Anonymous asked in Science & MathematicsPhysics · 1 month ago

Physics help?

How do the concepts of hydrostatic pressure and some other Physics laws are involved in the working procedure of an analogue sphygmomanometer?

1 Answer

  • 1 month ago
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    If the body tissues can be modelled as a fluid then the pressure within the tissues is the same everywhere ( an approximation ) the cuff covers a significant area to make this approximation realistic.  The pressure in the cuff is increased until all blood flow ceases ( lack of pulse) therefore the pressure in the cuff must be equal to the MAXIMUM blood pressure.  ( systolic?).

    A tube connects this to a balanced column of mercury.  Again the pressure is the same at all points within the tube and it acts on the surface of the mercury.

    This pressure causes the mercury to move up a tube. The weight of the mercury in the tube creates an increase in pressure with depth.  So that the pressure at the bottom ( connected to the cuff) is greater than the pressure at the top ( connected to the air ). The difference is the pressure of the blood.

    Now air is gradually released and the pulse resumes.  However as the blood flows under the pressure of the cuff at some parts of the cycle the blood pressure is insufficient so the flow stops at some parts of each heartbeat.  This can be detected audibly or by feel.  When the flow is continuous without a stop then the pressure in the cuff is equal to the lowest pressure in each cycle of the heart ( diastolic? )  The two readings give a fair measure of the performance of the heart and blood flow.

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