Definition of speed of blood-groove

There are some methods of definition of speed of a blood-groove. We shall consider physical bases of two of them. The ultrasonic method (ultrasonic flowmeter survey) is based on Doppler’s effect. The signal from the generator 1 of electric fluctuations of ultrasonic frequency acts on a radiator of ultrasound 2 (look figure) and on the device of comparison of frequencies 3. The ultrasonic wave 4 gets into a blood vessel 5 and is reflected from moving erythrocytes 6. The reflected ultrasonic wave 7 gets in the receiver 8 where it will be transformed to electric fluctuation and amplifies. The strengthened electric fluctuation gets in the device 3. Here the fluctuations, the falling and reflected waves are compared, and is allocated Doppler shift of frequency in the form of electric fluctuation: U=U_ocos2πν_Dt

From this formula it is possible to define speed erythrocytes:

In large vessels speed erythrocytes depends on their arrangement concerning an axis: erythrocytes, located close to an axis, move with greater speed, and erythrocytes located close to a wall of a vessel move with smaller speed. The ultrasonic wave can be reflected from different erythrocytes; therefore Doppler shift has an interval of frequencies. Doppler’s effect allows to define average speed of a blood-groove and speed of movement of various layers of blood.

The electromagnetic method (electromagnetic flowmeter survey) measurements of speed of a blood-groove is based on a deviation of moving charges in a magnetic field. Blood is electrically neutral system, it consists from positive and negative ions. Hence, moving blood is a stream of the charged particles which move with a speed v. Force in a magnetic field with induction B acts on a moving electric charge q. F=qvВ

If a charge negative, force is directed to opposite of vector product vВ.

The forces operating from a magnetic field on opposite charges are directed to the opposite parties. The positive charge accumulates about one wall of a blood vessel, about another - negative. Redistribution of charges on section of a vessel will cause occurrence of an electric field. This physical phenomenon refers to effect of the Hall.

Pressure U_H (Hall’s pressure) depends on speed v ofmovements of ions, i.e. from speed of blood. Thus, measuring this pressure, it is possible to define and speed of a blood-groove. Knowing section S of a vessel, it is easy to calculate volumetric speed of a blood-groove: Practically it is more convenient to use in this method a variable magnetic field (see fig.). It leads to occurrence variable Hall’s pressure U_H which then amplifies and measured.

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