What is the test?
People who have leg pain when exercising may need an evaluation to make sure that they have normal blood flow through their leg arteries. The blood pressure measured in the legs should be, in a normal person, very similar to the blood pressure that can be measured in the arms. Lower blood pressures in the legs usually means that cholesterol buildup inside the leg arteries has reached the point where it is interfering with circulation. By taking accurate blood pressure measurements for the arteries at different locations along your legs, your doctors can see if you have narrowing of your arteries and can understand how high or low in your leg a cholesterol blockage might be.
In order to get accurate blood pressure measurements, your doctor will use 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 will be 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 you will need to have bare feet during the test. If you are not wearing shorts, you will probably be asked to change into a hospital gown.
What happens when the test is performed?
You will lie on a table and (depending on your size) a technician or doctor will wrap blood pressure cuffs around one of your legs in four or five locations. He or she will squirt some clear jelly onto the top of your foot to help the Doppler sensor slide around easily and to help conduct sound waves through your skin. The sensor, resembling a wand or a pen, will be placed against your skin in this jelly.
Each blood pressure cuff will be inflated two times. The first time the cuff is inflated, it will only be inflated part way (to a gentle pressure) and it will send a signal to a machine next to you 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 will appear on a screen.
The second time each cuff is inflated, it will be inflated to a higher pressure. Just as happens when you have blood pressure measurements taken in your arm, the inflated blood-pressure cuff will temporarily cut off circulation in the leg. For many patients, this briefly causes some cramping pain in the calf or thigh. As the cuff is deflated, the Doppler sensor on the foot detects the moment when blood flow starts up again by making 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 will be checked in the same way. For comparison, you will also have a blood pressure checked in each arm using the Doppler technique. The whole test usually requires close to 45 minutes.
Some patients have their leg pressures checked both before and after exercise. If this is the case for your test, you will be asked to walk on a treadmill for a short time and then will have the test repeated afterward. The exercise version of this test requires more time to complete.
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 results are usually written up into a formal report for your doctor to review. Your doctor should receive the report within a few days.