Arterial Occlusion Plethysmography (AOP)
This method is a non-invasive function test to evaluate the arterial system particularly in the legs.
For the examination the patient is lying and the legs are in a lifted position over heart level so that the venous blood can flow out. It isn´t necessary to empty the veins completely. Cuffs are placed on the upper legs. During the course of examination the arterial inflow is measured several times consecutively to evaluate its course.
In general, to measure the arterial inflow the cuffs are inflated until a diastolic pressure of about 80 mmHg so that the arterial blood can flow in but the venous blood cannot flow out. The filling curve of the veins is recorded whereby its initial slope characterises the arterial inflow. After a few seconds the cuffs are deflated and the measuring cycle is completed.
At the beginning of the course of examination the described procedure is repeated 3 times to define the averaged arterial inflow at rest. Afterwards the cuffs are inflated until a suprasystolic pressure to provoke a total interruption of the arterial blood flow in the legs for 3-5 minutes to induce a hyperemia what can be considered as a standardized exercise test. Then the cuffs are deflated completely and the arterial inflow is measured 5-7 times consecutively as described above. The course of the arterial inflow over time allows to evaluate the severity of arterial obliterative processes and the haemodynamic quality of collateral circulation. The higher and the earlier the peak of the arterial inflow the better the arterial system.
During this course of examination in the lower legs blood volume changes take place which can be measured by Impedance Plethysmography (IPG) or strain gauges.
|AI||Arterial Inflow||Maximum velocity of blood volume change (filling) after venous occlusion|