Eli5: how does the blood pressure cuff determine your blood pressure so accurately?
In: 200
The cuff has a simple pressure gauge in it that measures the pressure in the cuff. It’s basically the same as a tire pressure gauge.
The cuff is inflated to a pressure greater than your systolic blood pressure (pressure when the heart is pumping). Because the pressure in the cuff is higher than the blood pressure, it squeezes off the blood vessels and the pulse stops.
As air is let out and the pressure in the cuff drops, the person listens through the stethoscope. When the cuff pressure is equal to the blood pressure the vessels will stop being compressed and the pulse will return. The reading on the cuff is the systolic pressure.
Air is contained to be let out of the cuff causing the cuff pressure to continue to drop. But because the cuff pressure is still greater than the blood pressure when the heart is not pumping (diastolic) and the sound through the stethoscope indicates the blood flow is restricted.
The pressure at which the flow sound returns to normal is the lower (diastolic).
It all works because the pressure in the cuff and the pressure in the blood vessels close to the cuff are assumed to equalize. It’s like squeezing off flow in a garden hose. If you apply a pressure greater than the water pressure in the hose, you will stop the flow. As you release the pressure, at exactly an equal pressure, flow will return By reading the pressure in the cuff, you assume you are reading the pressure in the blood vessels.
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