Experimental and Model Study of a Swirling Fluid Flow in a Converging Channel As a Simulation of Blood Flow in the Heart and Aorta.

Study of swirling flows in channels corresponding to the static approximation of flow channels of the heart and major vessels with a longitudinal-radial profile zR2 = const and a concave streamlined surface at the beginning of the longitudinal coordinate has been carried out. A comparative analysis of the flow structure in channel configurations zRN = const, where N = -1, 1, 2, 3, in the absence and presence of a concave surface was carried out. The numerical modeling was compared with the results of hydrodynamic experiments on the flow characteristics and the shape of the flow lines. The numerical model was used to determine the velocity structure, viscous friction losses, and shear stresses. Numerical modeling of steady-state flows for channels without a concave surface showed that in the channel zR2 = const there is a stable vortex flow structure with the lowest viscous friction losses. The presence of a concave surface of sufficient size significantly reduces viscous friction losses and shear stresses in both the steady state and pulsed modes.

[SCREENING ASSESSMENT OF MATERIALS THROMBOGENICITY BY THE NUMBER OF PLATELETS ADHERED FROM THE FLOWING NATIVE BLOOD].

The materials used in the construction of implants contacting with blood should be resistant to thrombus formation. One of the stages of a thrombogenicity assessment of materials is to determine the number of platelets adhered to its surface during the exposure to flowing blood under ex viAvo conditions. The aim of this study was to develop a modified test for screening assessment of materials for their thrombogenicity in contact with native blood. For the purpose of the study, flow chambers of were developed, allowing to mountain simultaneously 16 material samples. The chamber was connected to the circulatory system of the experimental animal through arterial and venous ports in such a way that blood, passing through the chamber, returned to the animal. The exposure time was 1 min. After perfusion the samples were rinsed and stained. The number of platelets adhered per unit area was calculated automatically that allowed significant error diminution. A total of 9 experiments were carried out on pigs under ex vivo conditions. The method was validated using standard samples of pyrolytic carbon, VT-6 titanium, glass, and polytetrafluorethylene as reference materials. New materials for synthetic vascular prostheses have been investigated. The developed technique makes it possible to study the thrombogenicity of polymeric materials with sufficient reliability.

The Effect of Mechanical Compatibility and of Thrombogenicity on the Ingrowth of a New Synthetic Vascular Prosthesis (Experimental Study).

Common disadvantages of modern synthetic vascular prostheses are thrombogenicity and lack of biomechanical compatibility with the prothesized vessel. To elucidate the role of these factors in the prosthesis integration, prostheses specimens were made by the electrospinning from the known materials: polycaprolactone, polyurethane and a mixture of fluorine-containing synthetic rubber FKM-26 with fluoroplastic F-26. The germination of the prostheses was compared with standard e-PTFE prosthesis in the pigs infrarenal aorta. The elastic properties of prostheses were studied by elastometry under the physiological range of loads. The thrombogenicity of the materials was determined by the number of platelets adhered to material surface exposed to native blood. The patency of the prostheses was checked by aortography. The germination of prostheses was assessed in the histological examination. It was shown that, with this set of materials, biomechanical compatibility turned out to be a more important factor of integration than the material thrombogenicity.

The Hydrodynamics of a Swirling Blood Flow in the Left Heart and Aorta.

This paper proposes a new approach to the quantitative analysis of the hydrodynamic structure of a blood flow in the flow channel running from the left atrium to the end of the aorta. This approach is based on the concept of the structural organization of tornado-like swirling jets in channels with a given geometric configuration. Considering the large amount of experimental data in our possession, it was shown that along the entire length of the flow channel, conditions exist for the generation and maintenance of a swirling structure of the jet throughout the entire cardiac cycle. This study has given rise to a new direction in research in fundamental physiology and medicine, which is of great practical importance for diagnosing and treating circulatory disorders accompanied by changes in the geometric configuration and biomechanical characteristics of the heart and great vessels.

Analysis of Dynamic Geometric Configuration of the Aortic Channel from the Perspective of Tornado-Like Flow Organization of Blood Flow.

