Measuring Blood Pressure | Class X

  • Blood pressure is the pressure against the wall of blood vessels produced by the discharge of blood into them by contraction of the left ventricle.
  • The blood pressure is high in the arteries.
  • It gradually drops in the capillaries, and becomes very low in the veins.
  • Fluids always flow from area of high pressure to areas of lower pressure.
  • Blood pressure is generally measured by determining the millimetres of mercury (Hg) displaced in a pressure gauge called sphygmomanometer.
  • A common sphygmomanometer has an inflatable bag-like cuff, a compressible bulb, a screw for releasing pressure, a mercury manometer and two rubber tubes connecting the bulb and manometer with cuff.
  • Cuff is wrapped around the upper arm and is rapidly inflated with a hand pump.
  • The sound of blood flow can be heard through a stethoscope.
  • This sound of blood rushing through the arteries at peak pressure is due to ventricular contraction.
  • This indicates systolic blood pressure (120 mm of Hg). A screw is used for releasing pressure, and pressure in cuff continues to drop.
  • The sound fades, until it stops. The reading indicates the diastolic blood pressure (80 mm of Hg).
  • The normal blood pressure of a human being is written as 120/80.

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