**6. Flow mediated dilation**

Endothelial function is linked to cardiovascular risk factors and provides prognostic informa‐ tion for cardiovascular diseases [61]. Endothelial dysfunction is regarded as the initial step of atherosclerosis and therefore as the earliest detectable manifestation of vascular end-organ damage. It can be assessed using several methods, with flow-mediated dilation (FMD) being currently the gold-standard in non-invasive evaluation of endothelial dysfunction. In this ultrasound-based method brachial artery diameter is measured before and after an increase in shear stress that is induced by reactive hyperemia. When a sphygmomanometer cuff placed on the forearm or upper-arm and is inflated at 50 mm/Hg above systolic pressure, arterial inflow is occluded causing a local ischemia and dilation of downstream arteries. Cuff deflation induces a high-flow state through the brachial artery (reactive hyperemia) to accommodate the dilated resistance vessels. The increased shear stress leads to endothelium dependent dilation of the brachial artery. FMD occurs predominantly as a result of local endothelial release of nitric oxide. Figure 1 shows the B-mode and Doppler flow images of the brachial artery of a patient with hypertension at baseline and after deflation of the cuff (hyperemia). The FMD was calculated by the equation: FMD = (diameter hyperemia – diameter baseline) \* 100 / diameter baseline. A value of 8.1% suggesting a near normal value (>8%) was found.

The first step of a carotid ultrasound test is to identify plaques via B-mode as referred above. Addition of color Doppler enables identification of origin and course of the internal carotid artery and a differentiation between severe stenosis and occlusion. Stenotic areas are identified in the presence of the "aliasing" phenomenon occurring due to high velocities in the center of the stenotic lumen and post-stenotic flow disturbances. Flow velocities in the spectral analysis are the main parameters used for evaluating the severity of carotid stenosis. Flow velocity must be sampled through the whole area of presumed stenosis until the distal end of the plaque is seen to ensure that the site of the highest velocity has been detected. Compared to angiographic data, a wide range of flow velocities was recorded for any given degree of angiographic stenosis so that the sensitivity and specificity of the method may vary [59]. A better correlation to angiographic determined stenoses is achieved by assessing the peak systolic velocity in the internal carotid artery and the ratio of the peak systolic velocity in the internal carotid artery to that in the ipsilateral common carotid artery as proposed by the current guidelines [60]. Based on Doppler sonography, carotid stenoses are classified into two grades: Grade 1- with the rate of stenosis measuring between 50% to 69% and Grade 2 measuring 70-99%, which also represents a severe non-occlusive disease. In equivocal cases, further imaging methods may be additionally used. In Table 1 the sonographic criteria for grading of carotid artery stenosis

An ultrasound examination for detection of carotid stenoses and plaques and evaluation of the intima-media thickness should be performed in hypertensive patients with concomitant risk factors such as smoking, dyslipidemia, diabetes, obesity and family history of cardiovas‐ cular disease. The results can be useful for re-assessing CVD risk in some asymptomatic patients and consequently re-assessing therapeutic strategies. For accurate results, strict attention to quality control in image acquisition, measurement and interpretation are neces‐

Endothelial function is linked to cardiovascular risk factors and provides prognostic informa‐ tion for cardiovascular diseases [61]. Endothelial dysfunction is regarded as the initial step of atherosclerosis and therefore as the earliest detectable manifestation of vascular end-organ

**Grade of Stenosis Peak systolic velocity and visible criteria** no stenosis < 125 cm/s and no visible plaque or IMT < 50% < 125cm/s with visible plaque or IMT 50-69% 125 – 230 cm/s with visible plaque

> 70% to near occlusion > 230cm/s with visible plaque and lumen narrowing

100% No detectable patent lumen and flow is seen

**Table 1.** Grading of internal carotid artery stenosis upon Doppler velocities and B-mode

**6. Flow mediated dilation**

are summarized.

108 Advancements and Breakthroughs in Ultrasound Imaging

sary.

By using invasive and non-invasive methods impaired endothelial function has been found in uncomplicated hypertensive patients [62, 63]. In one prospective trial a reduction of blood pressure in response to antihypertensive treatment leads to improvement of the FMD sug‐ gesting a beneficial effect of antihypertensive treatment on endothelial function [64]. Several other large trials have found relationships between endothelial dysfunction assessed by FMD and prognostic markers of cardiovascular disease and atherosclerosis [65, 66]. Although the FMD test has opened a new field in the clinical research of conduit artery endothelial biology, some practical challenges of this technique have prevented its broad use in daily clinical practice so far. The most important of these are the need for highly trained operators, the timeconsuming analysis of results and the care required to minimize environmental or physiolog‐ ical influences such as eating, caffeine ingestion and variations of temperature [67].

**Figure 1.** Ultrasound images during testing of the flow mediated dilation. A slightly increase of the brachial diameter from 5.44mm at baseline to 5.88mm under hyperemia was recorded. The Doppler flow shows an increase of the blood flow after deflation of the cuff (hyperemia).