Analysis of the data of morphometry of aortic casts, aortography at different pressures, and multispiral computer tomography of the aorta with contrast and normal pulse pressure showed that geometric configuration of the flow channel of the aorta during the whole cardiac cycle corresponded to the conditions of self-organization of tornado-like quasipotential flow described by exact solutions of the Navier-Stokes equation and continuity of viscous fluid typical for this type of fluid flows. Increasing pressure in the aorta leads to a decrease in the degree of approximation of the channel geometry to the ratio of exact solution and increases the risk of distortions in the structure of the flow. A mechanism of evolution of tornado-like flow in the aorta was proposed.

[COMPARATIVE EVALUATION OF THE DYNAMIC BIOMECHANICAL COMPATIBILITY OF SYNTHETIC VASCULAR PROSTHESES IN VITRO, EX VIVO AND IN VIVO].

Previously, the pattern of changes in the radial elasticity of the aortic wall in the longitudinal direction has been shown, which poses new challenges in the selection of the biomechanical properties of synthetic prostheses for replacing arterial vessels. The aim of the work was to develop a system of methods for assessing the biomechanical properties of vascular implants, allowing supplementing the known methods of testing on thromboresistance and healing. Samples of blood vessels prostheses were prepared using electrospinning technology with the polymer composition and the conditions of prosthesis formation so that their elastic properties in the physiological pressure range were as close as possible to the properties of native blood vessels. The following test methods were used: in vitro - elastometry on a universal testing machine under static and cyclic loading; ex vivo - tests on a hemodynamic test bench connected to the circulation of a pig; in vivo - implantation of vascular prostheses in a chronic experiment on pigs. The testing has shown a close correspondence of the elastic characteristics of the prostheses under static loading and tests on the hemodynamic bench was revealed. Under cyclic loading, a significant excess of the compliance of the prostheses on the hemodynamic bench was detected. In vivo tests in chronic experiments confirmed the results of testing on a hemodynamic bench. The results of the tests have shown that the synthetic prostheses manufactured by electrospinning technology, have a radial compliance of up to 15%. The proposed ex vivo test method makes it possible to obtain data that are necessary to optimize the requirements for the parameters of the manufactured prostheses matrices.

Experimental Evaluation of Biodegradable Film Compositions Based on Gelatin with Colchicine.

Biodegradable film compositions based on natural biopolymer gelatin with immobilized colchicine were prepared and their efficiency in prevention of the adhesion process in the pericardium was evaluated on rabbit model of postoperative pericarditis. The use of gelatin-based biodegradable film compositions significantly reduced the intensity of adhesion formation in the pericardial cavity, while immobilization of anti-inflammatory drug colchicine amplified their anti-adhesion activity.

[Quantitative Evaluation of Intracardiac Blood Flow by Left Ventricle Dynamic Anatovy Based On Exact Solutions of Non-Stationary Navier-Stocks Equations for Selforganized tornado-Like Flows of Viscous Incompresssible Fluid].

New approach to intracardiac blood flow condition analysis based on geometric parameters of left ventricle flow channel has been suggested. Parameters, that used in this method, follow from exact solutions of nonstationary Navier-Stocks equations for selforganized tornado-like flows of viscous incompressible fluid. The main advantage of this method is considering dynamic anatomy of intracardiac cavity and trabeculae relief of left ventricle streamlined surface, both registered in a common mri-process, as flow condition indicator. Calculated quantity options that characterizes blood flow condition can be use as diagnostic criterias for estimation of violation in blood circulation function which entails heart ejection reduction. Developed approach allows to clarify heart jet organization mechanism and estimate the share of the tornado-like flow self-organization in heart ejection structure.

[Progress in cardiovascular surgery: new analytical, experimental, and technological approaches].

Blood flow in heart and main vessels is a self-organizing eddy flow described by Kiknadze-Krasnov's non-stationary hydrodynamic equations. Their exact solutions are applicable to simulation of blood circulation in normal and pathological conditions, quantitative evaluation of efficiency of surgical treatment of cardiovascular diseases, and designing implantable devices for cardiovascular surgery to support physiological blood flow structure. An essentially new all-flow three-leaflet CorBit artificial heart valve from pyrolyitic carbon has been proposed to maintain physiological blood flow with minimal regurgitation and transvalvular pressure gradient. The CorBit valve allows to normalize hemodynamic parameters soon after implantation. Also, manufacture is underway of a wide range of original stented and stentless bioprostheses of heart valves and valve-containing BioLab conduits from allogenic and xenogenic biological tissues. BioLab bioprostheses are currently widely used to treat complicated congenital and acquired forms of cardiopathology.

