Experimental And Modelling Study Of Gerbil Middle Ear

Author : Orhun Kose
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (134 download)

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Download or read book Vibrations of the Gerbil Middle Ear Under Quasi-static Pressures written by Orhun Kose and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Tympanometry is a clinical test that records the response of the ear to sound during large air-pressure sweeps, to determine the status of the external and middle ear. The acoustical and mechanical response of the ear during this test is not well understood. To help improve our understanding, in this thesis we investigate the effects of quasi-static pressures on vibrations of the gerbil eardrum. Using a single-point laser Doppler vibrometer (LDV), the vibration magnitudes at several locations on the eardrum were measured. A pressurization cycle included decreasing the middle-ear pressure from 0 Pa to −2500 Pa, increasing it back to 0 Pa, increasing it to +2500 Pa, and then decreasing it back to 0 Pa. The acoustic input was a linear chirp ranging from 0.5 to 10 kHz. The first experimental study used a step-wise pressurization protocol in which the pressure was changed in 500-Pa increments and held constant for 10 s at each step. The low-frequency vibration magnitude decreased for both negative and positive pressures, with larger changes at smaller pressures; the magnitudes were smaller for negative middle-ear pressures than for the corresponding positive ones. At zero middle-ear pressure, as the frequency increased the vibration magnitude initially increased slightly up to a broad peak (R1), but as the pressure was made more negative the low-frequency vibration magnitude became constant with frequency and later decreased with frequency, and R1 shifted to slightly higher frequencies. R1 was visible at all locations for small pressures, and on the manubrium it was also visible for larger negative pressures. There was a magnitude dip around −1000 to −1500 Pa. A higher-frequency peak (R2) shifted gradually for large pressures, and was visible at all locations; it was seen as a cluster of peaks on the pars tensa. A small low-frequency peak at about 0.7 kHz was only visible on the pars flaccida. The overall vibration magnitude at the umbo was slightly higher than at mid-manubrium. The largest vibration magnitudes were observed on the posterior pars tensa. The frequency response on the pars flaccida was smooth near ambient pressure, similar to that at the umbo, but it changed rapidly when pressurized, already displaying a series of pronounced peaks and troughs by ±500 Pa.The second experimental study used a continuous pressure sweep instead of steps, with the same overall cycle duration as in the first study. The response behaviours were similar to those seen for pressure steps but many more details could be observed. For example, the magnitude dip started near R2 and then expanded quickly to frequencies below that peak. A trough on the posterior pars tensa, which shifted in a way similar to R2, appeared as a peak on the anterior pars tensa.A previous finite-element model, which simulated responses to both sounds and large quasi-static pressures, was further developed to accommodate both pressure steps and pressure sweeps. The simulation results were compared with our data and with data from other groups. The model replicates some of the experimentally observed behaviours but there are some discrepancies. Collectively these experimental and modelling studies will ultimately lead to being able to extract more information from tympanometry and thus to improvements in clinical decision making"--