Sound energy is maximally absorbed into the middle ear and minimally reflected, when the air pressure on both surfaces of the tympanic membrane is equalized. The probe tip tone is directed to the tympanic membrane during the two seconds of the pressure change described above. Normal middle ear pressure should be somewhere between +50 to ≡50 dePa (mm water). When there is a definable tympanometric peak, ie, no middle ear effusion, the location of the peak along the abscissa (x-axis) provides a measure of the pressure in the middle ear. This is the point where the pressure in the middle ear and the pressure in the ear canal are equal. The highest point in the tympanometric pattern on the y-axis is labeled as the tympanometric peak, the point of maximum admittance. Static admittance is measured in mmohs (the reciprocal of milliohms). If the middle ear contains air only, the tympanogram pattern displays air pressure in the abscissa (x-axis) and admittance (previously called compliance) on the ordinate (y-axis). Normally, canal admittance (volume), should range between 0.2 to 1.5 mmohs. One dePa is about equal to 1 mm water pressure.Īt a pressure of +200 dePa, the distance from the x-axis of the graph to the beginning of the tympanogram pattern is called the canal admittance, important because it approximates the volume of air (mmohs) of the ear canal. The pressure pump first introduces positive pressure to +200 dePa (deca-pascals) that is quickly rarefied down to a pressure of ≤00 dePa over a few seconds. This examines the range of mobility of the tympanic membrane under varying pressures, similar to the performance of pneumatic otoscopy.Īt the same time, the sound processor (transducer) continuously emits a pure tone of 226 Hz with an intensity of 85 dB. During the performance of the test, the air pressure in the sealed ear canal is varied by means of an automatic pressure pump. Image courtesy of Brad Ingrao, MSEd, CCC-A, FAAA / EDEN-The Electronic Deaf Education Network / Tympanometry, the older and more widely used technology, is available in one or more models from at least 10 U.S.

Types of tympanograms