Ankle brachial pressure index
Encyclopedia
The Ankle Brachial Pressure Index (ABPI), known more commonly as an ABI, is the ratio of the blood pressure
in the lower legs to the blood pressure in the arms. Compared to the arm, lower blood pressure in the leg is an indication
of blocked arteries (peripheral vascular disease). The ABI is calculated by dividing the systolic
blood pressure
at the ankle by the systolic blood pressures in the arm.
(blood pressure cuff) are usually needed. The blood pressure cuff is inflated proximal to the artery in question. Measured by the Doppler wand, the inflation continues until the pulse in the artery ceases. The blood pressure cuff is then slowly deflated. When the artery's pulse is re-detected through the Doppler probe the pressure in the cuff at that moment indicates the systolic pressure of that artery.
The higher systolic reading of the left and right arm brachial artery
is generally used in the assessment. The pressures in each foot's posterior tibial artery
and dorsalis pedis artery
are measured with the higher of the two values used as the ABI for that leg.
The ABPI test is a popular tool for the non-invasive assessment of PVD. Studies have shown the sensitivity
of ABPI is 90% with a corresponding 98% specificity
for detecting hemodynamically
significant (Serious) stenosis
>50% in major leg arteries, defined by angiogram.
However, ABPI has known issues:
These issues have rendered ABI unpopular in primary care, due to the perceived difficulties and time taken.
However, technology is emerging that allows for the oscillometric calculation of ABI. This is achieved by doing simultaneous readings of blood pressure at the levels of the ankle and upper arm using specially calibrated oscillometric modules. Several Manufacturers have devices on the market. The main interest in the introduction of an oscillometric system to measure ABI is that it standardizes the method and makes the measurement of ABI accessible to all doctors.
).
However, an ABPI value greater than 1.3 is considered abnormal, and suggests calcification
of the walls of the arteries and incompressible vessels, reflecting severe peripheral vascular disease.
Provided that there are no other significant conditions affecting the arteries of the leg, the following ABPI ratios can be used to predict the severity of PAD as well as assess the nature and best management of various types of leg ulcers:
.
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
in the lower legs to the blood pressure in the arms. Compared to the arm, lower blood pressure in the leg is an indication
Indication
Indication can refer to:* A synonym for Sign.* Human interface Highlighting the single object pointed to as a cursor is moved, without any other user action such as clicking, is indication....
of blocked arteries (peripheral vascular disease). The ABI is calculated by dividing the systolic
Systole (medicine)
Systole is the contraction of the heart. Used alone, it usually means the contraction of the left ventricle.In all mammals, the heart has 4 chambers. The left and right ventricles pump together. The atria and ventricles pump in sequence...
blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
at the ankle by the systolic blood pressures in the arm.
Method
A Doppler ultrasound blood flow detector, commonly called Doppler Wand or Doppler probe, and a sphygmomanometerSphygmomanometer
A sphygmomanometer or blood pressure meter is a device used to measure blood pressure, comprising an inflatable cuff to restrict blood flow, and a mercury or mechanical manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just...
(blood pressure cuff) are usually needed. The blood pressure cuff is inflated proximal to the artery in question. Measured by the Doppler wand, the inflation continues until the pulse in the artery ceases. The blood pressure cuff is then slowly deflated. When the artery's pulse is re-detected through the Doppler probe the pressure in the cuff at that moment indicates the systolic pressure of that artery.
The higher systolic reading of the left and right arm brachial artery
Brachial artery
The brachial artery is the major blood vessel of the arm.It is the continuation of the axillary artery beyond the lower margin of teres major muscle. It continues down the ventral surface of the arm until it reaches the cubital fossa at the elbow. It then divides into the radial and ulnar arteries...
is generally used in the assessment. The pressures in each foot's posterior tibial artery
Posterior tibial artery
The posterior tibial artery of the lower limb carries blood to the posterior compartment of the leg and plantar surface of the foot, from the popliteal artery...
and dorsalis pedis artery
Dorsalis pedis artery
In human anatomy, the dorsalis pedis artery , is a blood vessel of the lower limb that carries oxygenated blood from the dorsal surface of the foot. It arises at the anterior aspect of the ankle joint and is a continuation of the anterior tibial artery...
are measured with the higher of the two values used as the ABI for that leg.
-
- Where PLeg is the systolic blood pressure of dorsalis pedis or posterior tibial arteries
- and PArm is the highest of the left and right arm brachial systolic blood pressure
The ABPI test is a popular tool for the non-invasive assessment of PVD. Studies have shown the sensitivity
Sensitivity and specificity
Sensitivity and specificity are statistical measures of the performance of a binary classification test, also known in statistics as classification function. Sensitivity measures the proportion of actual positives which are correctly identified as such Sensitivity and specificity are statistical...
of ABPI is 90% with a corresponding 98% specificity
Sensitivity and specificity
Sensitivity and specificity are statistical measures of the performance of a binary classification test, also known in statistics as classification function. Sensitivity measures the proportion of actual positives which are correctly identified as such Sensitivity and specificity are statistical...
for detecting hemodynamically
Hemodynamics
Hemodynamics, meaning literally "blood movement" is the study of blood flow or the circulation.All animal cells require oxygen for the conversion of carbohydrates, fats and proteins into carbon dioxide , water and energy in a process known as aerobic respiration...
significant (Serious) stenosis
Stenosis
A stenosis is an abnormal narrowing in a blood vessel or other tubular organ or structure.It is also sometimes called a stricture ....
