Aortic muscle cells in an oblique position

November 18^th, 2021

The smooth muscle of the aorta does not wind in the vessel wall in an exact circle, but with a slight slant, reports Gerhard Holzapfel of the Institute of Biomechanics. It was apparently oriented this way in evolution to optimize the biomechanical behavior of the aorta. He and colleagues created a computer model of the three-layered vessel. The study appeared in the Royal Society journal Proceedings A.

A human aorta is composed of three layers, Holzapfel explained. First, there is a matrix layer that has rubber-like properties. Another layer has long protein fibers (collagen layer) embedded in different directions, he said. Third, there is a layer of smooth "slow muscle."

A team led by Holzapfel analyzed these layers with imaging techniques and made complex calculations to simulate their behavior in the computer model. "However, these can be solved very efficiently," the researcher said, adding that this would make it possible to model "with pinpoint accuracy" how the aorta behaves mechanically.

It is striking that the muscle cells of the aorta are not arranged tangentially, i.e., in the direction of the vessel's circumference, as previously believed, but "inclined outward a bit," Holzapfel said: "We don't yet understand why nature has laid them out in this direction, but it is certainly a matter of functional optimization and the best possible alignment."