In segmental limb pressures, a technique called Doppler ultrasound is used to evaluate blood circulation in the major arteries in the arms or legs. A device called a transducer is passed lightly over different areas of your limbs, directing high-frequency sound waves (ultrasound) at particular arteries. The sound waves are reflected back at frequencies that correspond to the velocity of blood flow, and are converted into audible sounds and graphic recordings.
Duplex scanning combines Doppler ultrasound with real-time ultrasound imaging of the arteries, allowing calculation of the percent of narrowing in the vessels. Images are displayed on a viewing monitor and may also be recorded on film or video for later examination.
Segmental limb pressures are measured by combining Doppler ultrasound with blood pressure measurements at various locations in the arms and legs. By detecting differences in blood pressure at specific locations in different limbs, this test helps to diagnose arterial blockages and other circulation problems. It is most commonly performed in people suspected of having peripheral arterial disease (PAD)—narrowing of arteries in the legs due to the accumulation of plaques (atherosclerosis) that is characterized by leg pain upon exercise.
The ankle-brachial index (ABI), which is determined by recording segmental limb pressures, is the most useful initial test to identify PAD. The ABI is calculated by dividing the systolic blood pressure (that is, the pressure as the heart contracts) in the ankle by the systolic pressure in the brachial artery in the arm. Normally, the ankle pressure should be slightly higher, resulting in an ABI of 1.0 or greater. PAD is indicated if the ABI is less than 1.0; the lower the ABI, the more severe the disease. ABI measurements are usually taken at rest and after a designated amount of exercise on a treadmill. The test is painless.
Purpose of the Segmental Limb Pressures
- To evaluate arterial blood flow in the arms or legs and detect blockages, trauma, or other circulation problems
- To aid in the diagnosis of PAD, determine the location and extent of any arterial blockages, and (with the treadmill test) determine the severity of functional impairment due to PAD
- To monitor the progression of known PAD and evaluate the effectiveness of treatments such as arterial bypass grafts in the legs
- To detect and evaluate possible arterial trauma
Who Performs It
- A nurse or a technician who is trained in ultrasound.
- Blood pressure readings in the thigh may not be possible in obese patients, since a standard cuff may not be large enough to fit.
- Individuals who have extremely rigid (or calcified) arteries may show falsely elevated ankle pressures. This is most common in people with diabetes, but may also be found in people on long-term corticosteroid therapy, kidney dialysis patients, and kidney transplant recipients. To obtain more accurate results, the ABI should be calculated using pressures from the foot or toes instead of the ankle in these patients.
- Arterial plethysmography is sometimes performed concurrently with this test.
Before the Segmental Limb Pressures
- Avoid cigarette smoking for at least 30 minutes before the test, since smoking constricts the peripheral arteries and can interfere with the accuracy of the results.
- You will be asked to remove any clothes covering your legs and arms. You may wear shorts and a short-sleeved shirt or a hospital gown during the test.
- You may be asked to rest for about 20 minutes prior to the test.
What You Experience
- You will lie down on a table or bed.
- A small amount of water-soluble gel is applied to the skin on the areas being examined to enhance sound wave transmission.
- The examiner movers the transducer back and forth over the selected limbs to obtain different views of the artery or arteries being examined.
- Once clear images are obtained, they are recorded on film or video for later analysis.
- The test usually takes 20 to 30 minutes.
Segmental limb pressures with ABI index:
- You will lie on either a bed or table with your arms at your sides.
- Blood pressure cuffs are wrapped above the elbow on both arms. The cuffs are inflated, and blood pressure is measured in the brachial artery on both sides. (The higher of the 2 pressures is used to calculate your ABI.)
- To examine segmental pressures in the legs, cuffs are then placed at various points—typically, at the thigh, calf, ankle, foot, and toe level. If the arms are being tested, cuffs are placed on the upper arms, forearm, and sometimes the hand or fingers.
- A small amount of water-soluble gel is applied to various areas of skin on the limb being examined to enhance sound wave transmission.
- Each cuff is inflated in turn and blood pressures are measured at each site on the limb. This is done with the aid of an ultrasound transducer that is held against the skin.
- This procedure is repeated in the other leg or arm.
- To determine your exercise ABI, you will be asked to walk on a treadmill for a few minutes (your doctor will specify the treadmill setting and time period). Your ankle pressure is measured before and after the exercise.
- The test usually takes 30 to 45 minutes.
Risks and Complications
- Ultrasound is painless, noninvasive, and involves no exposure to radiation. There are no associated risks.
After the Segmental Limb Pressures
- The examiner removes the conductive gel from your skin.
- You are free to leave the testing facility and resume your normal activities.
- A physician reviews the ultrasound images, ABI and exercise ABI, and other test data for evidence of any abnormality. If an arterial blockage is indicated, comparing blood pressures at various locations in the leg can help to determine where it is located.
- In some cases, additional tests, such as arteriography or magnetic resonance angiography, are required to further evaluate abnormal findings and determine an appropriate course of treatment.
- If no further tests are warranted, your doctor will recommend an appropriate schedule of follow-up exams and/or treatment.
The Johns Hopkins Consumer Guide to Medical Tests
Simeon Margolis, M.D., Ph.D., Medical Editor
Updated by Remedy Health Media