Nima Maftoon

A new approach for the evaluation of the severity of coarctation of the aorta using Doppler velocity index and effective orifice area: In vitro validation and clinical implications

Early detection and accurate estimation of COA severity are the most important predictors of successful long-term outcome. However, current clinical parameters used for the evaluation of the severity of COA have several limitations and are flow dependent. The objectives of this study are to evaluate the limitations of current existing parameters for the evaluation of the severity of coarctation of the aorta (COA) and suggest two new parameters: COA Doppler velocity index and COA effective orifice area. Three different severities of COAs were tested in a mock flow circulation model under various flow conditions and in the presence of normal and stenotic aortic valves. Catheter trans-COA pressure gradients and Doppler echocardiographic trans-COA pressure gradients were evaluated. COA Doppler velocity index was defined as the ratio of pre-COA to post-COA peak velocities measured by Doppler echocardiography. COA Doppler effective orifice area was determined using continuity equation. The results show that peak-to-peak trans-COA pressure gradient significantly increased with flow rate (from 83% to 85%). Peak Doppler pressure gradient also significantly increased with flow rate (80-85%). A stenotic or bicuspid aortic valve increased peak Doppler pressure gradient by 20-50% for a COA severity of 75%. Both COA Doppler velocity index and COA effective orifice area did not demonstrate significant flow dependence or dependence upon aortic valve condition. As a conclusion, COA Doppler velocity index and COA effective orifice area are flow independent and do not depend on aortic valve conditions. They can, then, more accurately predict the severity of COA.

Modeling of Middle Ear Mechanics

Quantitative understanding of the mechanical behavior of the external and middle ear is important, not only in the quest for improved diagnosis and treatment of conductive hearing loss but also in relation to other aspects of hearing that depend on the conductive pathways. Mathematical modeling is useful in arriving at that understanding. This chapter starts with some background modeling topics: the modeling of three-dimensional geometry and of material properties and the verification and validation of models, including uncertainty analysis and parameter fitting. The remainder of the chapter discusses models that have been presented for the external ear canal, middle ear air cavities, eardrum, ossicular chain, and cochlea. The treatment deals mainly with circuit models and finite-element models and to a lesser extent with two-port, rigid-body, and analytical models. Nonlinear models are discussed briefly. The chapter ends by briefly discussing the application of modeling to pathological conditions, some open questions in middle ear modeling, and the disadvantages and advantages of the finite-element method.

Finite-element modelling of the newborn ear canal and middle ear

Available hearing-screening procedures cannot distinguish clearly between conductive and sensorineural hearing loss in newborns, and the results of available diagnostic tests in very young infants are difficult to interpret. Admittance measurements can help to detect conductive losses but do not provide reliable results for newborns, where the ear is anatomically different from the adult ear. Finite-element models of the newborn ear canal and middle ear were developed and their responses were studied for frequencies up to 2000 Hz. Material properties were taken from previous measurements and estimates, and the sensitivities of the models to these different parameters were examined. The simulation results were validated through comparison with previous experimental measurements. Simulations indicate that at frequencies up to 250 Hz the admittance of the canal wall is comparable to that of the middle ear in the newborn. Above 250 Hz, the canal-wall admittance remains almost constant but for the middle ear t...

High-Speed Shape and Transient Response Measurements of Tympanic Membrane

We are developing a High-speed Digital Holographic (HDH) system to measure acoustically induced transient displacements of live mammalian Tympanic Membranes (TM) for research and clinical applications. To date, the HDH can measure one-dimensional displacements along a single 1-D sensitivity vector. However, because of the TM’s tent-like shape and angled orientation inside the ear canal, 1-D measurements need to be combined with measurements of the shape and orientation of the TM to determine the true surface normal (out-of-plane) displacements. Furthermore, TM shape also provides invaluable information for better diagnostic and modelling of the TM. To introduce shape measurements capabilities into our HDH, a tunable laser (line width 67 kHz temporal and <15 nm displacement resolutions) in response to broadband acoustic click excitations (50 μs duration). Both shape and displacement can be measured in less than 150 ms, which avoids slow disturbances introduced by breathing and heartbeat, with the promise of future measurements in vivo. Representative shape and displacement measurements capabilities are demonstrated on cadaveric human temporal bones.