>50% in major leg arteries, defined by angiogram.
However, ABPI has known issues:
- ABPI is known to be unreliable on patients with arterial calcificationCalcificationCalcification is the process in which calcium salts build up in soft tissue, causing it to harden. Calcifications may be classified on whether there is mineral balance or not, and the location of the calcification.-Causes:...
(hardening of the arteries) which results in less or incompressible arteries, as the stiff arteries produce falsely elevated ankle pressure, giving false negatives). This is often found in patients with diabetes melitus (41% of PAD patients have diabetes), renal failureRenal failureRenal failure or kidney failure describes a medical condition in which the kidneys fail to adequately filter toxins and waste products from the blood...
or heavy smokerTobacco smokingTobacco smoking is the practice where tobacco is burned and the resulting smoke is inhaled. The practice may have begun as early as 5000–3000 BCE. Tobacco was introduced to Eurasia in the late 16th century where it followed common trade routes...
s. ABPI values < 0.9 & >1.3 should be investigated further regardless. - Performing ABPI is time consuming.
- Resting ABPI is insensitive to mild PAD. Treadmill tests (6 minute) are sometimes used to increase ABPI sensitivity, but this is unsuitable for patients who are obese or have co-morbidities such as Aortic aneurysmAortic aneurysmAn aortic aneurysm is a general term for any swelling of the aorta to greater than 1.5 times normal, usually representing an underlying weakness in the wall of the aorta at that location...
, and increases assessment duration. - Lack of protocol standardisation, which reduces intra-observer reliability.
- Skilled operators are required for consistent, accurateACCURATEACCURATE was established in 2005 by a group of computer scientists, psychologists and policy experts to address problems with electronic voting...
results.
These issues have rendered ABI unpopular in primary care, due to the perceived difficulties and time taken.
However, technology is emerging that allows for the oscillometric calculation of ABI. This is achieved by doing simultaneous readings of blood pressure at the levels of the ankle and upper arm using specially calibrated oscillometric modules. Several Manufacturers have devices on the market. The main interest in the introduction of an oscillometric system to measure ABI is that it standardizes the method and makes the measurement of ABI accessible to all doctors.
Interpretation of results
In a normal subject the pressure at the ankle is slightly higher than at the elbow (there is reflection of the pulse pressure from the vascular bed of the feet, whereas at the elbow the artery continues on some distance to the wrist). The ABPI is the ratio of the highest ankle to brachial artery pressure and an ABPI of greater than 0.9 is considered normal (Free from significant PADPeripheral artery occlusive disease
Peripheral vascular disease , commonly referred to as peripheral arterial disease or peripheral artery occlusive disease , refers to the obstruction of large arteries not within the coronary, aortic arch vasculature, or brain. PVD can result from atherosclerosis, inflammatory processes leading to...
).
However, an ABPI value greater than 1.3 is considered abnormal, and suggests calcification
Calcification
Calcification is the process in which calcium salts build up in soft tissue, causing it to harden. Calcifications may be classified on whether there is mineral balance or not, and the location of the calcification.-Causes:...
of the walls of the arteries and incompressible vessels, reflecting severe peripheral vascular disease.
Provided that there are no other significant conditions affecting the arteries of the leg, the following ABPI ratios can be used to predict the severity of PAD as well as assess the nature and best management of various types of leg ulcers:
| ABPI value | Interpretation | Action |
|---|---|---|
| 1.0 - 1.40 | Normal range | None |
| 0.91 - 0.99 | Borderline | Modify risk factors |
| ≤ 0.90 | Arterial disease | Smoking cessation Antiplatelet and antithrombotic therapy(e.g. aspirin 75-325 mg daily or clopidogrel 75 mg daily) |
Predictor of atherosclerosis mortality
Studies in 2006 suggests that an abnormal ABPI may be an independent predictor of mortality, as it reflects the burden of atherosclerosisAtherosclerosis
Atherosclerosis is a condition in which an artery wall thickens as a result of the accumulation of fatty materials such as cholesterol...
.
See also
- Peripheral vascular disease
- Peripheral vascular examinationPeripheral vascular examinationIn medicine, the peripheral vascular examination is a series of maneuvers to elicit signs of peripheral vascular pathology. It is performed as part of a physical examination, or when a patient presents with leg pain suggestive of a cardiovascular pathology....
- Intermittent claudicationIntermittent claudicationIntermittent claudication is a clinical diagnosis given for muscle pain , classically in the calf muscle, which occurs during exercise, such as walking, and is relieved by a short period of rest.Claudication derives from the Latin verb claudicare, "to limp".-Signs:One of the hallmarks of arterial...