What is a Sphygmomanometer?

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  • Written By: Adam Hill
  • Edited By: Bronwyn Harris
  • Last Modified Date: 06 January 2020
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Among the many common tools used in a doctor’s office is one which we’re all familiar with, but whose real name is little-known. That device is the sphygmomanometer, which is used to measure blood pressure. The sphygmomanometer has been in wide use since the early 20th century, and consists of a cuff placed around the arm, as well as a device to measure the pressure at which blood flows freely, and the pressure at which blood flow is restricted.

When a sphygmomanometer is used, the cuff is inflated, usually around the upper arm, and the pressure is gradually released. A digital sphygmomanometer often operates at the touch of a button, and the blood pressure data is displayed on a digital screen. Many manual sphygmomanometers are also still in use, which usually require a medical professional to operate correctly.

In a manual device, the pressure is displayed as the height of a column of mercury in a tube. As the cuff is manually inflated, the height of the column increases, and then decreases as the pressure is released. While the cuff deflates, the doctor usually listens with a stethoscope to the main artery of the arm.


When the flow of blood begins to flow again after being stopped by the cuff, there begins to be a rushing or pounding sound that the doctor is able to hear through the stethoscope. The pressure at which this occurs is noted, and is called the systolic pressure. The cuff is allowed to further deflate, and the pressure at which the sound is no longer audible is also noted, and is called the diastolic pressure. These two values are the pair of numbers that are recognizable as a blood pressure value.

It is important that a person’s blood pressure be measured when he is relaxed, otherwise the reading will be falsely elevated. Hormones such as adrenaline can increase blood pressure dramatically by constricting blood vessels. A person who has just been severely startled, for example, will have an elevated blood pressure compared to someone who is watching television. Accurate readings are essential to determine the health of the heart and therefore the rest of the body.

The use of a manual sphygmomanometer, like many things in medicine, takes some practice before you can consistently get correct readings. For those with hypertension, however, this may be a valuable skill, since it is important in that case to measure your blood pressure frequently. Apart from the convenience involved, some patients get nervous when their blood pressure is taken by a doctor, sometimes referred to as lab coat syndrome. This can throw off the reading, so being able to measure your own blood pressure at home is not only convenient but also medically relevant.


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