Testing Methods for Endothelial Function and Arterial Tone

Several non-invasive procedures are available to test endothelial function and arterial tone, all based on evaluating the response to reactive hyperemia.

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    Over a defined period, typically five minutes, the arterial blood supply to the forearm is interrupted by occluding the brachial artery with an inflated cuff, placed on the upper arm or forearm [5]. After deflation of the cuff, blood rushes into the forearm producing an overshoot in perfusion (reactive hyperemia). The increased blood flow will lead to an increase in friction at the arterial wall, determined by ‘shear stress’, primarily stimulating NO release by the endothelial layer, with additional more intricate mechanisms being involved. NO production in turn leads to a lower tension of the smooth muscle and a widening of the brachial artery diameter. This phenomenon, called Flow Mediated Dilation or FMD, is directly evaluated using procedures described in more detail below.
    Other modalities assess changes in the vascular bed perfusion secondary to the brachial occlusion.

Today, several modalities are available for determining, evaluating, and monitoring endothelial function:

Flow Mediated Dilation or FMD is considered the Gold Standard in this field. However, the procedure is clinically challenging, requiring a high level of technical and human resource and skill. In the below article we discuss and propose how the FMD testing procedure and more so its evaluation can be facilitated.

Flow Mediated Slowing or FMS works according to the same basic principles as FMD, but can be carried out at a substantially lower entry level of cost and expertise, working mostly operator-independent.

While FMD and FMS address endothelial function of predominantly bigger vasculature, function tests of smaller vessels and the vascular bed are also available which may be advantageous in a normal population, e.g. in epidemiological studies and phenotyping.