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Vascular studies may be recommended by your doctor to aid in the diagnosis of peripheral vascular disease or other vascular diseases or conditions such as blood clots. These types of tests include the ankle-brachial index test and the arterial Doppler ultrasound.
The ankle-brachial index test is done by measuring blood pressure at the ankle and in the arm while a person is at rest. Measurements are then repeated at both sites after 5 minutes of walking on a treadmill. By dividing the highest blood pressure at the ankle by the highest recorded pressure in either arm, the ankle-brachial index (ABI) can be calculated. The ABI result is used to predict the severity of peripheral vascular disease of the legs that may be present. A decrease in the ABI result with exercise is a sensitive indicator that significant peripheral vascular disease is probably present. A normal resting ankle-brachial index is 1 or 1.1. This means that your blood pressure at your ankle is the same or greater than the pressure at your arm and there is no significant narrowing or blockage of blood flow. The resting ankle-brachial index is abnormal when the ABI is less than 0.95. This may indicate significant narrowing of one or more blood vessels in the legs.
An arterial Doppler ultrasound test uses reflected sound waves to evaluate blood as it flows through a blood vessel. It helps doctors evaluate blood flow through the major arteries and veins of the arms, legs, and neck. It can show blocked or reduced blood flow in the arteries of the neck that could cause a stroke. It can also reveal blood clots in leg veins that could break loose and block blood flow to the lungs (pulmonary embolism).
During duplex Doppler ultrasound, a handheld instrument called a transducer is passed lightly over the skin above a blood vessel. The transducer sends and receives sound waves that are amplified through a microphone. The sound waves bounce off solid objects, including blood cells. The movement of blood cells causes a change in pitch of the reflected sound waves (called the Doppler effect). If there is no blood flow, the pitch does not change. Information from the reflected sound waves can be processed by a computer to provide graphs or pictures that represent the flow of blood through the blood vessels. Doppler ultrasound is done to:
- Help detect blood clots and blocked or narrowed blood vessels in almost any part of the body, especially in the neck, arms, and legs. Blocked or narrowed arteries of the neck can cause dizziness, loss of vision, paralysis, weakness, or numbness. Blood clots in deep veins of the leg can cause leg pain and swelling and can increase a person's risk of pulmonary embolism.
- Evaluate leg pain that may be caused by intermittent claudication, a condition caused by atherosclerosis of the lower extremities.
- Evaluate blood flow after a stroke or other condition that might be caused by a problem with blood flow. Evaluation of a stroke can be done through a technique called transcranial Doppler ultrasound.
- Map veins that may be used for blood vessel grafts. It can also evaluate the condition of grafts used to bypass blockage in an arm or leg.
- Determine the amount of blood flow to a transplanted kidney or liver.
- Monitor the flow of blood following blood vessel surgery.
- Determine the presence, amount, and location of arterial plaque. Plaque in the carotid arteries can reduce blood flow to the brain and may increase the risk of stroke.
Nicotine causes blood vessels to constrict; therefore, you may be asked to avoid products that contain nicotine (cigarettes, chewing tobacco) for 30 minutes to 2 hours before the test. You will need to remove any jewelry that might interfere with the Doppler ultrasound scan. You will need to take off all or most of your clothes, depending on which area is being examined. You will be given a cloth or paper covering to use during the test. For abdominal scans, you will lie on your back. For chest scans, you will lie on your back with your neck slightly extended. For head and neck scans, your head may be turned to one side. For an arm or leg scan, your head is slightly raised and the exposed arm or leg is turned slightly outward. Gel is applied to the skin to promote the passage of the sound waves. The transducer is placed in the gel and moved along the skin. You need to lie very still during the procedure. You may hear sounds that represent the flow of blood through the blood vessels.
There is normally no discomfort involved with having a Doppler ultrasound test. The gel may feel cold when it is applied to your skin unless it is first warmed to body temperature. If your blood pressure is taken during the test, you will feel pressure when the blood pressure cuffs are inflated. There are no known risks associated with a Doppler ultrasound test.