Measurement of pressure of blood

Measurement of pressure in a blood vessel can be made by introduction in a vessel of the hollow needle connected by a rubber tube with a manometer. The similar way is used in experiment on animals.

In a surgical practice direct measurement of pressure in cavities of heart is made by a method of catheter, entering through one of large vessels thin polyethylene probe on which end there is a tiny electric manometer

In clinic the indirect bloodless way of measurement of a blood pressure is applied. Pressure is measured, which is necessary for putting outside to compress an artery before the termination in it of a current of blood. This pressure is rather close to pressure of blood in an artery. Measurement is usually made on a humeral artery above an elbow bend (fig.3)

Compression of an artery is carried out by means of a cuff M (the flat rubber chamber in fabric cover), which wrap up around of a shoulder and, working as supercharger Н, fill air to necessary pressure. The size of pressure is defined on manometer Р connected to a cuff. The method of measurement of arterial pressure on Korotkov is most widespread. This method is based on auscultation of the sounds which have arisen at passage of blood through an artery compressed by a cuff. For measurement of pressure it is necessary to do following actions:

To put on a cuff па a shoulder of the patient, to grope pulse of a humeral artery a little above an elbow bend and inside from a two-headed muscle.

To put to this place a stethoscope.

To close the crane of a supercharger and, rhythmically compressing and releasing a pear, to fill a cuff with air up to pressure upon 10-20 mm of a mercury column above at what pulse ceases to be probed on a beam artery.

Slowly rotating the final screw of a supercharger, pressure gradually is reduced in a cuff and sounds appearing in a stethoscope are listening.

The parity between change of pressure p in a cuff and «Korotkov's tones» it is shown schematically on fig.4.

P_S - systolic (in norm of 100-120 mm of a mercury column), P_d - diastolic (70-80 mm of a mercury column) pressure.

While the artery is compressed completely, any sounds are not listened. At decrease in a cuff of pressure start to be listened ­ the tones is called initial. There is a pulse on a beam artery. These tones are caused by vibration of walls of an artery directly behind a cuff under action of pushes from portions of blood which break through the site of a vessel compressed by a cuff only during the moments of a systole of heart (the maximal pressure). Indications of a manometer, at the first occurrence of tones, correspond maximal or systolic pressure. At the further pressure decrease in a cuff tones are supplemented with noise which becomes sometimes stronger than tones.

These noises are caused, apparently, by turbulent current of blood: through site of an artery partially squeezed by a cuff. Then noise abate and in a phonendoscope only tones named consecutive again are listened. These tones quickly weaken, and the sound phenomena stop. It occurs at full restoration of a gleam of an artery and an establishment of normal laminar current of blood. Indications of a manometer, during the moment of sharp reduction of loudness of tones, correspond minimal or diastolic to pressure.

The device for measurement of arterial pressure consists of three basic parts:­ cuff of M, supercharger Н and a manometer Р.

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