Biophysical features of an aorta

Under action of the blood which is thrown out in a systole by left ventricle, there is a stretching of aortic w all possessing elastic properties. At changes of pressure of blood in a vessel its gleam changes mainly, and the length remains practically constant. In the moment of a systole diameter of an aorta increases approximately for 10 % concerning its diastolic values. The factor of elasticity is defined basically by elastic fibers, but in aortic wall there are collagenic fibers. On histologic preparations of an aorta collagenic fibers have wavy (goffered) form caused by their free (friable) stacking among other structures, staying in not deformed condition. Under action of increase of a blood pressure in physiological limits collagenic fibers only are straightened, but not stretched. Owing to collagenic fibers wall of arteries of the healthy person are not destroyed even at increase of a blood pressure at 5-10 time. Hence, collagenic fibers provide to an arterial wall not elasticity, and rigidity and durability.

On the contrary, elastic fibers of aortic walls are stretched at usual changes of a blood pressure during a systole of heart. In elastic fibers there is a force of elasticity according to Hooke's law. Module Junga of elastic fibers is factor of proportionality between force of elasticity and size of a stretching of a wall of an aorta at increase blood pressure, equal (0,4-1,0) ∙10⁶ pascal. In physiological conditions dependence of force of elasticity elastic fibers of an aorta from a degree of a stretching is exponential. At stronger stretching linear dependence is established, strongly stretched elastic fibers are broken off. Elasticity of aortic wall causes occurrence and distribution of pulse-wave on a wall of arteries. Pulse-wave extends from a place of the occurrence up t o capillaries where fades.

The doctor receives a general characteristic of pulse-wave at palpation of artery, registration of a curve of arterial pulse, which is called sphygmogram, gives fuller data. Fig.5.Sphygmogram, written down by two sensors of pulse fluctuations, located in different points of an arterial channel. Speed of pulse-wave in walls of investigated arteries can be defined having written down sphygmograms in two points of an artery and having measured shift of a phase between them. Speed of pulse-wave in an aorta 4-6 m/sec, and in a radial artery - 8-12 m/sec. Rigidity of arteries raises at scleroses changes. Speed of pulse waves increases with age. Than above elasticity of an arterial wall, the more amplitude of fluctuations of a blood pressure in an aorta and large arteries. Fluctuations of a blood pressure with the big amplitude create additional loading on heart and strengthen deformation vascular wall. More complex is venous pulse - fluctuations of walls of venous vessels. It arises in the veins running into auricles, and extends in a direction to capillaries. Amplitude of venous pulse below, than arterial, that is caused first of all by smaller elasticity of environments of venous vessels. The curve of venous pulse is called phlebogram. Hence, from heart to a capillary channel move towards each other two pulse waves (arterial and venous), and both die away in capillaries. Hence, two pulse waves move towards each other from heart to a capillary channel (arterial and venous), and both die away in capillaries.

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