Ankle-Brachial-Index (ABI)


ABI is the newest and most reliable method of determining the highest arterial occlusive and opening pressures at all four limbs. This patented system uses a combination of pressure measurement and plethysmography. This method produces the most accurate and professional expression of the Ankle-Brachial-Index (ABI).

ABI is the gold standard for screening and diagnosing PAOD. Below is the range and interpretation of readings:

• Normal: 1 to 1.29.
• Borderline: 0.91 to 0.99
• Mild PAOD: 0.71 to 0.90
• Medium severe PAOD: 0.41 to 0.7
• Severe PAOD: <0.4

Diabetics present an exception to these typical readings. Since arterial compressibility is a result of mediasclerosis, arterial pressure in diabetics is very high. Therefore, an ABI reading of 1.3 or greater could give rise to a mediasclerosis diagnosis. The same may be true for patients with chronic kidney deficiency as they also suffer from mediasclerosis.

Overview


The ankle-brachial index (ABI) collects blood pressures from your ankle and arm then compares the two values to determine how well blood is flowing in your body. This value can be used to diagnose Peripheral Arterial Disease (P.A.D). The ABI value will give insight into how P.A.D. may be affecting your limbs, however, it doesn’t indicate where blockages occur or the extent to which blockage has taken place.

A buildup of plaque causes arteries to narrow and harden. This condition is called atherosclerosis. When arteries in a patient’s legs become occluded, this condition is referred to as Peripheral Arterial Disease (P.A.D). Blood flow to the legs is compromised due to these clogged and hardened arteries. While P.A.D. appears most frequently in the legs, it may also affect arteries leading to the arms, stomach, brain, kidneys and aorta. When hardening occurs in arteries inside the heart, the condition is called coronary artery disease or cardiovascular disease.

Testing for ABI is generated by collecting blood pressures at the ankle and arm while a patient is at rest. The patient is then instructed to walk on the treadmill for 5 minutes. After this exercise, measurements from the ankle and arm are collected again.

The ABI is calculated by dividing the highest ankle blood pressure reading by the highest arm reading. The resultant data can be used to determine the degree of PAD present. For instance, a drop in the ABI reading after exercise indicates a significant level of PAD.

Why Perform the Test:
ABI assists in screening for peripheral arterial disease present in the legs.

Results:
The ABI reading assists in diagnosing peripheral arterial disease (PAD). A drop in ABI after exercise indicates a significant level of PAD may be present.

Normal
1 or 1.1 is a normal resting ankle-brachial index. This value indicates no significant blockages or lowered blood flow.

Abnormal
Less than 1 indicates an abnormal resting ankle-brachial index. Specific readings indicate the following:
Less than 0.95: Significant narrowing of one or more blood vessels in the legs.
Less than 0.8: Pain in the foot, leg, or buttock may occur during exercise (i.e. intermittent claudication).
Less than 0.4: Rest pain may occur.
Less than 0.25: Severe limb-threatening PAD is likely present.

Important Considerations

Leg pain may be a factor during the treadmill testing if peripheral arterial disease (PAD) is present. Arterial disease that has not been diagnosed may produce inaccuracies in the test results.

Inaccuracies may also occur if the blood vessel being measured is significantly calcified. This may be the case if the patient is diabetic or suffers from a kidney condition (i.e. renal insufficiency). Highly abnormal ABI results suggest subsequent testing in order to locate the site and severity of PAD.

Toe Brachial Index (TBI)


Purpose
The reading is derived in order to determine the severity of peripheral arterial disease present in a lower extremity.

The test is performed using a small blood pressure cuff that is fitted around a toe along with a photoplethysmograph (PPG) infrared light sensor. The resultant toe brachial index (TBI) is generated using the systolic blood pressure readings from the arm and toe.

How is the exam performed?
Blood pressure cuffs are fitted around the patient’s arm and big toe and they are asked to assume a reclined position. Once laid back, the patient’s cuffs will be inflated above the normal systolic blood pressure then deflated. Measurements are taken from both the arm and toe using the Doppler instrument (PPG). The toe systolic pressure is then divided by the highest arm pressure to generate a TBI reading for each leg.

0.75 TBI is considered normal.

What is Peripheral Arterial Disease (PVD)
Over time, arteries may become hardened due to both lifestyle and genetic reasons. This arterial hardening is referred to as atherosclerosis. The condition produces poor circulation and worsens over time but may not become apparent to the sufferer until later in life. Obvious symptoms may not be detectable until the artery has narrowed by 60% or more. The reason patients may become symptomatic earlier correlates to the body’s adaptation to arterial narrowing. In response to arterial occlusion, smaller peripheral arteries are developed to permit blood flow around the blockages. This process is referred to as collateral circulation. Should a blood clot or piece of cholesterol or calcium break off and move into the artery, a blockage will occur and blood flow may be entirely disrupted. The area most commonly damaged by PAD are the legs.

What happen if the disease worsens?
The degree of PAD is dependent on other when it is diagnosed and other lifestyle risk factors such as smoking, high cholesterol, heart disease and diabetes. Left to worsen, PAD could produce circulation issues that cause pain in the legs and feet even while at rest. This condition is known s rest pain and typically becomes more severe at night. Lowering the legs to allow gravity to draw blood downwards tends to help relieve the pain.

Critical Limb Ischemia
As PAD progresses and circulation deteriorates, PAD may lead to Critical Limb Ischemia (CLI). In this stage, blockages have become so severe that legs and feet are no longer receiving blood flow vital for growth and repair. Persistnent sores, gangrene and even amputation may result from this advanced condition.

What are the first signs of Peripheral Arterial Disease?
Initial symptoms of PAD include intermittent claudication or painful cramping in the legs while walking. Rest causes the pain to desist. The pain may be so severe that normal walking is affected. In some cases, patients experience a numb, weak or heavy feeling in the muscles as opposed to pain.

What are some other symptoms?
Patients with more advanced symptoms of PAD will experience a burning or aching sensation in the feet or toes while resting, particularly at night while laying in bed. In addition, other symptoms include the following:

• Cool sensation in the feet or legs
• Colour changes in the skin and loss of hair
• Persistent sores in the feet and toes that don’t heal

Silent PAD
Because PAD can advance relatively unnoticed, many people affected with the condition are unaware and do not seek treatment. Undiagnosed individuals are at a higher risk for early heart attack or stroke. In fact, individuals with PAD are six times more likely to die from heart disease than those without the condition. It follows that screening for PAD is vital to cardiovascular health.

Risk factors

Individuals at risk for developing PAD exhibit one or more of the following risk factors:

Smoking
Cigarette smoking is the primary risk factor for PAD. The act of smoking not only promotes the development of arterial disease but continued smoking hinders treatment.

Diabetes
Diabetics tend to have narrowed arteries dues to calcification so this puts them at risk for developing PAD.

Age
Individuals 50 years or older are at a greater risk of developing PAD. While it affects both men and women, PAD does occur slightly more often in men.

History of Heart Disease
Patients with a family history of cardiovascular disease are more likely to develop PAD.

Hypertension (high blood pressure)
Persistent high blood pressure damages the arterial walls thereby putting patients at a higher risk for developing PAD.

High levels of Homocysteine
Some studies show a correlation between this amino acid found in blood and high risk of developing PAD.