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P-E tubes and TEOAEs ???

Kelley Mascher mascher at u.washington.edu
Thu Jul 27 11:12:48 EST 1995


All of your suppositions about P-E tubes match with what we have
seen in clinical data. As far as I know there haven't been any 
studies on TEOAEs and tubes, but I may have missed something.

The main thing to look for in evaluating TEOAEs with tubes is 
stimulus ringing. This is caused by the increased ear canal volume
due to the tube ( outer ear, middle ear volumes coupled ) requiring
more power to be delivered by the driver to reach the desired
stimulus level. Also keep an eye on the gain parameter. If gain
is high you will have a better chance of overdriving the driver
causing ringing.

When the volume of the earcanal is increased there is a problem
not only with providing enough undistorted stimulus, but also 
with the response. Measuring an OAE response depends on the 
response being able to pressurize the ear canal air mass. If 
the ear canal volume is too large the OAE appears small. This
is why OAE measurments always require the best seal possible.
If the PE tubes increase the ear canal volume the OAE response
will appear to be smaller.

We have seen great variability in responses with tubes. My guess
is that this is due more to the variation in the tube function
( how well it couples the outer/middle ear volumes ) than to the 
variation in the real responses of the individuals involved.

As a disclaimer, I think the physics of this explaination is sound.
The data is just what has been passed in front of me from the 
clinic so it is somewhat anecdotal.

Kelley 

chfseat at aol.com (Chf seat) writes:

>Does anyone have any information on the effect, if any, of patent p-e
>tubes on the measurement of transient evoked emissions ??? it would seem
>that there may be an effect on the transfer function of the middle ear
>system by mass-loading. also, it seems possible that depending on the
>placement of the tube, there could be cancellation via acoustic energy
>falling on the round window. What are the implications for testing
>cochlear function in hard to test children with possible mixed hearing
>losses.  Often, with negative middle ear pressure and/or effusion, the ABR
>results are affected and emissions are obscured. With placement of tubes,
>can be expect a valid test???
-- 
Kelley Mascher                                            (206) 528-2713
Children's Hospital & Med. Center               mascher at u.washington.edu
Audiology Research



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