Avtor/Urednik		Poredoš, Pavel
Naslov		Hemoreologija in mikrocirkulacija
Prevedeni naslov		Haemorheology and microcirculation
Tip		članek
Vir		Med Razgl
Vol. in št.		Letnik 35, št. Suppl 2
Leto izdaje		1996
Obseg		str. 39-46
Jezik		slo
Abstrakt		In addition to pressure gradient and the geometry of a segment of a blood vessel, the composition of blood has a decisive influence on blood flow, especially in microcirculation, since the viscosity or fluidity of blood depend on its composition. In physiological conditions, blood flows easily through the thinnest capillaries, in spite of its complex composition, even though the diameter of individual blood cells is greater than the diameter of the capillaries. These almost ideal rheological properties of blood are based on the exceptional ability of blood cells, especially erythrocytes, to assume an ideal ellipsoid form and thus have a smaller diameter while passing through small blood vessels. In normal circumstances, the erythrocyte membrane also rotates while passing through small blood vessels; erythrocytes therefore travel more rapidly than the plasma in which they are suspended, and keep to the central part of blood flow which is the fastest. This causes a hemodynamic dilution of blood in the area of capillaries which significantly reduces the viscosity of blood. Rheological properties of blood can deteriorate significantly it a reduction in perfusion pressure occurs or if the composition of blood changes (increased fibrinogen concentration and increased hematocrit). In such conditions, blood flow through capillaries slows down, erythrocytes are not deformed and they become rigid. This has an additional negative influence on blood flow. A positive feedback loop is established which can lead to a complete stagnation of blood flow in microcirculation. Hemorheological changes can be found in different conditions and can nowadays be influenced with various treatment procedures. In hypoperfusion, a systemic increase of perfusion pressure and revascularisation procedures are used. (Abstract truncated at 2000 characters.)
Izvleček		Na tok krvi, zlasti v območju mikrocirkulacije, poleg gradienta tlaka in geometrije žilnega segmenta odločilno vpliva sestava krvi. Od sestave krvi je namreč odvisna njena viskoznost in tekočnost. V fizioloških pogojih kri kljub zapleteni sestavi z lahkoto teče tudi skozi najtanjše kapilare, četudi je premer posameznih krvnih celic večji, kot je premer kapilare. Te skoraj idealne reološke sposobnosti krvi temeljijo na izjemnih lastnostih krvnih celic, zlasti eritrocitov, da pri prehodu skozi drobne žile zavzamejo idealno elipsoidno obliko in s tem pomembno zmanjšajo svoj premer. V normalnih razmerah e pri prehodu skozi manjše žile membrana eritrocita tudi vrti, zato eritrocit potuje hitreje kot plazma, v kateri se nahaja, in zavzame središčni del toka krvi, ki je najhitrejši. Posledica je hemodinamska dilucija krvi v območju kapilar, ki pomembno zmanjša viskoznost krvi. Reološke lastnosti krvi se lahko pomembno poslabšajo, če pride do zmanjšanja perfuzijskega tlaka ali če se spremeni sestava krvi (zvečane koncentracije fibrinogena in hematokrita). V takih razmerah se tok krvi skozi kapilare upočasni, eritrociti se ne deformirajo in postanejo togi. To dodatno negativno vpliva na tok krvi in se vzpostavi pozitivna povratna zveza, ki lahko pripelje do popolnega zastoja krvi v mikrocirkulaciji. Hemoreološke spremembe najdemo pri različnih bolezenskih stanjih, nanje pa lahko danes že vplivamo z različnimi zdravilskimi postopki. Pri motnjah prekrvitve se poslužujemo sistemskega zvečanja perfuzijskega tlaka in revaskularizacijskih posegov, pri zvečanih koncentracijah hemoglobina in eritrocitov hemodilucije in pri togosti krvnih celic in nesposobnosti njihove deformacije zdravilnih substanc, ki zvečujejo prožnost teh celic in s tem izboljšujejo hemoreološke razmere.
Deskriptorji		MICROCIRCULATION HEMORHEOLOGY BLOOD VISCOSITY HEMATOCRIT