Clinical Hemorheology and Microcirculation 30 (2004) 461–462 IOS Press
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Hemorheological disorders in the microcirculation following hemorrhage T. Sordia, J. Tatarishvili, M. Varazashvili and G. Mchedlishvili Microcirculation Research Center, I. Beritashvili Institute of Physiology, 14 Gotua St., 0160 Tbilisi, Georgia Tel.: +995 32 371016; Fax (Telecom Georgia): +995 32 00 11 53; E-mail:
[email protected] Abstract. We analysed hemorheological disorders in the microcirculation of intestinal mesenterium of adult laboratory rats following massive exsanguinations when the mean arterial pressure dropped and then the hemorrhagic shock developed in the animals. The mesenteric microcirculation was analysed by the Texture Analysis System (Leitz, Wetzlar): (a) diameters of the afferent arterioles, capillaries, and efferent venules; (b) the blood flow velocity; (c) microvascular blood flow changes (during the RBC aggregation); (d) local microvascular hematocrit; and (e) the transformation of capillaries into plasmatic microvessels. During development of the hemorrhagic shock we found that the blood flow velocity decreased in all microvessels, there was an increased RBC aggregation which gradually enhanced in the mesenteric microvessels’ lumen causing blood flow slowing down till appearance of stases. A part of the capillaries transformed into plasmatic vessels. Therefore the microcirculation demonstrated a significant decrease, this being related both to the lowered pressure gradient and to specific hemorheological disorders in the capillary networks. Keywords: Hemorheological disorders, microcirculation, hemorrhage
1. Introduction Vasomotor activity of capillary microvessels, being deprived of muscular elements in their walls, is a problem that was related to the classical works of Krogh [1] and Zweifach [3]. The first of them solved the problem positively, while the second has proved convincingly that the true vasomotor activity might be related only to muscular elements of the arteriolar and metarteriolar walls. Our perennial microcirculatory research [2] provided us with a firsthand experience of the capillary flow changes under various conditions. Our recent studies demonstrated a specific “vasomotor” activity of the capillaries, as well as a pronounced effect of the hemorheological disorders on the microvascular blood flow. 2. Methods Experiments were carried out with anesthetized white laboratory rats. Preliminary surgical procedure included tracheotomy and cannulation of the common carotid artery for recording of the systemic arterial pressure and for its monitoring at a necessary level in the course of the experiments. Abdominal cavity was opened by a sagittal cut and an intestinal loop was drowned out for microscopically investigation of microcirculation in the intestinal mesenterium. For analysis of the microcirculation the appropriate equipment of Leitz (Wetzlar) was applied including the “Ortoplan” binocular microscope. In the microcirculation we always identified the smallest arterioles 1386-0291/04/$17.00 2004 – IOS Press and the authors. All rights reserved
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and venules, as well as the thoroughfere channels and the remaining capillary networks. Diameters of specific microvessels were measured with linear micrometer eyepiece RZD-DO. Blood flow in the chosen microvessels was continuously recorded by using the telecamera adjusted to the microscope, and all the microcirculatory phenomena were investigated by using the video recorder (Panasonic NV-HS900) for their subsequent analysis. 3. Results The precapillary arterioles (initial diameter up to 20 µm) showed a regular constriction (by ca. 41%) while the capillaries adjoining to the venules, on the contrary, underwent increase of their diameter (by ca. 15%). The local hematocrit in the capillary network was significantly decreased, while up to 45% of the investigated microvessels became plasmatic (only with plasma, without RBCs). Simultaneously, the RBC aggregability became regularly enhanced in all the capillaries. Under these conditions the RBCs were grouped and had plasmatic interwals in-between occupying from 30 to 70% of the whole microvessels’ length. 4. Conclusion The regular constriction of arterioles during arterial hypotension is certainly a compensatory response to adapt the microcirculation to the lowered arterial pressure. The dilatation of the venous portions of the capillaries can be only an active vasomotor reaction under the conditions of the lowered intravascular pressure and constriction of the feeding arterioles. Very essential seem to be the blood rheological disorders in the capillary networks under the present conditions. The lowered hematocrit in the microvessels is certainly a result of a partial substitution of the circulating blood by the tissue fluid. As to the enhanced RBC aggregation leading to blood rheological disorders in the microcirculation, this could not be but a pathological response disturbing the blood fluidity in the microvessels. This latter phenomenon during arterial hypotension needs to be specially analysed, since it could have only a disturbing effect on the microcirculation under conditions of arterial hypotension, which was in evidence in the present studies. References [1] A. Krogh, The Anatomy and Physiology of Capillaries, Yale Univ. Press, New Haven, CT, 1922. [2] G.I. Mchedlishvili, Microcirculation of Blood: General Principles of Control and Disturbances, “Nauka” Publishers, Leningrad, 1989. [3] B.W. Zweifach, The distribution of blood perfusates in capillary circulation, Am. J. Physiol. 120 (1940), 23–35.
