|1997, 192, Session F8, Poster|
|Vibrations of the cat tympanic membrane measured with high spatial resolution|
|*W.F. Decraemer (University of Antwerp, Antwerpen, Belgium); S.M. Khanna (Columbia University, New York, NY, USA); W.R.J. Funnell (McGill University, Montreal, Canada)|
The vibrations of the tympanic membrane (TM) have been measured in the past with a variety of techniques. Most of these techniques required enhancement of the natural reflectivity of the TM. The spatial resolution of these experiments was limited by the placement of the reflecting objects on the TM. The holographic techniques with higher spatial resolution did not provide phase information, as a consequence the details of TM vibrations were limited to frequencies below a few kHz. At the lowest frequencies points on the TM vibrate in phase and the manubrium moves with an amplitude that is smaller than neighboring points on the anterior and posterior region of the TM. At higher frequencies (above 2.5 kHz) the vibration pattern breaks up in smaller zones.
In our present study we obtain detailed measurements of the modes of TM vibrations. Improved sensitivity of our measuring apparatus allows us to measure vibrations using the natural reflectivity of the TM. Small spot size of the measuring beam provides high spatial resolution. Vibrations were measured with a laser interferometer by viewing through the external earcanal, in response to pure tone acoustical stimulation over a wide frequency range (0.2 to 23 kHz). The xyz-coordinates of the observation points were precisely recorded. The viewing angle was kept constant and measurements performed along cross sections perpendicular to the manubrium in steps as small as 56 microns. Animations of the membrane vibrations in the cross section show that nodal points are seen only at a few frequencies; mostly maxima and minima shift in position during the cycle. Consequently phase varies continuously from one place to the other. The motion of the sections of the TM looks more like a traveling wave rather than a standing wave.