How is Blood Pressure Measured?

Blood pressure is measured with two different noninvasive techniques, a manually performed technique known as auscultation and an automated technique known as oscillation.

Manual Technique - Auscultation

The manual technique uses a sphygmometer (if it's handheld, then it's called a sphygmomanometer) to measured the amount of pressure required to occlude blood flow through an artery - usually the brachial artery. The pressure is applied with a band or cuff around the arm (or leg).

As the healthcare provider releases the pressure in the cuff, he or she listens to the artery. As blood begins flowing through the artery, it creates turbulence that can be heard through the stethoscope. When the pressure is low enough, the turbulence stops and the sounds go away. The sounds are called Karotkoff's sounds.

Automated Technique - Oscillation

Automated blood pressure monitoring devices use oscillation in much the same way a healthcare provider uses a stethoscope. The machine detects vibrations (oscillations) as pressure is released and blood flow returns. These are the machines you see in pharmacies and in private homes. If you have a digital blood pressure machine of your own, this is the type of machine you have.

To learn more about blood pressure, read the following:

• What is Blood Pressure?
  Explains what blood pressure is and what the numbers mean.
• What if My Blood Pressure is Too High or Too Low?
  Explains what to do when blood pressure monitors return abnormally high or low readings.

• Top 5 Automated Home Blood Pressure Monitors
  Top picks for automated blood pressure monitors.

References:

Berger, Abi. "Oscillatory Blood Pressure Monitoring Devices." 20 Oct 2001. BMJ.com. 30 Nov 2006

Schettini, C, et al."Ambulatory blood pressure: normality and comparison with other measurements. Hypertension Working Group.." Hypertension. Oct 1999

Staessen, JA, et al."Modern approaches to blood pressure measurement." Occup Environ Med. Aug 2000