Sphygmomanometer

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Image:Sphygmomanometer.jpg Image:Electronic tensiometre.jpg A sphygmomanometer or blood pressure meter is a device used to measure blood pressure, comprising an inflatable cuff to restrict blood flow, and a manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just starting, and at what pressure it is unimpeded.

The word comes from the Greek sphygmus (pulse), plus the scientific term manometer (pressure meter). The device was invented by Samuel Siegfried Karl Ritter von Basch. Scipione Riva Rocci, an Italian physician, introduced a more easily used version in 1896. Harvey Cushing discovered this device in 1901 and popularized it.

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. Image:BloodPressure.jpg

1 Operation
2 Significance
3 Types
4 See also
5 Patents

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Operation

The cuff is usually placed around the upper left arm, at roughly the same vertical height as the heart while the subject is in an upright 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.

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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.

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Types

There are two types:

Digital (modern, easy to operate and practical in noisy environment. Have not been validated for all patient groups, and can give very inaccurate readings).
Manometric (old fashioned, though more precise). Those that use mercury columns have been banned in some places. Aneroid types are still in common use.

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