pls explain the diagram on page 107 of ncert textbook [ relating to blood pressure]

Asked by sonaisha | 23rd Mar, 2009, 01:40: PM

Expert Answer:

The diagram shows the process of measurement of blood pressure using sphygmomanometer.

Blood pressure measurement through the sphygmomanometer is one of the most common ways of monitoring blood pressure. It requires an inflatable cuff, a dial of measurement and a stethoscope.

The bladder is inflated until the cuff compresses the artery of the arm, the blood does not pass anymore: the stethoscope perceives no noise.

Then the cuff is deflated slowly, the blood goes through the artery again: the stethoscope perceives a noise and the value of the blood pressure is read at the same time on the dial. The blood pressure measured at this moment is the maximal blood pressure, the systolic blood pressure.

The cuff continues to deflate slowly. The blood passes again and the stethoscope perceives a noise.

The more the cuff deflates and the less audible the noise will be by the stethoscope, until it disappears completely: the blood pressure is read on the dial and defines the minimal, i.e. the diastolic blood pressure.


The principle of measurement consists in recording not the blood pressure directly in the artery but the arterial counter pressure by squeezing the artery on which the pressure is measured.

The doctor uses a cuff (or an arm-band) which will be gradually filled with air to press the artery below. The doctor listens to, using his stethoscope, to the noise emitted by blood at the time of its passage in the artery.


When the band is sufficiently inflated to compress the artery that is below, blood cannot pass any more and the doctor thus does not perceive any noise. Then, the cuff is gradually deflated and the noise now perceived defines the maximal blood pressure (systolic blood pressure). As the band carries on its deflation, the noise of the artery disappears again and the physician measures the pressure corresponding now to the minimal (diastolic blood pressure).

Answered by  | 25th Mar, 2009, 07:05: AM

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