SPEED OF THE BLOOD-GROOVE

From Big Medical Encyclopedia

SPEED OF THE BLOOD-GROOVE — intensity of the movement of blood in various departments of the blood circulatory system. It can be expressed by two indicators: in the form of a so-called volume flow (volume S. to.), i.e. amounts of the blood proceeding through cross-section of a vessel for a unit of time in l/min or ml/sec., and mass flow (mass S. to.), i.e. the mass (weight) of the same blood in kg/min. or g/sec. Between volume S. to. (Q) and mass (Q m ) there is a ratio: Qm = pQ, in Krom r — density of blood. Besides, there is a concept «linear S. to.» reflecting speed of the movement of specific particles of blood, including its uniform elements and the substances transferred by it; it characterizes the movement of a particle of a flow for a unit of time in m/s measured in a specific point. Linear S. to. it is not identical on all section of a vessel — at a wall it is equal to zero, in the center is maximum since the blood stream is carried out by hl. obr. due to movement of the mass of blood located about an axis of a vessel. Linear S.' distribution to. on the section of a vessel call a profile of speeds. It depends on character of a current of blood on a vessel — whether it is laminar when separate layers of blood do not mix up (see. Hydrodynamics ), what is peculiar to the majority of vessels, or turbulent, at Krom layers of blood chaotically mix up that is observed in large vessels and vessels with strongly broken smoothness of a bed, and also at small viscosity of blood (see. Viscosity ). In the first case the so-called parabolic profile of speeds takes place (fig. 1, a), in the second case it comes nearer to plane-parallel (fig. 1, b). Therefore linear S.'s value to. cannot reflect intensity of a blood-groove in any one point of section of a vessel. Average can serve as such characteristic on the section of a vessel of S. to. (Wcp) or the speed of an ideal plane-parallel flow, on productivity equivalent to a real current, both laminar, and turbulent. The last is expressed by a formula:

W Wednesday = Q/S, where S — the area of internal section of a vessel.

Fig. 1. The diagrammatic representation of section of blood vessels with various profiles of speeds of a blood-groove: about — a parabolic profile of speeds of a blood-groove in a laminar flow; — a plane-parallel profile of speed of a blood-groove in a turbulent flow; shooters specified the direction of a blood-groove, length of an arrow specifies the size of speeds of a blood-groove in this site of a vascular bed.

The movement of blood on any site of a vessel is carried out under the influence of swing pressure on the ends of this site. Page to. depends therefore on the size of pressure operating in a vessel. For streamline flow volume S.'s communication to. and the operating pressure it is described by Poiseuille's formula (see. Hemodynamics ): volume S. to. it is proportional to the swing pressure operating on a flow. This dependence reflects the nature of the movement of blood in peripheral vessels. For a turbulent flow the same communication is described by Torricelli's formula: volume S. to. it is proportional to a square root from swing pressure. It is characteristic of a current of blood in heart, the central vessels and of cases when Reynolds's number (the relation of the work of fluid density, speeds of its current and diameter of a vessel, on Krom it flows, to liquid viscosity) surpasses critical value — 2300.

Fig. 2. The chart reflecting rate of volume flow of a blood-groove in various bodies and fabrics at rest (height of the painted-over part of a column) and at the maximum vasodilatation (height of all column) at the person weighing about 70 kg: 1 — sialadens; 2 — kidneys; 3 — a myocardium; 4 — digestive tract; 5 — skin; 6 — a liver (a hepatic artery); 7 — the central nervous system; 8 — skeletal muscles; 9 — hypodermic cellulose.
Fig. 3. The schedule reflecting the total area of cross-section of blood vessels (dashed line), average peripheral speed of a blood-groove (it is designated by points) and size of blood pressure (solid line) in different departments of vascular system at rest.

Volume, mass and linear S. to. are various on intensity in different vessels that is connected with branching of vascular system, its structure and basic purpose in this or that area. In exchange vessels of S. to. is defined by need to provide effective transcapillary exchange between blood and an intercellular lymph at very small extent of these vessels (0,6 — 1,0 mm), in transport vessels — to deliver blood to the periphery and again to return it to heart with the minimum metabolic cost, having avoided aggregation of uniform elements. The greatest S. to. in mouths of the arteries adjoining heart (an aorta and a pulmonary artery), it reflects total consumption of blood an organism and is known as the second or minute volume of heart measured respectively in l/sec. and l/min (see. Blood circulation, physiology ). Intensity of a blood-groove in various bodies and body tissues at rest and at their maximum blood supply is various (fig. 2). The big difference is observed also in linear S. to. in various departments of vascular system (fig. 3).