Motion of intracochlear structures measured with a commercial optical coherence tomography (OCT) system

Most knowledge of the motion of cochlear structures has been limited to measurements through the round window at the extreme base of the cochlea or through a hole made in the cochlear capsule, which can modify cochlear mechanics. Optical coherence tomography (OCT) provides the ability to measure shape or motion of structures through a thin layer of tissue or bone. The motion of cochlear structures has been measured in the mouse cochlear apex without making an opening into the cochlea, using a custom OCT system. Here we describe intracochlear vibrometry using a commercial OCT system. Specimens were prepared by opening the middle ear while maintaining part of the cartilaginous ear canal. A Thorlabs 905nm Ganymede III-HR OCT system with 100-kHz camera frame rate was used to measure cochlear anatomy in a 2-D radial slice (B-scan) and dynamic displacements along a line (A-line) that intersected several cochlear structures in response to tones presented to the ear canal. Differences in the magnitude and phase o...

Non-invasive determination of transcatheter pressure gradient in stenotic aortic valves: An analytical model

Aortic stenosis (AS), in which the opening of the aortic valve is narrowed, is the most common valvular heart disease. Cardiac catheterization is considered the reference standard for definitive evaluation of AS severity, based on instantaneous systolic value of transvalvular pressure gradient (TPG). However, using invasive cardiac catheterization might carry high risks knowing that undergoing multiple cardiac catheterizations for follow-up in patients with AS is common. The objective of this study was to suggest an analytical description of the AS that estimates TPG without a need for high risk invasive data collection. For this purpose, Navier-Stokes equation coupled with the elastic-deformation equation was solved analytically. The estimated TPG resulted from the suggested analytical description was validated against published in vivo and in vitro measurement data. Very good concordances were found between TPG obtained from the analytical formulation and in vivo (maximum root mean square error: 3.8 mmHg) and in vitro (maximum root mean square error: 9.4 mmHg). The analytical description can be integrated to non-invasive imaging modalities to estimate AS severity as an alternative to cardiac catheterization to help preventing its risks in patients with AS.

Estimation of ideal open-cavity middle-ear responses from responses with partial cavity opening

An important step in developing mathematical models of the middle ear is the validation of simplified models without the middle-ear air cavity. However, open-cavity experimental results are often collected with only a partial opening of the middle-ear cavity, due to experimental limitations. The partial opening introduces a relatively sharp minimum that obscures features of the frequency response in its neighbourhood. In this study we suggest a numerical method for estimating ideal open-cavity responses from experimental results with partial openings. We fit rational-fraction polynomials to portions of the response in order to parametrically identify the transfer function associated with the sharp minimum. The ideal open-cavity response is then estimated by dividing the experimentally measured frequency response by the identified anti-resonance transfer function. The method has been validated against synthesized transfer functions with features similar to those caused by partial opening of the cavity and ...

An Analytical Model of the Instantaneous Transvalvular Pressure Gradient Through an Aortic Stenosis

Diagnosis and treatment of aortic stenosis largely depends on accurate determination of the pressure difference before and after the valve, known as transvalvular pressure gradient (TPG). Clinically, TPG is obtained using Doppler echocardiography though sometimes invasive cardiac catheterization has to be used to confirm Doppler echocardiography findings. By solving analytically coupled fluid and solid domain equations, we suggest a formulation that with a good degree of accuracy can be used to calculate TPG. Analytical result is validated using experimental data from literature. The suggested methodology is an alternative to cardiac catheterization and helps to prevent its risks.Copyright