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Kalandarov Dilmurod Madaminovich, candidate of medical sciences, associate professor, Head of the Department of General Practitioner - 2 Mirzakarimova Dildora Bakhodirovna, candidate of medical sciences, associate professor, Head of the Department of Infectious Diseases Primkulova Gulbahor Nazirjanovna, assistant of the Department of Propedeutics of Internal Diseases Khudoyarova Nazokatxon Kakharovna, senior teacher of the Department of General Practitioner - 2
Zhuraboev Bakhtierzhon, candidate of medical sciences, General Practitioner - 2 Andijan State Medical Institute Uzbekistan. City of Andijan
E-mail: [email protected]
THE STATE OF MICROCIRCULATION IN HYPERTENSION
Abstract: This review discusses the development of hypertension at the level of pathophysiology. We concider violations of the capillary blood circulation, which have am important and basic role in the occurrence ofhypertension. Keywords: hypertension, microcirculation disorder, capillary circulation.
It is impossible to objectively assess the state of hemodynamics as a whole without a thorough study of microcir-culatory changes, based only on the characteristics of large and medium caliber vessels. In recent years, the problem of microcirculation, in particular changes in the vessels of the microvasculature against the background of hypertension, has attracted the attention of many researchers and clinicians. The value of the capillary channel for the circulatory system is difficult to overestimate, because it is on the capillary level that the main metabolic processes occur, the effectiveness of which ensures the maintenance of homeostasis of all organs and body systems [5, 12]. Another major task of the microcirculatory bed (MCR) is the prevention of excessive hydrostatic pressure drops, which adversely affect capillary exchange. Resistive vessels - arterioles and venules in the pre- and postcapillary regions of the vascular bed, respectively - provide a regional distribution of cardiac output [12; 13]. It is known that in most forms of hypertension, the total peripheral vascular resistance (PVR) is increased [5]. This is especially characteristic of the late stages (steady state), when the cardiac output is usually not changed, and the increase in blood pressure is determined mainly by increased vascular resistance. The presence of a direct relationship between vascular resistance and the level of blood pressure, as was shown in the works of V. Folkow, can be explained by the Laplace law (pressure is equal to the ratio of voltage to radius) [15; 13]. Research results G. W. Schmidt-Schonbeinetal. clearly demonstrated that a decrease in the diameter
of arteriols by 13% leads to an increase in blood pressure of 48-50 mm Hg. st. under conditions of constant blood current [17]. The key factors contributing to the formation of increased resistance in GB are the number and diameter of actively functioning microvessels, the viscosity of the blood flowing through them, as well as the overall length and geometry of the microvascular network [19]. In the pathological process involved all these links. Conventionally, there are three variants of morphofunctional changes in the vessels of the microvasculature in GB [8]: - violation of the regulation of vascular tone with a relative predominance of vasoconstrictor phenomena; - violation of the structure of resistive vessels, an increase in the ratio of wall thickness to the diameter of the vessel lumen, stagnation in venules; - decrease in the density of the microvasculature (rarefaction). There are several types of remodeling of resistive vessels on the background of GB [18]. Eutrophic remodeling is characterized by a decrease in the external diameter and lumen of the court, an increase in the ratio "media thickness / light of the court". At the same time, the severity of the medial layer remains almost unchanged. This option is observed with a "soft" and short course of GB. The rigidity of the vessel wall remains at the same level. In hypertrophic remodeling of small-caliber arteries and arteriol, an increase in the "media / lightness of the court" ratio and the thickening of the medial layer of the vascular wall occur. May occur with symptomatic hypertension, primarily in the renovascular form. In hypotrophic remodeling, a decrease in the thickness
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of the muscular layer and an increase in the glossary flux are observed. Such changes are possible against the background of active hypotensive therapy, under the influence of which the hypertrophy of the medial membrane of the arterial wall occurs. Equally important is the hereditary factor [6]. Rar-efication is a decrease in the density of the microvascular network or a decrease in the number of functioning mi-crovessels [8]. This phenomenon is observed in different variants of hypertension. 30 The processes of dilution of microvessels proceed in two stages. The first one is essentially functional and is characterized by the prevailing influence of the vasoconstrictor neurohumoral stimuli on the active capillary network. It is important to note that at this stage the number of actively functioning capillaries can increase and even return to normal under the influence of factors contributing to vasodilation [12]. A distinctive feature of the second stage of the racification of the MCR is the morphological reduction of microvessels, i.e., the changes become organic. The number of actively functioning capillaries does not return to normal, and even the maximum dilation of the existing microvessels is not able to maintain tissue perfusion at the same level. H. A. Struijker-Boudieretal. suggested a hypothesis according to which the dilution of the MCR is a consequence of an imbalance between the factors of angiogenesis and antiagiogenesis with the latter predominating [18]. Thoma put forward three postulates: 1) the number of microvessels depends on the genetic effects and metabolic needs of the tissues; 2) the diameter of the vessel depends on the flow of blood flowing through it; 3) the thickness of the vascular wall depends on the magnitude of transmural tension [14]. At present, these provisions have been deciphered in detail. Some observations suggest that microcirculatory abnormalities, in particular, rarefaction, may not be a consequence, but the cause of hypertension. T. F. Antoniosetal. showed that structural rarefaction can be found already in the early stages of GB [3; 6]. Moreover, it was found in healthy individuals with a genetic predisposition to hypertension [11]. Thus, the primary anatomical disorders of the ICR, in particular the suppression of angiogenesis and the disturbance of the growth of microvessels, can underlie GB. Over the past 15-20 years and now, in studying the state of the microcirculation system in various
tissues, the laser Doppler flowmetry (DF) method has been widely used, which makes it possible to evaluate the level of tissue perfusion in general, as well as to give a detailed description of the state and regulatory mechanisms of blood flow MCR [1; 10]. The method is based on recording the dynamics of the blood flow in the MCR (proper fluorimetry) with the aid of the laser beam fabrication with further processing of the radiation reflected from the tissue, which is based on the Doppler effect. The doppler effect consists in changing the length of the wave of a low-frequency gallium-non-newgazer reflected from the blood cells, predominantly of erythrocytes, moving through surface microscopic vessels [20]. The fixed signal is proportional to the average velocity and the number of erythrocytes moving over a certain volume of tissue per unit time. In turn, the number of erythrocytes depends on the number of actively functioning capillaries [4]. The laser beam penetrates into the skin to a depth of up to 1.5 mm and provides information about the blood circulation in superficially located microdesodes [2]. The movement of erythrocytes in papillary capillaries of the skin, arterioles, venules and arteriovenous anastomoses of the superficial and middle layers is recorded [3]. The contribution of capillaries to the combined DF-signal is less than 10%, microcapsules of sub-papillary weaving is more than 90% [10]. Microcirculation disorders become one of the leading links in the pathogenesis of hypertension, contribute to the onset and progression of target organ damage - LV myocardial hypertrophy, hypertensive nephropathy, cerebrovascular pathology [4]. Reducing the density of microvessels in combination with changes in the rheological properties of the blood helps to reduce tissue perfusion and oxygen transport to tissues, and also leads to an increase in peripheral resistance and blood pressure [2]. On this basis, AH can be considered as a progressive ischemic syndrome with the involvement of macro- and microcirculation [20]. The various links of the MCR are capable of responding to stimuli as a single integral system that can adapt to the changing conditions of tissue replacement and is characterized by great plasticity. Therefore, a detailed study of the structure and function of one area accessible to the researcher may well provide an idea of the state of microcirculation in the whole [1].
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