Clinical Medicine

Doct. of med. sci., Prof. A.L. Isakadze, Prof. G.G. Eliava, Prof. T.G. Tsintsadze,

Prof. T.Sh. Buachidze, Asoc. prof. L.S. Topuria, Cand. of biol. sci. L.G. Berulava

Visco-elastic properties of blood vessels and role of their change in the development of pathological processes

Tbilisi State Medical University

Georgian Technical University, Department of Pharmacy

Study of strength and deformation properties of blood vessel walls, establishment of regularities of their change, biochemical modeling taking into account muscular activity of walls, as well as computer technologies of study are of great importance in biology and medicine (Dol А.V., 2013; Gulyaev Yu.P., 2009; Bеgun I., Krivokhizhina О.V., Panteleeva N.А., 2009; Belikov N.V., Маrkоvа N.V., 2011 etc.).

Study of visco-elastic properties of blood vessels is also very important for manufacturing of tissular prosthesis of blood vessels, which are characterized by biological activity. However, at present there are virtually no materials, implantation of which in the organism doesn’t induce more or less expressed inflammatory response from surrounding tissues. From this viewpoint the growth of biocompatibility of polymer materials using nanomaterials and nanotechnologies, namely the use of nanostructured fibres with high biological activity appears to be prospective. Manufacturing of such prostheses of blood vessels, in which the advantages of biologically active and biologically inert synthesized fibres are combined, is also prospective (Kasyanov V.A., Lukyanchikov A.A., Kantsevich V.A., 2013; Charkowsky A.V. et al, 1999, 2002 etc.).

Tissued PGA scaffold, both separately and in combination with other biodegradable polymers is used for regeneration of blood vessels (N. Kebadze, R. Katsarava, 2013; Shinoka T., Shum-Tim D., Ma P.X. et al. 1998; Niklason L.E., Gao J., Abbott W.M. et al. 1999). Despite of the fact that biodegradable polymers (fiber biodegradable polyglycol (PGA, A), PLA, other semi-crystalline polymers) are used not only in regeneration of blood vessels, but also of other biological tissues, (Freed L.F., Langer R., Martin I., Pellis N.R., 1997; Cao Y., Vacanti J.P., Ma X., et al., 1994 etc.), they have low mechanical strength (properties similar to wall-constituent structural elements’ features are not repeated), rapid degradation, and cross-section of pores and entire fibres are not optimally controlled. That’s why in this case for recovery of conductivity of blood vessels is preferable to use (if it is possible) other areas of own or donor’s blood vascular system. New class biodegradable polymers _ AABBP (Amin Acid Based Biodegradable Polymers), which are characterized by nontoxicity and involvement in metabolic processes taking place in the organism, is more than prospective (Lee S.H., Szindi I., Carpenter K., Katsarava R. et al., 2002; Tsitlanadze G., Machaidze M., Kviria T. et al., 2004; Kebadze N., Katsarava R., 2013).

Elastic properties of artery walls are determined by fibres of elastin, collagen and smooth muscles. Up to 200-300% deformations are acceptable for elastin, its Young modulus is variable and is within the limits of 1·10⁵-6·10⁵ Pa; pure collagen is less strained, limit deformations reach 10%, and modulus of elasticity is within the limits of 1·10⁷-10·10⁸ Pa.

Tone activity of smooth muscles, their length and lumen, i.e. mechanical properties in general are changed under the influence of neural and humoral factors. Proceeding from this fact, the Young’s modulus of entirely relaxed smooth muscles is equal to 1·10⁴ Pa, while in physiologically active conditions it increases almost twice.

Tone activity of blood vessels have a certain impact on blood circulation. Using one-dimension model a volumetric blood flow at the outlet of blood vessels was determined in the MathCad program with regard to muscle activity of blood vessel walls or without it. It turned out that volumetric blood flow at the outlet of blood vessels, when muscle coefficient is 0,001, at the expense of reactive movement of walls, increases by 5% average (Dol A.V., 2013; Gulyaev Yu.P., Dol A.V., 2009 etc.).

Ratio of three basic components in artery walls depends on location of artery. Ratio of elastin and collagen in chest’s aorta is equal to 1,5 approximately. This ratio decreases in blood vessels distant from the heart, while ratio of elastin to collagen is 0,5 approximately in femoral artery.

The more distant is artery from heart periphery the more is the share of smooth muscle in dry mass of the wall.

