Effect of calcification and formalin fixation on in vitro distensibility of human femoral arteries.

To determine the effect of calcification on the distensibility of human arteries, we measured changes in lumen cross-sectional area as a function of pressure in excised segments of calcified and noncalcified human femoral arteries with the use of intravascular ultrasound. Cross-sectional area at zero pressure was greater in calcified artery segments (22.1 +/- 4.4 mm2) compared with noncalcified arteries (18.9 +/- 2.4 mm2). Calcified arteries were significantly less distensible than noncalcified arteries (2.5-fold). To assess the validity of mechanical tests of fixed arteries, pressure-area relations were also obtained after formalin fixation: mean unstressed cross-sectional area decreased significantly in noncalcified arteries (24%) but did not change significantly in calcified arteries. Formalin fixation decreased distensibility significantly (68%) in noncalcified arteries but not in calcified arteries. These results indicate that decreased lumen size and increased rigidity are induced by formalin fixation in noncalcified arteries but not in calcified arteries, and that this is attributable to the lower distensibility of calcified arteries before fixation. Because histologic examination is commonly used to evaluate severity of lumen narrowing in studies of atherosclerosis, this differential effect of formalin fixation may cause calcified arteries to appear less severely obstructed than noncalcified arteries.