Ankle Blood Pressure Measurement

Measurement of ankle pressures is a very important and yet simple examination method in vascular medicine.

Principle

The examination consists of measuring the blood pressure of the upper and lower extremities using a pressure cuff and subsequently comparing them. When measuring the blood pressure in the lower extremities, we rather use a device called pencil Doppler probe instead of the classic stethoscope. The probe really looks like a pencil and it transmits ultrasound signal. When we touch the skin above a local artery, the device finds the blood flow and emits a audible sound.

 

We put the pressure cuff above the artery found by the pencil Doppler and inflate the cuff until we hear no sound signal from the probe. After that, we slowly deflate the cuff and write down the pressure, when the sound (i.e. blood flow in the artery) occurs.

 

The value of the ankle pressure is compared to the blood pressure detected in the upper limb. There is a value known as ankle brachial index (ABI), which is the ratio of the ankle pressure to the arm pressure. In healthy leg, the blood pressure should be similar (or slightly higher) to the arm pressure and the ABI should be bigger than 1. When the ABI is much lower than 1, it means that the ankle pressure is abnormally low and this is typical for impaired blood flow to the leg in peripheral artery disease.

 

Ankle pressure

 

Scheme - Measurement of ankle blood pressure

 

Preparation

The examination does not require any special preparation. It is possible to eat and drink normally.

Indications

The examination is important in the diagnosis of peripheral artery disease (PAD), which is caused by atherosclerosis of lower limbs' arteries. Clinical symptoms include leg pain during physical exercise, which disappears at rest and arterial leg ulcers in later stages. When the ankle pressure and ankle brachial index show possible PAD, the doctor may indicate more invasive examination such as the angiography.

Disadvantages

The test may be inaccurate in patients who have rigid and incompressible wall of arteries due to their excessive calcification (typically patients with diabetes). In such patients, the values of ankle pressures may be falsely higher than they actually are.

Advantages

The main advantage is the simplicity, non-invasiveness and availability of the examination. The procedure is painless and the patient does not have to be exposed to radiation. The results are valuable for suspicion of PAD and its clinical severity.