Relation between zero-stress state and branching order of porcine left coronary arterial tree

The left common coronary arterial trees of eight pig hearts were dissected. The zero-stress state (the state of the organ when the external loads are removed) of the coronary arteries was determined by first cutting the arter ies into short, ring-shaped segments perpendicular to the longitudinal axis of the blood vessel and then making a radial cut. This procedure caused th e ring to open into a sector whose opening angle (theta), internal and exte rnal lengths (circumferences), and wall thickness were measured. Morphometr ic and theta data were organized in the framework of a diameter-defined Str ahler system. We investigated 4 rings from the left common coronary artery (LCCA), 185 from the left anterior descending artery (LAD) and its branches , and 159 from the left circumflex artery (LCX) and its branches. The inner circumferences of the rings ranged over six orders for the LAD arterial tr ee and five orders for the LCX arterial tree, corresponding to a diameter r ange of about one order of magnitude for both arteries. theta demonstrates viscoelastic behavior and was measured 30 min after cutting. Our results sh ow that the inner and outer circumference and the wall thickness increase a s geometric sequences with the order number. theta is found to decrease lin early toward the smaller orders with a slope of 7.3 degrees/order in the ra nge of the six largest orders. Strain calculations showed that the inner pa rt of the arterial wall is in compression, whereas the outer part of the wa ll is in tension in the no-load (zero transmural pressure) state. This stud y provides basic data on the zero-stress state that are necessary for under standing the mechanics of the coronary artery.