Wild Arterial Rides

Blood is known to spiral as it flows through arteries, but researchers at a Royal Academy of Engineering conference announced yesterday in London that these helical streams themselves whirl like a corkscrew. What's more, the turns and branches of blood vessels encourage the swirling flow, which scours them of plaque and helps prevent atherosclerosis.

Until recently, researchers have lacked the computer power to accurately model blood flow in complex, three-dimensional geometries, says Spencer Sherwin, a fluid dynamicist at London's Imperial College of Science, Technology and Medicine. But a new computer program written by Sherwin and his colleagues appears to have at last succeeded in accurately modeling arterial blood flow: Their computations correspond well with MRI data on blood velocity within arteries, says Danesh Tafti of the National Center for Supercomputing Applications in Champaign, Illinois.

The new program could pave the way for more durable arterial grafts, natural or artificial replacements for nonfunctioning arteries, says team-member Colin Caro, a physiologist also at Imperial College. About half of all arterial grafts fail within 10 years, after becoming blocked by a thickening of the inner wall. This might happen because surgeons tend to join grafts at right angles to vessel walls in a single flat plane, rather than having them curve in like a freeway onramp as natural vessels do.

Sherwin's team now plans to use simulations and MRI scans of actual arteries to determine the optimum angle of arterial grafts to maintain swirling blood flow that could prevent blockages.

"The blood flow findings are obviously important for improving arterial graft construction," says Michael Bettmann, a cardiovascular specialist at Dartmouth-Hitchcock Medical Center of Dartmouth in New Hampshire, "but they also may be relevant to evolving new techniques, primarily nonoperative ones for treating peripheral arterial diseases."