
The tympanogram recording shows a symmetric, shallow upslope and downslope free of notches or peaks with middle ear pressure of -100 to +100 dPa.
Pure-Tone Reflex Threshold:
|70–100 dB HL|
|3–12 dB HL|
|< ½ baseline/10 seconds|
Usage of Acoustic Immittance Tests
Assessment of middle ear and tympanic membrane functioning; identification of location of middle ear lesions; and differential diagnosis of brainstem lesions and hearing loss; evaluation of tinnitus or vertigo; and evaluation of Bell's palsy.
Description of Acoustic Immittance Tests
The acoustic immittance tests measure middle ear functioning and locate abnormalities by tympanometry and measurement of acoustic reflexes and static acoustic impedence. Tympanometry assesses stiffness of the middle ear by measuring admittance (that is, how much impedance exists to the flow of sound into the ear). Lower than normal admittance can be caused by cerumen, the presence of fluid in the middle ear, or a perforated tympanic membrane. Higher than normal admittance results when ear scarring is present. Measurement of acoustic reflexes shows how well the stapedius muscle responds to the delivery of sound against it. Poor or no acoustic reflexes can indicate hearing loss, neurologic or stapedius muscle damage or lesions, otosclerosis, or absence of the stapes.
Professional Considerations of Acoustic Immittance Tests
Consent form NOT required.
May be contraindicated in clients with accidental head injuries or suspected labyrinthine fistula or in those who have recently undergone ear surgery.
- Obtain admittance meter; recorder; probe with tips, cuffs, and silicone putty; otoscope; and audiometer.
- See Client and Family Teaching.
- Cleanse the bores of the ear probe with wire. Calibrate the admittance meter. Inspect the ear canal, and remove any impacted cerumen.
- Lift the auricle up and out, and insert the admittance meter's cuffed probe into the external auditory canal until a pressure of -200 dPa is achieved, indicating an adequate seal.
- Admittance measurement: Admittance recordings are made in response to air-pressure changes made by the meter.
- Acoustic reflex measurement: Measure acoustic reflexes when a 500- to 4000-Hz tone is sent into either ear. Perform ipsilateral measurement in the stimulated ear. You may perform contralateral (transbrainstem) measurement by sending the tone into the opposite ear.
- Reflex-threshold measurement: Measure the reflex threshold by sending progressively louder tones into the ear in 10-dB increments until a reflex occurs and then decreasing the decibels in smaller steps until the lowest level that elicits a reflex is identified.
- Reflex-decay measurement: Measure the reflex decay by sending a 10-second tone equal to the reflex threshold plus 10 dB into the contralateral ear and comparing the degree of initial, 5-second, and 10-second reflexes.
- Cleanse the ear probe.
Client and Family Teaching
- Avoid moving, talking, or swallowing during the test. The test involves transmitting loud tones into the ear, which may be uncomfortable but will not damage the ear.
Factors That Affect Results
- The most accurate results are obtained when the air seal remains continuous. Silicone putty may be used around the circumference of the canal to help maintain the seal.
- Cerumen or silicone putty clogging the probe may cause the tympanogram to show as a flat waveform.
- Incidence of hearing loss is 46% for persons more than 66 years of age, is greater in males than in females, and increases with age.