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BACKGROUND: Guidelines exist for counseling expectant families of infants at periviable gestational ages (22–25 weeks), but it is much more common for neonatologists to counsel families at gestational ages beyond the threshold of viability when several aspects of these guidelines do not apply. We aimed to develop an understanding of what information is shared with mothers at risk of preterm delivery beyond periviability and to evaluate communication skills of our participants. METHODS: We developed a checklist of elements to include in counseling based on a comprehensive literature review. The checklist was divided into an information sharing section and a connect score. The information sharing list was sub-divided into general information and specific complications. Neonatologists engaged in a simulated prenatal counseling session with a standardized patient. Videotaped encounters were then analyzed for checklist elements. RESULTS: Neonatologists all scored well in communication using our tool and two other validated communication tools - the SEGUE and the analytic global OSCE. There was no difference in scoring based on years of experience or level of training. Information sharing from neonatologists more often discussed general information over specific. Neonatologists also focused more on early outcomes over long-term outcomes. Only 12% of neonatologists quoted the correct survival rate for the case. CONCLUSIONS: Neonatologists generally communicate well but share less information specific to prematurity and the long-term sequelae of prematurity. Our tool may be used to test if other interventions improve information sharing or communication. [ABSTRACT FROM AUTHOR]

Competent elastic fibers endow central arteries with the compliance and resilience that are fundamental to their primary mechanical function in vertebrates. That is, by enabling elastic energy to be stored in the arterial wall during systole and then to be used to work on the blood during diastole, elastic fibers decrease ventricular workload and augment blood flow in pulsatile systems. Indeed, because elastic fibers are formed during development and stretched during somatic growth, their continual tendency to recoil contributes to the undulation of the stiffer collagen fibers, which facilitates further the overall compliance of the wall under physiologic pressures while allowing the collagen to limit over-distension during acute increases in blood pressure. In this paper, we use consistent methods of measurement and quantification to compare the biaxial material stiffness, structural stiffness, and energy storage capacity of murine common carotid arteries having graded degrees of elastic fiber integrity – normal, elastin-deficient, fibrillin-1 deficient, fibulin-5 null, and elastase-treated. The finding that the intrinsic material stiffness tends to be maintained nearly constant suggests that intramural cells seek to maintain a favorable micromechanical environment in which to function. Nevertheless, a loss of elastic energy storage capability due to the loss of elastic fiber integrity severely compromises the primary function of these central arteries. [ABSTRACT FROM AUTHOR]

Cell-populated collagen gels have provided significant insight into the cellular contractile mechanisms and cell-matrix interactions that are necessary for compacting and remodeling extant matrix. Nevertheless, little research has been devoted towards determining how cells entrench these deformations that contribute to establishing a preferred mechanical state. To this end, we examined the roles of two covalent matrix cross-linkers, i.e. tissue transglutaminase and lysyl oxidase, during global remodeling of the free-floating fibroblast-populated collagen lattice. Inhibition of tissue transglutaminase resulted in a reduced rate of compaction compared to controls during early remodeling (up to 2 days). In contrast, inhibition of lysyl oxidase did not alter the early compaction of these lattices, but it reduced the compaction after 2 days of culture. Acute inhibition of different contractile mechanisms suggested further that calcium-dependent contractility may have dominated during the initial remodeling of the collagen lattice before giving way to calcium-independent contractility at later times. In summary, these findings suggest that early remodeling of the free-floating collagen lattice is facilitated by calcium-dependent cell contraction while entrenchment is dominated by a tissue transglutaminase-mediated cross-linking of the extant matrix. As remodeling continues, however, lysyl oxidase increases its contribution, perhaps by consolidating de novo collagen fibrils into fibers to continue the remodeling while the cells transition to a more sustained, calcium-independent contractility. These results promise to influence future tissue engineering studies as well as computational simulations aimed at understanding matrix remodeling in complex in vivo situations. © 2015 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

