Response of the cat eardrum to static pressures: mobile versus immobile malleus.
A phase-shift shadow moiré interferometer was used to measure the shape of the cat eardrum with a normal mobile malleus and with an immobile malleus as it was cyclically loaded with static middle-ear pressures up to +/-2.2 kPa. The shape was monitored throughout the loading and unloading phases, and three complete cycles were observed. The mobile-manubrium measurements were made in five ears. In three ears, the malleus was then immobilized with a drop of glue placed on the head of the malleus. Eardrum displacements were calculated by subtracting shape images pixel by pixel. The measurements are presented in the form of gray-level full-field shape and displacement images, of displacement profiles, and of pressure-displacement curves for selected points. Displacement patterns with a mobile malleus show that pars-tensa displacements are larger than manubrial displacements, with the maximum pars-tensa displacement occurring in the posterior region in all cats except one. Displacements vary from cycle to cycle and display hysteresis. For both the mobile-malleus and immobile-malleus cases, the eardrum response is nonlinear. The response is asymmetric, with lateral displacements being larger than medial displacements. With a mobile malleus, manubrial displacements exhibit more pronounced asymmetry than do pars-tensa displacements.
Ladak
Hanif M
HM
Department of BioMedical Engineering, McGill University, Montreal H3A 2B4, Canada. hladak@uwo.ca
Decraemer
Willem F
WF
Dirckx
Joris J J
JJ
Funnell
W Robert J
WR
D000465:Algorithms; D000818:Animals; D002415:Cats; D008307:Malleus / Q000502:physiology*; D015903:Moire Topography; D011312:Pressure; D013997:Time Factors; D014432:Tympanic Membrane / Q000502:physiology*