In vitro and in situ intercellular adhesion molecule-1 (ICAM-1) expression by endothelial cells lining a polyester fabric.

In order to improve long-term patency of vascular grafts, the promising concept of endothelial cell seeding is actually under investigation. Our laboratory tested a polyester coated with albumin and chitosan which permits a rapid colonization by human umbilical vein endothelial cells (HUVEC) and it seems relevant to test in vitro the expression of adhesive molecules expressed by cells with regard to the inflammatory process. We studied intercellular adhesion molecule-1 (ICAM-1) expression and focused our work on the determination of ICAM-1 sites expressed per adherent cell lining the biomaterial, thus in situ, in comparison to control HUVEC on plastic wells: the results obtained by binding experiments were correlated to flow cytometry analyses and showed that the polyester does not induce a proinflammatory state and that HUVEC covering the structure are able to respond to a stimulus.

An in vivo comparative study of the e-polytetrafluoroethylene vascular prostheses: Vitaflon and Gore-Tex.

A comparative study was performed in order to validate new Russian e-PTFE vascular prostheses Vitaflon (St. Petersburg, Russia). The Gore-Tex prostheses were chosen as a referential model. The prostheses were implanted in the venous and arterial positions in 13 dog experiments. After the implantation time was over a comprehensive histological and histochemical examination of excized specimens was performed. It was demonstrated that there is no difference in healing and functional properties between the two studied prostheses.

Endothelial cells lining polyester fabric express pro-coagulant phenotype in vitro.

The paper deals with the in vitro assessment of endothelial cell (EC) phenotype covering an albumin- and chitosan-coated polyester fabric and shows that resting ECs express a pro-coagulant phenotype by releasing a high von Willebrand factor level and expressing low thrombomodulin surface activity, despite maintaining an adequate response to stimulating agents.

Up-regulation of thrombomodulin is inducible on an endothelialized polyester.

The concept of endothelial cell seeding of vascular prostheses is designed as a method for improving long-term patency substitutes because endothelium is considered as the haemocompatible surface of reference. The assessment of the functionality of cells lining a biomaterial is thus of crucial importance. We have reported encouraging results concerning the ability of a polyester coated with albumin and chitosan (M 11) to be lined by a confluent monolayer of cultured human endothelial cells (EC). The aim of the present work was to study the expression of thrombomodulin (membrane glycoprotein responsible for anticoagulant activity) in EC lying on M.11 by anticoagulant activity and mRNA level with and without stimulation. Results obtained in basal conditions showed that EC on M.11 have a comparable expression of TM mRNA when compared to control (EC on tissue culture plates) despite a lower TM surface activity for EC on the biomaterial. In terms of ratio (stimulated cells to unstimulated ones) the response in activity for EC on M.11 is comparable to that of the control. These results indicate that cells lying on M.11 are able to respond to physiological-like stimuli, despite a tendency for these cells to express a procoagulant phenotype when compared with control EC.

[Evaluation of the function of the left heart ventricle during the modeling of right ventricular hyperfunction using a pulsatile pump]. / Otsenka funktsii levogo zheludochka serdtsa pri modelirovanii pravozheludochkovoi giperfunktsii s pomoshch'iu pul'siruiushchego nasosa.

Left ventricular function was studied in 11 acute experiments on dogs during right ventricular hyperfunction modelling using an artificial heart ventricle (AHV). The right ventricle was excluded from circulation and replaced by AHV. First the baseline condition with regard to the cardiac index was recovered. The right ventricle was considered to be completely functionally replaced when no hemodynamic changes were observed. When the AHV output increased by 26% there were no considerable changes in hemodynamics and the functional condition of the left ventricle remained adequate. If the output was 56% higher certain hemodynamic changes and a tendency towards deterioration of the left ventricular function have been observed. The final stage of the experiments was characterized by twice as high ANV output, as compared to the initial one, which caused considerable hemodynamic changes and greater left ventricular weakness.