SUMMARY We implemented a constrained mixture model of arterial growth and remodeling in a nonlinear finite element framework to facilitate numerical analyses of diverse cases of arterial adaptation and maladaptation, including disease progression, resulting in complex evolving geometries and compositions. This model enables hypothesis testing by predicting consequences of postulated characteristics of cell and matrix turnover, including evolving quantities and orientations of fibrillar constituents and nonhomogenous degradation of elastin or loss of smooth muscle function. The nonlinear finite element formulation is general within the context of arterial mechanics, but we restricted our present numerical verification to cylindrical geometries to allow comparisons with prior results for two special cases: uniform transmural changes in mass and differential growth and remodeling within a two-layered cylindrical model of the human aorta. The present finite element model recovers the results of these simplified semi-inverse analyses with good agreement. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Background: Four distinguishing histopathological characteristics of thoracic aortic aneurysms and dissections (TAADs) are the fragmentation or degradation of elastic fibers, loss of smooth muscle, pooling of glycosaminoglycans, and remodeling of fibrillar collagens. Of these, pooling of glycosaminoglycans appears to be unique to these lesions. Methods: This review acknowledges the importance of dysregulated transforming growth factor-β (TGF-β) in TAADs and offers a complementary hypothesis that increased TGF-β could contribute to the accumulation of glycosaminoglycans in the media of the proximal thoracic aorta. Regardless, observed pools of glycosaminoglycans could decrease tensile strength, cause stress concentrations, and increase intralamellar swelling pressure, all of which could initiate local delaminations that could subsequently propagate as dissections and result in a false lumen or rupture. Conclusions: There is a pressing need to investigate potential mechanical as well as biological consequences of accumulated glycosaminoglycans in TAADs and to elucidate responsible signaling pathways, with particular attention to synthetic cells of nonmesodermal lineage. Such research could provide insight into the mechanisms of dissection and the seemingly paradoxical role of the over-expression of a cytokine that is typically associated with fibrosis but is implicated in a degenerative disease of the aorta that can result in a catastrophic mechanical failure. Copyright © 2012 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Biological growth processes involve mass exchanges that increase, decrease, or replace material that constitutes cells, tissues, and organs. In most cases, such exchanges alter the structural makeup of the material and consequently affect associated mechanobiological responses to applied loads. Given that the type and extent of changes in structural integrity depend on the different constituents involved (e.g., particular cytoskeletal or extracellular matrix proteins), the continuum theory of mixtures is ideally suited to model the mechanics of growth and remodeling. The goal of this review is twofold: first, to highlight a few illustrative examples that show diverse applications of mixture theory to describe biological growth and/or remodeling; second, to identify some open problems in the fields of modeling soft-tissue growth and remodeling. [ABSTRACT FROM AUTHOR]

Elucidating regional material properties of arterial tissue is fundamental to predicting transmural stresses and understanding how tissue stiffness influences cellular responses and vice versa. Atomic force microscopy (AFM) was used to measure point-wise the axial compressive stiffness of healthy aortas and atherosclerotic plaques at micron level separation distances. Cross sections of plaques were obtained from a widely used animal model of atherosclerosis (ApoE-/- mice). Median point-wise values of material stiffness were 18.7 and 1.5 kPa for the unloaded healthy wall (n = 25 specimens) and plaque (n = 18), respectively. When the healthy wall was distended uniformly during AFM testing, two mechanically distinct populations emerged from comparisons of normal cumulative distributions, with median values of 9.8 and 76.7 kPa (n = 16). The higher values of stiffness may have been due to extended elastin, which was not present in the plaques. Rather, most plaques were identified via standard and immunofluorescent histology to be largely lipid laden, and they exhibited a nearly homogeneous linear elastic behavior over the small AFM indentations. Understanding the mechanics and mechanobiological factors involved in lesion development and remodeling could lead to better treatments for those lesions that are vulnerable to rupture. Copyright © 2011 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Quantifying mechanical properties of blood clots is fundamental to understanding many aspects of cardiovascular disease and its treatment. Nevertheless, there has been little attention to quantifying the evolving composition, structure and properties when a clot transforms from an initial fibrin-based mesh to a predominantly collagenous mass. Although more data are needed to formulate a complete mathematical model of the evolution of clot properties, we propose a general constrained mixture model based on diverse data available from in vitro tests on fibrinogenesis, the stiffness of fibrin gels, and fibrinolysis as well as histological and mechanical data from clots retrieved from patients at surgery or autopsy. In particular, albeit resulting from complex kinetics involving many clotting factors, we show that the rapid (minutes) in vitro production of fibrin from fibrinogen can be modeled well by an Avrami-type relation and similarly that the fast (tens of minutes) in vitro degradation of fibrin in response to different concentrations of plasmin can be captured via a single “master function” parameterized by appropriate half-times that can be inferred from laboratory or clinical data. Accounting simultaneously for the production and removal of fibrin as well as chemo-mechano-stimulated production of fibrillar collagens yields predictions of changing mass fractions and bulk mechanical properties that correspond well to experimentally available data. Constrained mixture models thus hold considerable promise for modeling the biomechanics of clot evolution and can guide the design and interpretation of needed experiments and stress analyses. [ABSTRACT FROM AUTHOR]