Share of smooth muscle in chest aorta is 25%, while in smallest arteries and arterioles it reaches 60%. Venous structure is basically similar to artery’s structure, but their walls are more thin and contains less elastin (Waldman V.A., 1947; Ivanov Yu.A., 2009; Savitsky N.N., 1963 etc.).

Changes in biomechanical properties of venous vessels often cause varix dilatation and other diseases (Pokrovsky A.V., 1979; Kostenko I.G., 1979; Sinitsyn A.A., 1975; Borisova L.F., 1984 etc.). Injuries of magistral veins of lower limbs are especially wide-spread (Bortyuk N.Ya., Golyak Yu.V., 2013; Baeshko A.A., 2007; Grinfeld E.S., 2010). According to L. Borisova’s researches (1984) two types of dynamics of filling of limb’s venous vessels was determined after artificial occlusion. In case of the first type a filling rate decreases down to the time of reaching a plateau, while for second type the rate decreases at first, and afterward remains virtually unchangeable before reaching a plateau. These two types aren’t changed during transmural pressure change. First type of dynamics is distinctive for healthy persons of both sexes, while the second one – for patients suffered with low limb vein diseases. Family venous vessel diseases are mentioned in 70% of cases related with healthy persons having second type dynamics. Author explains these changes by various ratio of collagen and elastin fibres. After removal of occlusion a response of venous vessels in the first phase of emptying is basically determined by collagen fibres, while in the second phase – by collagen and elastin fibres. Mathematical modeling showed that in case of the I type of dynamics a modulus of effective tangent elasticity decreases 5,94±1,6 times, while for second type it reduces only 2,44±0,45 times, that author explains by the reason that ratio of collagen and elastin is changed. Collagen prevails in patients with second type dynamics and this fact is associated with increase in vein wall hardness.

Significant difference in values of mechanical parameters of arteries and veins is explained by different methodological approaches and impact of biological and abiologial factors. Biological factors include: age of human or animal, gender, disease, cause of death, activity of physiological functions of tissues; blood vessels localization etc. Abiological factors are as follows: sample humidity, conservation type, sample localization, test temperature, loading speed, ways of deformation measurement, test type. Besides abovementioned, it is necessary to take into account the deformation ability of blood vessel walls and anisotropy of material properties (Purinya B.А., Kasyanov V.А., 1980; Ivanov D.V., 2007).

Both in living organism and in the corpse all blood vessels are in certain stress condition. Strain of human corpse femoral artery’s wall is equal longitudinally to 2,0-2,5 gf/mm², while strain of big subcutaneous vein is 1,8-0,4 gf/mm². Temperature growth in the range from 10°C to 45°C causes compression of femoral artery and simultaneous 40-45% increase of strain. Temperature growth in venous segment in contradistinction from arteries causes strain relaxation. Linear dependence between artery segment’s strain and temperature is established in humans aged up to fifteen years. In elderly age (60 years) this dependence takes apparent nonlinear form. Above mentioned changes can be explained by different ratio of elastin, collagen and muscle elements in arteries and veins depending on age (Alexandr R., 1980; Wolkenstein М.V., 1988; Glazer R., 1988; Carot К., Pedley Т., Schroter R., Sid U., 1981; Begun P.М., Shukeilo Yu.А., 2000 etc.).

In our opinion, age-related natural changes of elastin, collagen and muscle elements ratio, along with other factors (low limbs edema, lymphostasis, age more than 71 years old, chronic heart failure, surgical operation in anamnesis) may become a risk-factors of deep venous thrombosis (Bovtyuk N.Ya., Golyak Yu.V., 2013; Grinfeld E.S., 2010 etc.).

Thus, visco elastic properties of blood vessels, along with neural and humoral factors significantly determine the operation of cardio-vascular system.

In the process of study of arterial and venous vessels it is important to take biological and abiological factors into account. For blood vessels’ regeneration will be prospective the use of such biopolymers on the basis of nanomaterials and nanotechnology, which have not inflammation-inducing effects, are characterized by nontoxicity and involvement in metabolic processes, so such combination with other polymers is necessary, which comes close to mechanical strength determined by three basic components (elastin, collagen and muscle elements) of artery wall; special attention should be paid to low limbs’ blood vessels, where content of elastin drastically decreases for sure that may become a risk factor of vein wall stiffening and development of venous thromboembolism. That’s why subclinical study of arteries and veins and especially blood vessels distant from heart, as well as study of parameters of biomechanical properties and in case of necessity timely carrying out of anti-inflammatory and thrombolytic therapy is of great importance.