Ankle-Brachial-Index (ABI)

The ABI describes the ratio of the systolic blood pressure measured on the ankle in relation to the value measured on the upper arm. The pressure is measured on both upper arms and the higher value is taken to calculate the ABI. It is the relationship between central and peripheral blood pressures which is, therefore, a very good parameter to diagnose peripheral arterial occlusive diseases.

The measurement of peripheral systolic blood pressures at different locations can be made in various ways. Often the values ​​were determined using a pressure cuff with a manometer and a vascular Doppler to detect the arterial pulsation. At the beginning the cuff is inflated until the arterial blood flow in the vessel is interrupted. Afterwards the cuff is deflated slowly and the Doppler probe is placed on a selected vessel to detect the beginning of the arterial pulsation. The systolic blood pressure is taken from the manometer when the first pulsation has been identified. This procedure has to be repeated for each vessel. For the calculation of the ABI the highest pressure value out of all vessels is taken.

Such a procedure is time consuming and requires an experienced operator. Additionally, the measurements can be made only consecutively whereby during the course of examination the central blood pressure can change so that the calculated ABI value could be inaccurate. Moreover, repeated interruptions of the arterial blood flow can result in vascular reactions (vasodilatation) which can influence the measured value of the blood pressure.

Because of the mentioned limitations nowadays, cuffs are placed on the upper arms and ankles and the blood pressures are measured simultaneously on all locations using the oscillometric method what allows to get operator independent and accurate results in a very short time. But it is not possible to evaluate the vessels of the ankle separately.

This new approach enables to determine also peripheral pulse wave propagation times and, especially, the differences between both sides whereby a considerable difference is an indicator for the existence of a potential arterial occlusion. Additionally, the shape of the pulse waves can be analysed whereby more round pulse waves suggest arteriosclerotic changes of the vessels. Both additional parameters increase the diagnostic value of ABI.

In summary the oscillometric determination of ABI is more simple, less time consuming and provides additional diagnostic information for the evaluation of peripheral vessels without additional efforts.