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How Does a Blood Pressure Cuff Work?

author image Julia Michelle
Julia Michelle has been writing professionally since January 2009. Her specialties include massage therapy, computer tech support, land and aquatic personal training, aquatic group fitness and Reiki. She has an Associate in Applied Science from Cincinnati State Technical and Community College in integrative medical massage therapy.
How Does a Blood Pressure Cuff Work?
A doctor measures a patients blood pressure after wrapping the cuff around his arm. Photo Credit AndreyPopov/iStock/Getty Images

About Blood Pressure Cuffs

A blood pressure cuff is a device used to measure the force of the blood in the veins and arteries. At rest, the force of blood flow is constant and, in healthy individuals, ranges between 110/70 and 120/80. The larger number is the systolic number--the force of blood as the heart contracts. The lower number is the diastolic number--the force of blood as the heart relaxes. If the force of the blood is greater than 120/80, this may indicate hypertension. A blood pressure cuff is specially calibrated to register the force of the blood and help medical personnel determine the patient’s health status. The patient can also monitor his own blood pressure with the use of a home monitor. Blood pressure cuffs come in both manual and automatic versions; they function similarly.

Manual Cuffs

Manual blood pressure cuffs are flexible air bladders connected to a bulb pump assembly. The air bladder may have a cloth or vinyl covering and has a sensor connected to a numbered gauge, which displays the blood pressure reading. The outer covering has markings, which indicate exactly how to place the cuff--the sensor needs to sit directly over artery just above the crook of the elbow. Once the cuff is in place, the tester squeezes the bulb to inflate the cuff. The cuff cuts off blood flow to the arm, stopping the pressure so that the sensor can accurately record when the pressure returns. A valve on the end of the pump bulb releases the air from the cuff. The tester slowly releases the air and the cuff loosens, allowing blood flow. The sensor registers the blood flow as circulation returns and the gauge should jump or pulse in time with the blood pulsing in the artery. As the cuff loosens, the pulsing becomes progressively more faint until it stops completely. The number on the gauge where the pulsing starts is the systolic number, and the number where the pulsing stops is the diastolic number. The tester may also listen to the blood flow with a stethoscope to verify the readings on the gauge. Manual cuffs can be difficult for the layperson to use and are most often used by medical professionals.

Automatic Cuffs

Automatic blood pressure cuffs run on either electricity or battery power and have a digital screen that displays the blood pressure reading. Automatic cuffs work on a the same principle as the manual cuffs -- they inflate to cut off blood flow, then slowly release and register the points at which the pulse starts and stops. Once the test is complete, the unit displays both the systolic and diastolic number on the screen. Some automatic cuffs also register pulse rate and have a fail-safe that warns if the cuff is not in place. An automatic cuff is much easier to use but may also provide slightly different readings.

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