Describes cases of systemic infection with the deuteromycete fungi Cladosporium cladosporioides, Scopulariopsis brumptii and Ochroconis humicola involving the swim bladder of barramundi cod, Cromileptes altivelis from Australia. Characteristics of the barramundi cod.

Focuses on a study which described a theoretical framework to guide the performance and interpretation of biaxial tests on solid-fluid mixtures to identify forms of the response functions. Substances that can be modeled as mixtures of many constituents; Kinematics and basic governing equations for mixtures; Overview of the governing equations.

Heating therapies are increasingly used in cardiology, dermatology, gynecology, neurosurgery, oncology, ophthalmology, orthopedics, and urology, among other medical specialties. This widespread use of heating is driven primarily by the availability of new technology, not by a detailed understanding of the biothermomechanics. Without basic quantification of the underlying physical and chemical processes in terms of parameters that can be controlled clinically, identification of preferred interventions will continue to be based primarily on trial and error, thus necessitating large clinical studies and years of accumulative experience. Perusal of the literature reveals that much has been learned over the past century about the response of cells, proteins, and tissues to supra-physiologic temperatures; yet, the associated findings are reported in diverse journals and the underlying basic processes remain unidentified. In this review, we seek to contrast various findings on the kinetics of the thermal denaturation of collagen and to encourage investigators to consider the many open problems in part via a synthesis of results from the diverse literatures. [ABSTRACT FROM AUTHOR]

Presents information on a study which tested the hypothesis that aging results in increased vasoconstrictor responses of skeletal muscle resistance arterioles. Effects of the reductions in skeletal muscle blood flow; Characteristics of isolated blood vessels; Analysis of vasoconstrictor responses to pharmacological agents.

Intracranial saccular aneurysms remain an enigma; it is not known why they form, why they enlarge, or why only some of them rupture. Nonetheless, there is general agreement that mechanics plays an essential role in each aspect of the natural history of these potentially deadly lesions. In this paper, we review recent findings that discount limit point instabilities under quasi-static increases in pressure and resonance under dynamic loading as possible mechanisms of enlargement of saccular aneurysms. Indeed, recent histopathological data suggest that aneurysms enlarge due to a stress-mediated process of growth and remodeling of collagen, the primary load-bearing constituent within the wall. We submit that advanced theoretical, experimental, and numerical studies of this process are essential to further progress in treating this class of pathologies. The purpose of this review is to provide background and direction that encourages elasticians to contribute to this important area of research. [ABSTRACT FROM AUTHOR]

Well accepted descriptors of the thermoelastic behavior of elastomers undergoing finite strain remain elusive largely due to the continuing lack of appropriate multiaxial data. In this paper we present a new theoretical framework for inferring thermoelastic constitutive relations directly from biaxial data. In particular, we consider an experimentally natural decomposition of the motion into two parts – one due to traction-free uniform heating and one due to isothermal mechanical loading – and impose a mechanical incompressibility constraint on each motion. It is shown that, regardless of the order of the motions, one obtains a thermoelastic generalization of the classical result of Rivlin and Saunders for identifying response functions from (isothermal) biaxial data. [ABSTRACT FROM AUTHOR]

Presents information on a method used to study steady-state diffusion of a fluid within a finitely deformed nonlinearly elastic solid. Description of the boundary value problem; Details on the numerical solutions to the problems; Information on the theory of mixtures.