The considered characteristics reflect a blood stream as process stationary with uniform motion of blood. The real current of blood on the blood circulatory system differs, however, irregularity and has the expressed dynamic character. More irregularity is expressed in heart and in the vessels adjoining it (the movement in them happens falteringly, to stops). In the vessels remote from heart, blood moves continuously, but with the pulsations decreasing in the direction to the periphery. In capillaries and peripheral veins the current of blood is close to uniform. Uniformity of the movement of blood on exchange vessels — to capillaries (despite the discrete nature of pumping function of heart) has important biological value as a condition of a continuity and constancy of exchange. To the movement of blood in transport vessels — arteries and large veins — irregularity of a blood-groove is not essential.

Primary link where dynamics of an arterial blood-groove forms, the ascending part of an aorta is. Here the blood stream in a diastole and in the period of isometric contraction of a left ventricle is absent. At the same time pressure in view of ongoing food of the mpkrotsir-kulyatorny pool continuously decreases. From the beginning of a sphygmic interval of S. to. quickly accrues, causing reservation of blood in arterial system for the subsequent its expense in a diastole. During this period called by the period of bystry exile on the pressure curve anacrotic rise forms. S.'s maximum to. comes in 0,05 — 0,08 sec. from the beginning of exile and is on time close to a maximum of rate of pressure rise. By the time of approach of a maksrshum of pressure corresponding to balance between inflow and outflow of blood, S. to. already it is considerably reduced, and in other part of a sphygmic interval, the so-called period of the reduced exile, it lags behind the speed of outflow and by its end reduces to zero. In view of short duration of bystry exile (0,09 — 0,12 sec.) in comparison with duration of a cardial cycle the average speed of a blood-groove during this period by 7 — 10 times surpasses the second volume of heart, the peak speed of exile surpasses it in tens of times. The beginning of the diastolic period on curve S. to. it is designated by the negative clove caused by a small reversed current of blood at the time of valve reseat of an aorta. Similar character has a blood stream and in a pulmonary artery.

Exile of blood the weakened heart is made less vigorously, the peak of speed comes later, amplitude decreases, is especially strong at insufficiency of ventricles.

Opposite changes are observed at persons with a high functional reserve of heart. At aortic incompetence their S. is increased to. in a sphygmic interval, but in other part of a cardial cycle, especially during the early diastolic period, on curve S. to. the negative wave correlating on amplitude with degree is registered regurgitations (see).

Curve S. have sharply excellent form to. in coronary arteries that is caused by considerable or full crossclamping of intramural vessels in a systole and their disclosure at relaxation of a myocardium. Also curve S. differ in a special configuration to. in venas cava, the blood reflecting dynamic structure of venous return to heart. Filling of the right auricle is carried out falteringly in several phases with three peaks corresponding to phases of presystolic, systolic and post-systolic aspiration of blood.

S.'s measurement to. it is made by different methods. The leading value in a wedge, practice has measurement of minute volume of heart (see. Blood circulation , Pletizmografiya , Reografiya ). The ultrasonic doppler-takhografiya is eurysynusic (see. Ultrasonic diagnosis ). The method allows to probe from a body surface an ultrasonic beam the vessels located in the depth of an organism. Accuracy of a method depends on the accuracy of orientation sensor (see). The same problem in vascular surgery is successfully solved with use of electromagnetic flowmeters, sensors to-rykh are imposed on not opened, but a naked vessel (see. Blood circulation, methods and devices for a research ).

In pilot studies the gages of a blood-groove demanding for connection of the device of section or a puncture of a vessel (drop, bubble, needle pl shchetinkovy and other floumetra), differing in the high static and dynamic precision, simplicity and reliability kept the value.


Bibliography: Gayton A. Physiology of blood circulation, Minute volume of heart and its regulation, the lane with English, M., 1969; Johnson P. Peripheric circulation, the lane with English, M., 1982; 3 and-retsky V. V., etc. Electromagnetic floumetriya, M., 1974; Caro K., etc. Mechanics of blood circulation, the lane with English, M., 1981; R and sh m of e p P. Dynamics of cardiovascular system, the lane with English, M., 1981; With and in and c to and y H. H. Biophysical bases of blood circulation and clinical methods of studying of a hemodynamics, L., 1963; Modern methods of a research of functions of cardiovascular system, under the editorship of E. B. Babsky and V. V. Larin, M., 1963; Physiology of blood circulation, Physiology of heart, under the editorship of E. B. Babsky, etc., L., 1980; Folkov B. and Neil E. Blood circulation, the lane with English, M., 1976.


E. K. Lukyanov, V. S. Salmanovich.

Яндекс.Метрика