1,720,981 research outputs found
Modeling blood flow in viscoelastic vessels: the 1D augmented fluid–structure interaction system
No full textNowadays mathematical models and numerical simulations are widely used in the field of hemodynamics, representing a valuable resource to better understand physiological and pathological processes in different medical sectors. The theory behind blood flow modeling is closely related to the study of incompressible flow through compliant thin-walled tubes, starting from the incompressible Navier–Stokes equations. Furthermore, the mechanical interaction between blood flow and vessels wall must be properly described by the model. Recent works showed the benefits of characterizing the rheology of the vessel wall through a viscoelastic law. Taking into account the viscous contribution of the wall material and not simply the elastic one leads to a more realistic representation of the vessel behavior, which manifests not only an instantaneous elastic strain but also a viscous damping effect on pulse pressure waves, coupled to energy losses. In this context, the aim of this work is to propose an easily extensible one-dimensional mathematical model able to accurately capture fluid–structure interactions. The originality of the model lies in the introduction of a viscoelastic tube law in PDE form, valid for both arterial and venous networks, leading to an augmented fluid–structure interaction system. In contrast to well established mathematical models, the proposed one is natively hyperbolic. The model is solved with an efficient and robust second-order numerical scheme; the time integration is based on an Implicit–Explicit Runge–Kutta scheme conceived for applications to hyperbolic systems with stiff relaxation terms. The validation of the proposed model is performed on several different test cases. Results obtained in Riemann problems, adopting a simple elastic tube law for the characterization of the vessel wall, are compared with available exact solutions. To validate the contribution given by the viscoelastic term, the Method of Manufactured Solutions has been applied. Specific tests have been designed to verify the well-balancing with respect to fluid-at-rest condition and the accuracy-preserving property of the scheme. Finally, a specific test case with an inlet pulse pressure wave has been designed to assess the effects of viscoelasticity with respect to a simple elastic behavior of the vessel wall. The complete code, written in MATLAB (MathWorks Inc.) language, with the implemented test cases, is made available in Mendeley Data repository
Diuretics and dopamine for the prevention and treatment of acute renal failure: a critical reappraisal.
No full textThe efficacy of diuretics and dopamine in preventing and treating acute renal failure (ARF) is still debated, although these drugs are widely used in clinical practice. The present review addresses this debate providing an update on available data. There are very few well controlled and sufficiently large trials testing these agents in different ARF clinical settings, with either a preventive or a curative goal. Unfortunately, most findings rule out any favourable effects of diuretics, mannitol, atrial natriuretic peptides, and dopamine. In fact, at least in some clinical conditions, they can even worsen the risk of ARF or aggravate its course
Diuretics and dopamine for the prevention and treatment of acute renal failure: a critical reappraisal.
No full textThe renal handling of uric acid in the elderly
No full textIn 25 elderly subjects the renal handling of uric acid was investigated to clarify the discrepancy between the substantially normal and stable serum concentration of uric acid and the reduction of glomerular filtration rate in the elderly. The urate clearance and fractional clearance were increased in respect to a young control group. There was no relationship to different values of glomerular filtration rate. These data suggest an abnormal renal handling of urate at the tubular level, and explain the normal blood uric acid in the elderly. Our observations, confirm the existence of tubular dysfunction in the ageing kidney
Systematic Experimental Tests for the IMO Weather Criterion Requirements and Further Development Towards a Probabilistic Intact Stability Approach
No full textThe Possible Evolution of Weather Criterion for Ships with High Values of KG/T and B/T and Its Impact on Design
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