Sphygmomanometer
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A sphygmomanometer is an inflatable cuff used to measure blood pressure. The word is derived from the Greek sphygmus (pulse), plus the scientific term manometer, the device was introduced by Scipione Riva Rocci, an Italian physician in 1896.
A sphygmomanometer usually consists of an inflatable cuff, a measuring unit (the manometer), a tube to connect the two, and (in models that don't inflate automatically) an inflation bulb also connected by a tube to the cuff. The inflation bulb contains a one-way valve to prevent inadvertent leak of pressure while there is an adjustable screw valve for the operator to allow the pressure in the system to drop in a controlled manner.
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Operation
The cuff is placed around the upper arm, at roughly the same vertical height as the heart while the subject is in a sitting position. The cuff is inflated until the artery is completely occluded. Listening with a stethoscope to the brachial artery at the elbow, the examiner slowly releases the pressure in the cuff. As the pressure in the cuffs falls, a "whooshing" or pounding sound is heard (see Korotkoff sounds) when bloodflow first starts again in the artery. The pressure at which this sound began is noted and recorded as the systolic blood pressure. The cuff pressure is further released until the sound can no longer be heard and this is recorded as the diastolic blood pressure.
Significance
The peak pressure in the arteries during the cardiac cycle is the systolic pressure, and the lowest pressure (at the resting phase of the cardiac cycle) is the diastolic pressure.
Types
There are two types:
- Digital (modern, easy to operate and practical in noisy environment).
- Manometric (old fashioned, though more precise). Since these usually use mercury they have been banned in some places.