Experimental system for<i>ex vivo</i>measurement of murine aortic stiffness

While vascular stiffness is universally studied using pulse wave velocity, this method overestimates the stiffness of small calibre blood vessels. We have developed and rigorously validated an ex vivo system for measuring stiffness of the mouse aorta. The system consists of a temperature-controlled tissue bath, a pressurization loop and a helium-neon laser micrometer. We harvested thoracic aortas from 8 (n = 56), 11 (n = 6) and 14 (n = 6) week male C57BL/6J mice, mounted them within a tissue chamber and applied an intraluminal pressure waveform while measuring mid vessel outer diameter. Vessel stiffness (E(p), mmHg) was calculated from the pressure-diameter response. Vessels were then stained for endothelial cells, smooth muscle cells, elastin fibres and collagen. The data indicate highly reproducible stiffness measurements in 8 week mice (E(p) = 602.4 +/- 160.2; p = 0.934), age-related stiffening between 11 and 14 week mice (11 week E(p) = 646.9 +/- 62.4, 14 week E(p) = 795.4 +/- 87.5, p = 0.008), and a morphologically intact vessel wall. These results represent the first ex vivo measurements of murine aortic stiffness and illustrate that our methods are feasible and reliable. Since we demonstrate that the system is sensitive to age-related stiffening and does not damage the vessel, this approach is useful for investigating the pathophysiology of vascular disease from biomechanical and histological perspectives.