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Tissue Properties (tissue + property)
Selected AbstractsMechanisms for Discordant AlternansJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 2 2001MARI A. WATANABE M.D., Ph.D. Discordant Alternans Mechanism.Introduction: Discordant alternans has the potential to produce larger alternans of the ECG T wave than concordant alternans, but its mechanism is unknown. Methods and Results: We demonstrate by one- and two-dimensional simulation of action potential propagation models that discordant alternans can form spontaneously in spatially homogeneous tissue through one of two mechanisms, due to the interaction of conduction velocity and action potential duration restitution at high pacing frequencies or through the dispersion of diastolic interval produced by ectopic foci. In discordant alternans due to the first mechanism, the boundaries marking regions of alternans with opposite phase arise far from the stimulus site, move toward the stimulus site, and stabilize. Dynamic splitting of action potential duration restitution curves due to electrotonic coupling plays a crucial role in this stability. Larger tissues and faster pacing rates are conducive to multiple boundaries, and inhomogeneities of tissue properties facilitate or inhibit formation of boundaries. Conclusion: Spatial inhomogeneities of electrical restitution properties are not required to produce discordant alternans. [source] The compressive creep properties of normal and degenerated murine intervertebral discsJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 1 2004Erika I. Palmer Abstract Identifying mechanisms by which degeneration alters intervertebral disc material properties and biomechanical behavior is important for clarifying back pain risk factors as well as for evaluating the efficacy of novel interventions. Our goal was to quantify and characterize degeneration-dependent changes in the disc's response to compression using a previously established murine model of disc degeneration. We performed compressive creep tests on normal and degenerated murine intervertebral discs and parameterized the biomechanical response using a previously established fluid-transport model. Using a series of biochemical and histological assays, we sought to determine how biomechanical alterations were attributable to degeneration-related changes in tissue morphology. We observed that with moderate degeneration, discs lost height (mean ± std. dev. of 0.44 ± 0.01 vs. 0.36 ± 0.01 mm, p < 0.0001), increased in proteoglycan content (31 ± 4 vs. 43 ± 2 ,g/ml of extract, p < 0.0002), became less stiff (2.17 ± 0.66 vs. 1.56 ± 0.44 MPa, p < 0.053), and crept more. Model results suggested that the increased creep response was mainly due to a diminished strain-dependent nuclear swelling pressure. We also noted that the model-derived tissue properties varied with the applied load magnitude for both normal and degenerated discs. Overall, our data demonstrate that architectural remodeling stimulated by excessive loading diminishes the disc's ability to resist compression. These results are similar to degeneration-dependent changes reported for human discs. © 2003 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source] Laser applications and system considerations in ocular imagingLASER & PHOTONICS REVIEWS, Issue 5 2008A.E. Elsner Abstract We review laser applications for primarily in-vivo ocular imaging techniques, describing their constraints based on biological tissue properties, safety, and the performance of the imaging system. We discuss the need for cost-effective sources with practical wavelength-tuning capabilities for spectral studies. Techniques to probe the pathological changes of layers beneath the highly scattering retina and diagnose the onset of various eye diseases are described. The recent development of several optical-coherence-tomography-based systems for functional ocular imaging is reviewed, as well as linear and nonlinear ocular-imaging techniques performed with ultrafast lasers, emphasizing recent source developments and methods to enhance imaging contrast. [source] Displacement and recovery of the vesical neck position during pregnancy and after childbirth,NEUROUROLOGY AND URODYNAMICS, Issue 3 2007Jacobus Wijma Abstract Aims (i) To describe the displacement and recovery of the vesical neck position during pregnancy and after childbirth and (ii) to discriminate between compliance of the vesical neck supporting structures with and without pelvic floor contraction. Methods We focussed on the biomechanical properties of the vesical neck supporting structures during pregnancy and after childbirth by calculating the compliance and the hysteresis as a result from of abdominal pressure measurements and simultaneous perineal ultrasound. Results This study shows that compliance of the supporting structures remains relatively constant during pregnancy and returns to normal values 6 months after childbirth. Hysteresis, however, showed an increase after childbirth, persisting at least until 6 months post partum. Conclusions Vaginal delivery may stretch and or load beyond the physiological properties of the pelvic floor tissue and in this way may lead to irreversible changes in tissue properties which play an important role in the urethral support continence mechanism. Neurourol. Urodynam. 26:372,376, 2007. © 2007 Wiley-Liss, Inc. [source] | ||||||||||