Thicker than water. A normal carotid artery shows swirling flow patterns where it bifurcates. Wall shear stress (left image) and mechanical stress (right image) distributions show high-risk regions where shear stress is low and mechanical stress hi

How the Blood Flows

It was bloody complicated, but scientists at Imperial College in London have come up with the most detailed computer model yet of how blood courses through human arteries. The model, which has been submitted for publication, may help scientists gain new insights into the interaction of factors that influence the body's cardiovascular plumbing, from the pulsing of blood to the curves, branches, and flexibility of arteries.

Researchers fed images of blood flow and blood vessel architecture into a computer model that combines a computational fluid dynamics program and a solid mechanics program, says engineer Xu Yun. The result is a detailed image of how blood flow varies in three dimensions as the heart beats. Scientists already knew that, just as with pipes, pressures are greater at blood vessel junctures. But the researchers were able to separate shear stress--which works on the cells lining vessel walls--from mechanical stress--the distending effect of blood pressure on vessels. A new finding, Xu says, is that some curved or branching stretches of an artery are simultaneously exposed to low shear and high mechanical stress--and that is where the blockages that cause heart disease seem to develop.

The images ultimately may help clinicians make predictions about individual patients, Xu says. "Does the geometry of a particular vessel predispose someone to arterial disease, for example? We will be able to quantify the areas where in the past people have been able only to debate and theorize."

Related site

Xu Yun's home page