Two passive mechanical conditions modulate power generation by the outer hair cells.

In the mammalian cochlea, small vibrations of the sensory epithelium are amplified due to active electro-mechanical feedback of the outer hair cells. The level of amplification is greater in the base than in the apex of the cochlea. Theoretical studies have used longitudinally varying active feedback properties to reproduce the location-dependent amplification.

Consequences of Location-Dependent Organ of Corti Micro-Mechanics.

The cochlea performs frequency analysis and amplification of sounds. The graded stiffness of the basilar membrane along the cochlear length underlies the frequency-location relationship of the mammalian cochlea. The somatic motility of outer hair cell is central for cochlear amplification.

Two-compartment passive frequency domain cochlea model allowing independent fluid coupling to the tectorial and basilar membranes.

The cochlea is a spiral-shaped, liquid-filled organ in the inner ear that converts sound with high frequency selectivity over a wide pressure range to neurological signals that are eventually interpreted by the brain. The cochlear partition, consisting of the organ of Corti supported below by the basilar membrane and attached above to the tectorial membrane, plays a major role in the frequency analysis. In early fluid-structure interaction models of the cochlea, the mechanics of the cochlear partition were approximated by a series of single-degree-of-freedom systems representing the distributed stiffness and mass of the basilar membrane.

Shear strain from irrotational tissue displacements near bubbles.

Particle displacements can be much greater near bubbles than they would be in a homogeneous liquid or tissue when exposed to an acoustic wave. In a plane wave, shear and bulk strains are of the same order of magnitude. In contrast, for a bubble oscillating close to its resonance frequency, the shear strain in the medium near the bubble is roughly four orders of magnitude greater than the bulk strain.

Natural frequency of a gas bubble in a tube: experimental and simulation results.

Use of ultrasonically excited microbubbles within blood vessels has been proposed for a variety of clinical applications. In this paper, an axisymmetric coupled boundary element and finite element code and experiments have been used to investigate the effects of a surrounding tube on a bubble's response to acoustic excitation. A balloon model allowed measurement of spherical gas bubble response.

Ultrasonic excitation of a bubble inside a deformable tube: implications for ultrasonically induced hemorrhage.

Various independent investigations indicate that the presence of microbubbles within blood vessels may increase the likelihood of ultrasound-induced hemorrhage. To explore potential damage mechanisms, an axisymmetric coupled finite element and boundary element code was developed and employed to simulate the response of an acoustically excited bubble centered within a deformable tube. As expected, the tube mitigates the expansion of the bubble.

Ultrasonic excitation of a bubble near a rigid or deformable sphere: implications for ultrasonically induced hemolysis.

A number of independent studies have reported increased ultrasound bioeffects, such as hemolysis and hemorrhage, when ultrasound contrast agents are present. To better understand the role of cavitation in these bioeffects, one- and two-dimensional models have been developed to investigate the interactions between ultrasonically excited bubbles and model "cells." First, a simple one-dimensional model based on the Rayleigh-Plesset equation was developed to estimate upper bounds for strain, strain rate, and areal expansion of a simulated red blood cell.