Overview of Ankle Brachial Index
The ankle-brachial index (ABI) is a simple method used by doctors to check the health of your blood vessels. It involves looking at the ratio of your blood pressure at your ankle compared to your arm. This helps them understand how well your blood is flowing and if your blood vessels are experiencing any resistance.
The size of your blood vessels is a primary factor in this examination. If the vessels have become narrow, it could be due to stuff building up on the inside of the vessels (like plaque or tears in the lining) or even pressure from outside the vessels (like from surrounding tissues).
Anatomy and Physiology of Ankle Brachial Index
The Ankle-Brachial Index (ABI) is a measurement doctors use to check your blood flow. It involves checking blood flow in three blood vessels: one in your arm (the brachial artery) and two in your feet (the dorsalis pedis and posterior tibial arteries).
The dorsalis pedis artery starts a little above your ankle, around the area between two muscles in your leg, the tibialis anterior and extensor hallucis longus muscles – these can be referred to as EHL for short. This artery generally crosses under the EHL and goes between the EHL and another muscle called the extensor digitorum longus muscle, or EDL. Sometimes it may cross at different points nearer the ankle or further down the foot. A helpful tip in finding this artery (especially if your pulse or heart rate in your foot is weak) is to move your big toe up and down, as this movement indirectly involves the EHL which can guide you to the artery’s location.
The posterior tibial artery is another blood vessel in your foot. It travels behind your inner ankle bone, between two other muscles in your leg: tibialis posterior and flexor digitorum longus.
The brachial artery is a big blood vessel in your upper arm. It can often be felt on the inside of your elbow, next to the tendon of your biceps muscle.
These three blood vessels are very important for doctors when they’re checking your ABI, as any change in blood flow could be a sign of a disease or health condition.
Why do People Need Ankle Brachial Index
The Ankle-brachial Index (ABI), a simple and non-invasive test that measures blood flow to your feet, has many helpful applications. It can be used for spotting health issues early on, confirming a diagnosis, guiding treatment plans, monitoring how well a treatment is working, and predicting future health outcomes. More detailed information about how and why doctors use the ABI is provided in the following sections.
When a Person Should Avoid Ankle Brachial Index
There are few situations where doing an Ankle-Brachial Index (ABI) test, a test to check blood flow in the legs, wouldn’t be recommended:
If a person has a condition known as deep vein thrombosis, which is a blood clot in a deep vein, usually in the leg, it’s recommended to avoid this test. According to the American Heart Association, conducting this test on someone with deep vein thrombosis can cause the blood clot to break apart and move to other parts of the body, which is a serious concern.
If a person has severe pain in the leg, they should also avoid this test. This is because to measure the ABI, a good deal of pressure needs to be applied to the leg. If someone has leg pain, for any reason – whether due to poor blood circulation, fractures, swelling or wounds – this test can cause significant discomfort.
Equipment used for Ankle Brachial Index
The ABI, or ankle-brachial index, can be measured using two main techniques: the manual technique and the automated technique.
The manual technique uses a compression device, known as a blood pressure cuff or sphygmomanometer. It’s important the cuff is the right size – it should be at least 40% of the circumference of your limb. To detect your pulse, your doctor will use a Doppler or stethoscope.
Alternatively, the automated technique uses a device called an oscillometer. If your calf is less than 35 cm in diameter, a regular cuff will be used; diameters over 35 cm will require a larger cuff. It’s worth noting that this method isn’t always perfect: the device can struggle to read low blood pressure and there may be concerns about inaccuracy. This is because the device measures the point of maximum impulse, which correlates more with your mean arterial pressure – the average blood pressure in your arteries during one heartbeat – rather than your actual blood pressure.
Who is needed to perform Ankle Brachial Index?
An ABI, also known as an Ankle-Brachial Index, is a tool used by various health care providers. This includes doctors, nurse practitioners (which are advanced nurses who can perform some tasks usually done by doctors) and other nurses. According to a study, it’s been found that nurses use this tool most frequently in general healthcare settings.
This tool is incredibly useful in many areas of medicine. This includes general medicine, primary care, which is your go-to doctor for regular check-ups, vascular surgery (operations on your veins and arteries), plastic surgery, trauma (emergency situations like accidents), orthopedic surgery (operations on bones and muscles), podiatry (foot and ankle healthcare), emergency medicine, and wound care.
Preparing for Ankle Brachial Index
Here are some steps doctors typically follow to prepare a patient for an Ankle-Brachial Index (ABI) test, which measures how well blood is flowing in the legs:
1. Help the patient rest: Different guidelines suggest that the patient should rest for some time before the test, usually between 10 to 30 minutes. This helps to get more accurate results.
