A device for measuring blood pressure. An inflatable rubber cuff is placed round a limb (usually the arm), and inflated until the pulse (heard through a stethoscope) can no longer be detected. The cuff is then slowly deflated until the sound of the pulse can be heard again. The first sound heard reflects the pressure of blood in the arteries as the heart actively contracts (systole). As the deflation of the cuff continues, a second sound is heard, reflecting the resting pressure (diastole) within the arteries. The pressure is read off either electronically or direct from a column of mercury.
A sphygmomanometer or blood pressure meter is a device used to measure blood pressure, comprising an inflatable cuff to restrict blood flow, and a mercury or mechanical 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).
A sphygmomanometer usually consists of an inflatable cuff, a measuring unit (the mercury 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. 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. In this sense, they do not actually measure the blood pressure, but derive the readings.Digital oscillometric monitors are also confronted with “special conditions” for which they are not designed to be used : arterial sclerosis, arrhythmia, preeclampsia, pulsus alternans, and pulsus paradoxus.
Gallery
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Mechanical sphygmomanometer with aneroid manometer and stethoscope |
Digital sphygmomanometer |
Mercury manometer |
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