MECHANICAL PROPERTIES OF HUMAN INCUDOSTAPEDIAL JOINT AND TYMPANIC MEMBRANE IN NORMAL AND BLAST-DAMAGED EARS

The human ear consists of outer ear, middle ear and inner ear. The mechanical properties of the incudostapedial joint (ISJ) and tympanic membrane (TM) are critical to the sound transmission function of the ear because the transformation of the acoustic pressure to the mechanical vibration relies on the TM while the vibration of the ossicles transmits through ISJ into the cochlea. However, the dynamic properties of ISJ have not been reported in previous studies. Moreover, injuries in the TM and ISJ have been observed in ears exposed to blast overpressure. The structural and functional changes in the ISJ and TM during and after blast exposure were not investigated. In addition, the sound transfer function of the middle ear has not been characterized under blast overpressure. The absence of these mechanical properties and data obtained from function tests of the human ear impedes the improvement of the accuracy of the finite element (FE) model of the human ear which was designed to simulate the response of the ear to the blast overpressure. In this study, biomechanical measurements were conducted on TM and ISJ specimens harvested from human cadaveric temporal bones (TB). The dynamic properties of the ISJ were measured using dynamic mechanical analyzer (DMA) at frequencies from 1 to 80 Hz at three temperatures of 5, 25 and 37 °C. The frequency-temperature superposition (FTS) principle was used to extrapolate the complex moduli of the ISJ specimens to 8 kHz. Then, the mechanical properties of ISJ under high-strain-rate deformation were measured by split Hopkinson tension bar. FE simulations on ISJ demonstrated that the behavior of the joint under harmonic and impulse loads was closely related to the structure and the mechanical properties of the joint components. For biomechanical measurement of the TM, the full-field surface motion of human TMs was measured by scanning laser Doppler vibrometry (SLDV) over a frequency range from 1 to 8 kHz under normal and post-blast conditions. An FE model of the human TM with multilayer microstructure and orthogonal fiber network was built and successfully characterized the features of the surface motion measured from the normal and damaged ears. The consistency between the experimental data and model simulation suggested that the blast-induced damage to the collagen fibers in the TM. To investigate the mechanism of the induction of the damage, a dual laser setup was established to capture the real-time motion of the TM in the period of time during which the blast waves were propagating through the ear. The motion of the TM umbo within 5 ms after the blast exposure arrived was measured and normalized by the blast pressure levels. The response of the ear was simulated by an FE model of human ear by applying the same input pressure at the entrance of the ear canal. The TM movement and pressure showed good consistency between the results the FE model prediction and the experimental data. The nonlinear behavior of the human middle ear under blast overpressure was observed. In this dissertation, the behavior of the human ISJ and TM in the normal and blast-damaged was characterized through a series of biomechanical measurements. The quantitative data can be used as input for FE models of the human ear to improve their accuracy on predicting the behavior of the ear under both normal and blast conditions. The methods used in this series of studies provide novel approaches for micron-level biomechanical measurement under dynamic or impulse loads

Flexibility within the middle ears of vertebrates

Introduction and aims: Tympanic middle ears have evolved multiple times independently among vertebrates, and share common features. We review flexibility within tympanic middle ears and consider its physiological and clinical implications. Comparative anatomy: The chain of conducting elements is flexible: even the ‘single ossicle’ ears of most non-mammalian tetrapods are functionally ‘double ossicle’ ears due to mobile articulations between the stapes and extrastapes; there may also be bending within individual elements. Simple models: Simple models suggest that flexibility will generally reduce the transmission of sound energy through the middle ear, although in certain theoretical situations flexibility within or between conducting elements might improve transmission. The most obvious role of middle-ear flexibility is to protect the inner ear from high-amplitude displacements. Clinical implications: Inter-ossicular joint dysfunction is associated with a number of pathologies in humans. We examine attempts to improve prosthesis design by incorporating flexible components

Comparison of Adaptive Optics Scanning Light Ophthalmoscopic Fluorescein Angiography and Offset Pinhole Imaging

Recent advances to the adaptive optics scanning light ophthalmoscope (AOSLO) have enabled finer in vivo assessment of the human retinal microvasculature. AOSLO confocal reflectance imaging has been coupled with oral fluorescein angiography (FA), enabling simultaneous acquisition of structural and perfusion images. AOSLO offset pinhole (OP) imaging combined with motion contrast post-processing techniques, are able to create a similar set of structural and perfusion images without the use of exogenous contrast agent. In this study, we evaluate the similarities and differences of the structural and perfusion images obtained by either method, in healthy control subjects and in patients with retinal vasculopathy including hypertensive retinopathy, diabetic retinopathy, and retinal vein occlusion. Our results show that AOSLO OP motion contrast provides perfusion maps comparable to those obtained with AOSLO FA, while AOSLO OP reflectance images provide additional information such as vessel wall fine structure not as readily visible in AOSLO confocal reflectance images. AOSLO OP offers a non-invasive alternative to AOSLO FA without the need for any exogenous contrast agent

Longitudinal imaging of microvascular remodelling in proliferative diabetic retinopathy using adaptive optics scanning light ophthalmoscopy

