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Loose Probe Fit

Source
The information presented here is based on clinical examples as well as modeled patterns. Text and accompanying. Absorbance sketch is authored by Navid Shahnaz, PhD, Aud, Associate Professor of Audiology in the School of Audiology & Speech Sciences at the University of British Columbia (UBC).

Note
Absorbance measures under more or less blocked conditions will vary. The displayed Absorbance pattern is a sketched example only.

Absorbance characteristics to look for:
The condition obviously has great variability due to the many ways the probe can be loosely fit. In general, the Absorbance will be at an unusually high level at frequencies below 2 kHz, and the pattern might be jerky.

Sketched example of absorbance pattern
Sketched example

Consequences of probe fit
All Absorbance measures need to have a good probe fit to be reliable. Evaluating Absorbance as provided by the 3D Tympanometry test ensures that a reasonably air tight probe seal was accomplished, as the air pressure sweep would not have been performed otherwise. In addition to an air tight probe seal, a deeper rather than a shallower probe insertion ensures the most accurate Absorbance measures. Shallow insertions tend to provide more elevated Absorbance readings at lower frequencies. This is somewhat similar to normal Tympanometry measures that are also influenced by probe fit and probe insertion depth.

Suggested reading
Effects of Middle-Ear Disorders on Power Reflectance Measured in Cadaveric Ear Canals, Voss, Susan E., Merchant, Gabrielle R.,Horton, Nicholas J., Ear & Hearing. 33(2):195-208, March/April 2012.

Acoustic Immittance Measures, Basic and Advanced Practice, 2013, Lisa Hunter, Phd, FAAA, Navid Shahnaz, PhD, Aud. (C), Plural Publishing. ISBN10: 1-59756-437-0, ISBN13: 978-1-59756-437-3.

May 2015
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