Sphygmomanometer

The sphygmomanometer, commonly called a blood pressure meter, monitor or gauge, measures blood pressure using an inflatable rubber cuff wrapped around the upper arm, connected to a pressure-measuring unit - traditionally a column of mercury on a calibrated scale, or in newer designs a mechanical dial or a digital sensor. In the classic manual technique, the cuff is placed about 3 cm above the elbow and the stethoscope's resonator is positioned over the brachial artery at the crook of the elbow. The cuff is quickly inflated to around 180 mm Hg, well above the point where it stops blood flow in the artery, and then slowly deflated. As the pressure falls, the moment a rhythmic 'whooshing' sound of returning blood flow is first heard marks the systolic pressure - the peak pressure generated when the heart's ventricles contract. As deflation continues, the point at which the sound disappears entirely marks the diastolic pressure - the lowest pressure, recorded when the ventricles are relaxed between beats. A normal reading is written as 120/80 mmHg (120 systolic over 80 diastolic). There are two broad types of sphygmomanometer: manual instruments, which include the mercury type (accurate and needing no calibration, since it reads height of a mercury column directly) and the aneroid type (a mechanical dial mechanism that does need periodic calibration checks); and digital sphygmomanometers, which use an electronic oscillometric sensor to detect systolic and diastolic pressure automatically, require no manual calculation, and can be operated without special training. Clinically, blood pressure readings are used to diagnose conditions such as hypertension (high blood pressure) and hypotension (low blood pressure), to assess the overall state of blood circulation, and to gauge how well the heart is functioning. One recognised quirk of …