A new structural model is described for the tension-radius relationship of blood vessels, taking into account their mechanically important constituents: collagen, elastin and smooth muscle. The model has four characteristic parameters: EC, the Young's modulus of the collagen fibres; ESE, the Young's modulus of the combined smooth-muscle/elastin network; epsilon mu, the amount of strain at which the high stiffness region on the tension-radius curve is reached, and eta an indicator for the degree of collagen fibre stretching. The structural stiffness of the wall constituents is reflected by EC and ESE whereas the global stiffness of the entire blood vessel is described by epsilon mu and eta. All these elasticity parameters are pressure independent, in contrast to generally quoted values for the incremental modulus or vascular compliance which are strongly pressure dependent. Hence, an objective comparison of the mechanical properties for various types of blood vessel, based on the present model parameters, has been made possible. The model was successfully fitted to tension-radius data of 65 human aortas, age range 30-88 years, with moderate or severe atherosclerosis. The structural as well as the global stiffness changes with age, e.g. collagen stiffness shows a ninefold increase over 60 years. Global stiffness depends on atherosclerosis.

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Recent measurements of three-dimensional stapes motion in gerbil indicated that the piston component of stapes motion was the primary contributor to intracochlear pressure. In order to make a detailed correlation between stapes piston motion and intracochlear pressure behind the stapes, simultaneous pressure and motion measurements were undertaken. We found that the scala vestibuli pressure followed the piston component of the stapes velocity with high fidelity, reinforcing our previous finding that the piston motion of the stapes was the main stimulus to the cochlea. The present data allowed us to calculate cochlear input impedance and power flow into the cochlea. Both the amplitude and phase of the impedance were quite flat with frequency from 3 kHz to at least 30 kHz, with a phase that was primarily resistive. With constant stimulus pressure in the ear canal the intracochlear pressure at the stapes has been previously shown to be approximately flat with frequency through a wide range, and coupling that result with the present findings indicates that the power that flows into the cochlea is quite flat from about 3 to 30 kHz. The observed wide-band intracochlear pressure and power flow are consistent with the wide-band audiogram of the gerbil. Keywords: middle ear, cochlea, stapes, powerAbbreviations: SV -scala vestibuli; EC -ear canal; PF -pars flaccida; LPI -long process of the incus; PLP -plate of the lenticular process of the incus; CAPcompound action potential; SPL -sound pressure level; CT -computed tomography; BM -basilar membrane; BF -best frequency; TM -tympanic membrane; PUR -power utilization ratio; MEE -middle ear efficiency List of Symbols: U s -stapes volume velocity (mm 3 /s); V s -stapes velocity (mm/s); A fp -effective footplate area (mm 2 ); Z c -cochlear input impedance; Z Eradiation impedance looking out the external ear from the TM; Z T -middle ear input impedance (Pa s/m 3 = N s/m 5 ); P -Power; P ME -middle ear power (W); P sv -SV pressure; P EC -EC pressure (Pa)

This article presents frequency responses calculated using a three-dimensional finite-element model of the cat eardrum that includes damping. The damping is represented by both mass-proportional and stiffness-proportional terms. With light damping, the frequency responses of points on the eardrum away from the manubrium display numerous narrow minima and maxima, the frequencies and amplitudes of which are different for different positions on the eardrum. The frequency response on the manubrium is smoother than that on the eardrum away from the manubrium. Increasing the degree of damping smooths the frequency responses both on the manubrium and on the eardrum away from the manubrium. The overall displacement magnitudes are not significantly reduced even when the damping is heavy enough to smooth out all but the largest variations. Experimentally observed frequency responses of the cat eardrum are presented for comparison with the model results.