Sphygmomanometers indicate a patient's blood pressure by measuring mean arterial pressure and then calculating systolic and diastolic measurements. The device is composed of a dial, pump, cuff and valve. Once the cuff is inflated, it applies pressure to the brachial artery.
A medical professional wraps the cuff around a patient's upper arm, inflates the pump, places the chestpiece of a stethoscope under the cuff and then slowly releases the pressure by adjusting the valve. As pressure is released, the systolic measurement is noted when the blood begins to flow again. The medical professional is able to detect this by sound through the stethoscope. The diastolic reading is taken at the point at which the heart relaxes and blood flow returns to normal, which is also detectable by sound.
When the systolic and diastolic measurements are high, it indicates the heart is pumping excessively hard, a sign that blood vessels are constricted or partially clogged with plaque. Other causes of blood vessel constriction include high levels of adrenaline.
Samuel Siegfried Karl Ritter von Basch invented the sphygmomanometer in 1881. The device's name is derived from the Greek world "sphygmos," which means "pulse," and the scientific term "manometer," which refers to a means of measuring pressure.