Patient Basics: Arterial Blood Flow Studies of the Legs (Segmental Doppler Pressures)

Originally published by Harvard Health.

What is the test?

People who have leg pain when exercising may need an evaluation to make sure they have normal blood flow through their leg arteries. Normally blood pressure is similar whether it is measured in the legs or in the arms. If blood pressure is lower in the legs, it usually means that cholesterol buildup inside the leg arteries is interfering with circulation. By taking accurate blood pressure measurements at different locations along your legs, your doctors can determine if you have any arterial narrowing and, if so, where.

In order to get accurate blood pressure measurements, your doctor uses a technique called Doppler ultrasound. Doppler ultrasound is a painless way to detect blood flowing through a small artery. It uses sound waves and a type of sonar detection system to make noise when blood flow is detected. For arterial studies of the legs (called segmental Doppler pressures), Doppler ultrasound is used in place of the stethoscope that doctors usually use when taking blood pressures.

How do I prepare for the test?

You may want to wear shorts for this exam, and your feet should be bare during the test. If you are not wearing shorts, you may have to change into a hospital gown.

What happens when the test is performed?

You lie on a table and a technician or doctor wraps blood pressure cuffs around one of your legs in four or five locations (including the thigh, calf, and ankle). He or she then squirts some clear jelly onto your skin to help the Doppler sensor (which resembles a wand or pen) slide around easily and to help conduct sound waves through your skin.

Each blood pressure cuff is inflated two times. The first time, the cuff is only inflated part way so that it exerts a gentle pressure on your leg. The cuff sends information to a computer about the size of your leg and how elastic your arteries seem to be as the pressure is increased. A wavy line that signifies your blood flow appears on a video screen.

The second time, each cuff is inflated to exert more pressure on your leg. This temporarily cuts off circulation in the leg. Many patients briefly experience some cramping pain in the calf or thigh (similar to the sensation you experience when a blood pressure cuff is inflated around your arm). As the cuff is deflated, the doctor places a Doppler sensor against your foot to detect the moment when blood flow starts up again. (When it does, you will hear a noise that sounds like your heartbeat.) Checking the air pressure of the deflating cuff at this time shows the leg blood pressure.

After all the cuffs on one side have been tested, the other leg is checked in the same way. For comparison, you also have your blood pressure checked in each arm using the Doppler Technique. The whole test usually takes 45 minutes.

Some patients have their leg pressures checked both before and after exercise. If this is the case for your test, you are asked to walk on a treadmill for a short time and then have the test again afterward. The exercise version of this test takes more time.

What risks are there from the test?

There are no risks.

Must I do anything special after the test is over?

The jelly will be wiped off. You will have no side effects from the test.

How long is it before the result of the test is known?

Your doctor should receive a formal report within a few days.