Purpose To characterise longitudinal changes in the retinal microvasculature of type 2 diabetes mellitus (T2DM) as exemplified in a patient with proliferative diabetic retinopathy (PDR) using an adaptive optics scanning light ophthalmoscope (AOSLO). Methods A 35-year-old T2DM patient with PDR treated with scatter pan-retinal photocoagulation at the inferior retina 1 day prior to initial AOSLO imaging along with a 24-year-old healthy control were imaged in this study. AOSLO vascular structural and perfusion maps were acquired at four visits over a 20-week period. Capillary diameter and microaneurysm area changes were measured on the AOSLO structural maps. Imaging repeatability was established using longitudinal imaging of microvasculature in the healthy control. Results Capillary occlusion and recanalisation, capillary dilatation, resolution of local retinal haemorrhage, capillary hairpin formation, capillary bend formation, microaneurysm formation, progression and regression were documented over time in a region 2° superior to the fovea in the PDR patient. An identical microvascular network with same capillary diameter was observed in the control subject over time. Conclusions High-resolution serial AOSLO imaging enables in vivo observation of vasculopathic changes seen in diabetes mellitus. The implications of this methodology are significant, providing the opportunity for studying the dynamics of the pathological process, as well as the possibility of identifying highly sensitive and non-invasive biomarkers of end organ damage and response to treatment

A mechatronic approach to supernormal auditory localisation

Remote audio perception is a fundamental requirement for telepresence and teleoperation in applications that range from work in hostile environments to security and entertainment. The following paper presents the use of a mechatronic system to test the efficacy of audio for telepresence. It describes work to determine whether the use of supernormal inter-aural distance is a valid means of approaching an enhanced method of hearing for telepresence. The particular audio variable investigated is the azimuth angle of error and the construction of a dedicated mechatronic test rig is reported and the results obtained. The paper concludes by observing that the combination of the mechatronic system and supernormal audition does enhance the ability to localise sound sources and that further work in this area is justified

Development of a dynamic virtual reality model of the inner ear sensory system as a learning and demonstrating tool

In order to keep track of the position and motion of our body in space, nature has given us a fascinating and very ingenious organ, the inner ear. Each inner ear includes five biological sensors - three angular and two linear accelerometers - which provide the body with the ability to sense angular and linear motion of the head with respect to inertial space. The aim of this paper is to present a dynamic virtual reality model of these sensors. This model, implemented in Matlab/Simulink, simulates the rotary chair testing which is one of the tests carried out during a diagnosis of the vestibular system. High-quality 3D-animations linked to the Simulink model are created using the export of CAD models into Virtual Reality Modeling Language (VRML) files. This virtual environment shows not only the test but also the state of each sensor (excited or inhibited) in real time. Virtual reality is used as a tool of integrated learning of the dynamic behavior of the inner ear using ergonomic paradigm of user interactivity (zoom, rotation, mouse interaction,…). It can be used as a learning and demonstrating tool either in the medicine field - to understand the behavior of the sensors during any kind of motion - or in the aeronautical field to relate the inner ear functioning to some sensory illusions

Efficient coding of spectrotemporal binaural sounds leads to emergence of the auditory space representation

To date a number of studies have shown that receptive field shapes of early sensory neurons can be reproduced by optimizing coding efficiency of natural stimulus ensembles. A still unresolved question is whether the efficient coding hypothesis explains formation of neurons which explicitly represent environmental features of different functional importance. This paper proposes that the spatial selectivity of higher auditory neurons emerges as a direct consequence of learning efficient codes for natural binaural sounds. Firstly, it is demonstrated that a linear efficient coding transform - Independent Component Analysis (ICA) trained on spectrograms of naturalistic simulated binaural sounds extracts spatial information present in the signal. A simple hierarchical ICA extension allowing for decoding of sound position is proposed. Furthermore, it is shown that units revealing spatial selectivity can be learned from a binaural recording of a natural auditory scene. In both cases a relatively small subpopulation of learned spectrogram features suffices to perform accurate sound localization. Representation of the auditory space is therefore learned in a purely unsupervised way by maximizing the coding efficiency and without any task-specific constraints. This results imply that efficient coding is a useful strategy for learning structures which allow for making behaviorally vital inferences about the environment.Comment: 22 pages, 9 figure

On the mechanism of response latencies in auditory nerve fibers

Despite the structural differences of the middle and inner ears, the latency pattern in auditory nerve fibers to an identical sound has been found similar across numerous species. Studies have shown the similarity in remarkable species with distinct cochleae or even without a basilar membrane. This stimulus-, neuron-, and species- independent similarity of latency cannot be simply explained by the concept of cochlear traveling waves that is generally accepted as the main cause of the neural latency pattern. An original concept of Fourier pattern is defined, intended to characterize a feature of temporal processing—specifically phase encoding—that is not readily apparent in more conventional analyses. The pattern is created by marking the first amplitude maximum for each sinusoid component of the stimulus, to encode phase information. The hypothesis is that the hearing organ serves as a running analyzer whose output reflects synchronization of auditory neural activity consistent with the Fourier pattern. A combined research of experimental, correlational and meta-analysis approaches is used to test the hypothesis. Manipulations included phase encoding and stimuli to test their effects on the predicted latency pattern. Animal studies in the literature using the same stimulus were then compared to determine the degree of relationship. The results show that each marking accounts for a large percentage of a corresponding peak latency in the peristimulus-time histogram. For each of the stimuli considered, the latency predicted by the Fourier pattern is highly correlated with the observed latency in the auditory nerve fiber of representative species. The results suggest that the hearing organ analyzes not only amplitude spectrum but also phase information in Fourier analysis, to distribute the specific spikes among auditory nerve fibers and within a single unit. This phase-encoding mechanism in Fourier analysis is proposed to be the common mechanism that, in the face of species differences in peripheral auditory hardware, accounts for the considerable similarities across species in their latency-by-frequency functions, in turn assuring optimal phase encoding across species. Also, the mechanism has the potential to improve phase encoding of cochlear implants