Detection of Early Atherosclerosis in M. Fascicularis with Transcutaneous Ultrasonic Measurement of the Elastic Properties of the Common Carotid Artery

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The elastic properties of 22 common carotid arteries from 13 male cynomolgus monkeys (M. fascicularis) that were fed either a high cholesterol (test) diet or a standard monkey chow (control) diet for 18 months were measured noninvasively with 5MHz ultrasound. A B-mode image of the artery was obtained with a 32-element linear array transducer, and a single line of video ultrasonic information was selected for tracking the echoes from the adventitial side of the near wall to the lumen-intima interface of the far wall. This technique measured lumen diameter plus anterior wall thickness. The diastolic diameter (Dd) (mean ± SEM) of the test arteries was slightly larger than controls (2.9 ± 0.1 vs 2.5 ± 0.1 mm), whereas the fractional diameter change from diastole to systole (ΔD/Dd, where ΔD = diameter change) was slightly less (0.062 ± 0.010 vs 0.082 ± 0.011). Direct subclavian artery pulse pressure (ΔP) in the test animals (63 ± 4 mm Hg) was significantly greater than in the controls (41 ± 2 mm Hg), whereas there was no difference in diastolic pressure (85 ± 3 vs 81 ± 2), respectively. The pressure-strain elastic modulus Ep = (ΔP/ΔD) Dd was significantly greater in the test monkeys (182 ± 33 kPa) than in the controls (73 ± 9 kPa). Morphometric analysis of atherosclerosis revealed more connective tissue and intra- and extracellular lipids in the test arteries than in the controls. Based on the average of three cross-sections equally spaced along each common carotid artery, the intimal area and the maximal intimal thickness averaged 0.89 ± 0.16 mm2 and 0.26 ± 0.04 mm for the test monkeys compared to negligible intimae from the controls. Medial area also was significantly greater in the test monkeys (0.71 ± 0.03 mm2) compared to controls (0.57 ± 0.04 mm2). Percentage stenosis defined as intimal area/IEL area, where IEL area is that within the internal elastic lamina, showed the test arteries to have 30 ± 5% stenosis compared to 0% for the controls. However, dilatation appeared to compensate for any loss in lumen area due to intimal thickening. In this study, significant carotid artery stiffening associated with diet-induced atherosclerosis is demonstrated. This noninvasive technique may be useful in pediatrics and in preventive medicine for the detection of arterial stiffening associated with early progressive atherosclerotic lesions.

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