Although the aorta normally functions under radial compressive stresses associated with lumen blood pressure, these results show that the aorta tears radially at a much lower value of stress than would have been predicted from previous studies that have reported longitudinal and circumferential Young's modulus. This could explain why dissections propagate readily once the initial tear occurs.
Lumen area, ellipticity, and wall thickness were measured in the aortoiliac bifurcations obtained at autopsy from 14 patients aged between 1 day and 76 years. The method involved freezing pressure-fixed, stained bifurcations on the stage of a refrigerated microtome and then looking at the block face while sections were removed. Area change was normalized over segment length to produce a value of either taper (narrowing, in mm2/mm), or flare (expansion). The aortoiliac bifurcations were divided into three regions based on the area changes: an apical region corresponding to the bifurcation apex (taper = 2.96 +/- 0.80 mm2/mm), a preapical region (flare = 3.58 +/- 0.87 mm2/mm), and the postapical region (flare = 0.82 +/- 0.80 mm2/mm). Preapical lumen ellipticity showed that the anterio-posterior diameter was always less than the lateral diameter, while the degree of ellipticity increased with age. Average circumferential wall thickness, assessed in polar coordinates, decreased between 0 degree (right lateral) and 120 degrees, while a significant increase in wall thickness was present between 120 degrees and 200 degrees. The most striking difference was found in the 1-day-old, which was very thin posteriorly. This detailed geometric analysis of the aortoiliac bifurcation suggests that taper, flare, and variations in both circumferential and longitudinal wall thickness need to be considered when trying to correlate physical factors in the aorta with the precise location of atherosclerotic lesions and wall remodeling.
This article describes the framework and strategies that the London Health Sciences Centre has developed to foster trusting and collaborative relationships with its regional partners in Southwestern Ontario. A four-phase approach was used to identify, implement and evaluate system-wide opportunities to improve the integration of clinical care in Southwestern Ontario. Specific case studies are illustrated that used this framework to improve both access to patient services and length of stay, while positively affecting operating resources.
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