2. Advise against smoking: Research has shown that smoking can affect the blood pressure in your ankle, which could lead to incorrect results.
3. Have the patient lie down: If a patient is sitting during the test, it can increase the ABI value, making the results inaccurate. So, doctors usually have patients lie flat on their back during the test.
4. Provide a quiet space: It’s important to conduct the ABI in a quiet space to avoid any difficulty in hearing the blood flow sounds, which could affect the accuracy of the results.
5. Support the patient’s limbs: To make sure the patient is relaxed and doesn’t move, which could affect the test, doctors ensure the patient’s limbs are well rested and supported.
6. Cover any wounds: If a patient has any wounds, they should be covered to prevent any risk of infection to the wound or the equipment used in the test.
How is Ankle Brachial Index performed
If you’re having an Ankle-Brachial Index (ABI) test, which helps detect if your legs have enough blood flow, here are some things you can expect about where the blood pressure cuff will be placed:
1. Arm: The cuff will be wrapped around the middle of your arm.
2. Ankle: The cuff will be placed just above the bony parts on the sides of your ankle (the malleoli).
The doctor will use a particular device (a stethoscope or Doppler) to listen to your blood flow in your arm and your foot. They will inflate the blood pressure cuff until the sound of your blood flow stops, then slowly release the pressure. The point at which the sound of your blood flow can be heard again is recorded as your ‘systolic’ blood pressure. This is the number that’s usually on top in a blood pressure reading, for example, in a ‘120 over 80’ blood pressure reading, 120 is the systolic pressure.
The doctors tend to follow a specific order when taking these measurements: they will start from one arm, then go to the ankle on the same side, then do the opposite leg, and finally the opposite arm. If the first arm’s measurement differs by 10 or more than the measurement taken from the other arm, they may do a recheck. This is to ensure any nervousness about the test (also known as ‘white coat effect’) didn’t cause an inaccurate high reading the first time around.
The ABI test result is calculated by taking the ratio of the systolic pressure at your ankle compared to your arm. They usually use the highest number recorded from the ankle for this calculation. However, some studies suggest that different methods can also provide helpful information for diagnosis and prognosis. What’s seen as a ‘normal’ value can vary a bit, but the range is typically between 0.87 and 0.95.
Possible Complications of Ankle Brachial Index
Research shows that the results of the same medical test can vary depending on factors like the day it’s done, where it’s done, and the experience level of the healthcare provider. One study demonstrated that the most consistent readings come from tests performed at the higher part of the ankle or arm.
It’s important to keep in mind that a difference of 0.15 or more between test results may be significant. Training for the providers carrying out these tests is also crucial. In fact, it’s been found that only about one out of three providers who perform these procedures do it “correctly” according to the guidelines set in a particular study.
What Else Should I Know About Ankle Brachial Index?
Ankle-brachial index (ABI) is a medical test used to check for peripheral artery disease (PAD), a condition that reduces blood flow to the legs. The test involves comparing the blood pressure in your arm to the blood pressure in your ankle. The results are given as numbers:
– A ‘normal’ result is between 0.9 and 1.4.
– A ‘high’ result is more than 1.4, which can suggest your blood vessels are getting stiff.
– A ‘low’ number, less than 0.9, suggests your blood vessels are narrowing.
– If the test doesn’t give a result, it could mean that the pressure needed to stop blood flow in your vessels is too high.
It’s normal for ABI values to vary a bit depending on factors like your race, gender, age, and height. But the test is generally good at predicting the likelihood of PAD in different groups. Interestingly, for babies, ABI values can be lower than adults, but they reach normal levels after the first year.
The American Heart Association encourages doctors to use this test when checking for PAD in patients who are over 50, smoke, have diabetes, or are older than 70. The test is especially useful for detecting serious PAD cases and is linked to risks of other conditions apart from PAD like kidney disease.
Studies show that having an ABI lower than 0.9 increases risk for conditions like peripheral vascular disease, heart attack, kidney disease, and high blood pressure. Lower ABI values also correlate with a significantly increased risk of stroke and other vascular incidents.
In terms of wound healing, ABI values can give important information. For example, in cases where someone has a critical leg wound, a normal ABI or an ABI that can’t be measured might require more invasive testing. If the ABI shows signs of an abnormal artery state, doctors would usually monitor it closely or recommend procedures to restore blood flow.
In surgery, ABI can help predict healing outcomes. Lower ABI values can lead to increased complications after surgery, such as total knee replacement failure or delayed healing after heart surgery. The test can also be useful in trauma situations to assess for vascular injury.
For those experiencing leg pains–particularly in people over 50–ABI test can sometimes reveal occult or “hidden” PAD. Although the ABI value isn’t always predictive of the current functional status of the leg, lower baseline values do suggest a future decline in leg function.
