How Does a Blood Pressure Gauge Work?

A nurse checking the blood pressure of a patient.
A Sphygmomanometer is used to measure blood pressure, typically consisting of an inflatable rubber cuff applied to the arm and connected to a column of mercury next to a graduated scale. John Rensten / Getty Images

Your heart is an amazing pump. It works reliably for decades, and it safely pumps blood -- one of the trickiest liquids around. In the same way, your blood vessels are pipes. They take the output from the pump and distribute it throughout the body. A blood pressure gauge is simply a way to measure the performance of the pump and the pipes.

There are two numbers in a blood pressure reading: systolic and diastolic. For example, a typical reading might be 120/80. When the doctor puts the cuff around your arm and pumps it up, what he/she is doing is cutting off the blood flow with the pressure exerted by the cuff. As the pressure in the cuff is released, blood starts flowing again and the doctor can hear the flow in the stethoscope. The number at which blood starts flowing (120) is the measure of the maximum output pressure of the heart (systolic reading). The doctor continues releasing the pressure on the cuff and listens until there is no sound. That number (80) indicates the pressure in the system when the heart is relaxed (diastolic reading).


If the numbers are too high, it means that the heart is having to work too hard because of restrictions in the pipes. Certain hormones, like adrenaline (which is released when you are under stress) cause certain blood vessels to constrict, and this raises your blood pressure -- if you are under constant stress, your blood pressure goes up, and it means that your heart has to work too hard. Other things that can increase the blood pressure include deposits in the pipes and a loss of elasticity as the blood vessels age.

High blood pressure can cause the heart to fail (from working too hard), or it can cause kidney failure (from too much pressure).


Sphygmomanometer FAQs

What is a digital sphygmomanometer?
A digital sphygmomanometer is an automated device that gives you a blood pressure reading without the need for a cuff or having to listen to the sound of blood flow.
How do sphygmomanometers work?
A sphygmomanometer is a specially designed device that is used to measure the blood pressure of individuals. It is made of an inflatable rubber cuff that's wrapped around the person's arm. Air is pumped into the cuff, and the blood that begins to flow past is measured, which equals to the arterial systolic pressure.
Why is it called a sphygmomanometer?
The sphygmomanometer was invented by Scipione Riva-Rocci, an Italian physician, in 1896. The first part of the name has Greek origins and means “the pulse”. The second part of the name means “a device used for measuring pressure.”
Do sphygmomanometers contain mercury?
No. Sphygmomanometers do not contain any mercury, especially if you are using an electronic or aneroid device. A mercury-free sphygmomanometer is considered to be safer for patients and the environment.
What are the two main types of sphygmomanometers?
The two main types of sphygmomanometers include manual and electric. The electric model is able to measure the blood pressure automatically, while in the manual version, pressure needs to be pumped into the sleeve.