Sphygmomanometer (blood pressure cuff)
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. 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.
Sphygmomanometer is an instrument for measuring blood pressure, particularly in arteries. The two types of sphygmomanometers are a mercury column and a gauge with a dial face. The sphygmomanometer in most frequent use today consists of a gauge attached to a rubber cuff which is wrapped around the upper arm and is inflated to constrict the arteries.
A blood pressure reading consists of two numbers: systolic and diastolic. Systolic refers to systole, the phase when the heart pumps blood out into the aorta. Diastolic refers to diastole, the resting period when the heart refills with blood. At each heartbeat, blood pressure is raised to the systolic level, and, between beats, it drops to the diastolic level.
The cuff is placed around the upper arm, at roughly the same vertical height as the heart while the subject is in a sitting person. 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.
With the cuff inflated with air, a stethoscope is placed over an artery (the brachial artery) in the crook of the arm. As the air in the cuff is released, the first sound heard through the stethoscope marks the systolic pressure. As the release of air from the cuff continues, a point is reached when the sound diminishes and then is no longer heard. The point where the sound disappears marks the diastolic pressure. The blood pressure reading might show the systolic and diastolic pressures to be, for example, 120 and 78mm of mercury (Hg) respectively -- written 120/78 and said to be "120 over 78." A typical blood pressure reading for an adult might, in fact, be 120/78. Readings vary depending on age and many other factors. Children and adults with smaller or larger than average-sized arms may need special-sized pressure cuffs.