A blood vessel made of silicone simulates an aneurysm. | Image: Utku Gülan.

At what point is an aneurysm so threatening it has to be operated on? If doctors could predict this better, they could save lives. Because if these balloon-like protrusions enter our body’s main arteries or burst altogether, we are put in acute danger. This is especially the case when the bulge occurs in the ascending aorta, an artery near the heart. But operating on such aneurysms can itself cause severe complications.

Markus Holzner is a professor of environmental fluid mechanics at ETH Zurich. Together with his team of researchers, he’s been searching for parameters to help us to predict in individual cases whether or not it’s urgent to operate on an aneurysm. To do this, they have been taking a closer look at the bloodstream. During their tests they relied on a silicone vessel that corresponds in every detail to the bulging ascending aorta of a real patient. But wouldn’t computer simulations have been simpler? “In theory, yes”, says Holzner, “but since the bloodstream is pulsating, the aorta is constantly altering its geometry. To compute such shifts would be incredibly complicated”.

As his team has discovered, blood creates strong turbulence and vortices in the section of the aorta that is bulging abnormally. There is also a loss of blood pressure and of motion energy. “We now want to ascertain in further studies whether one or all of these parameters are reliable signs of the threat of an aortic aneurysm”, explains Holzner. These could be measured with an MRI, and could thus be of considerable diagnostic use.