Researchers have stumbled on a vital discovery of how mesh-like arterial network dilates to restore blood supply to tissue starved of nutrients and oxygen after a stroke, holding out promise of treating such patients.

"This is optimistic news," said David Kleinfeld, physics professor at the University of California, San Diego (UCSD), whose group studies blood flow in animal models of stroke.

Damage from stroke can continue for hours or even days as compromised brain tissue surrounding the core injury succumbs to deprivation of oxygen and nutrients.

"This is the area doctors are trying to protect after a stroke," said Andy Shih, a postdoctoral fellow in Kleinfeld's group who conducted the experiments. "Those neurons are teetering on the edge of death and survival."

Previous work with animal models had found that blood flow can persistently slow in the aftermath of a stroke, which would hinder the delivery of drugs that might help recovery. But those studies only measured the speed of the blood.

By measuring both the speed of blood cells moving through individual small arteries and the diametres of the same vessels, the scientists found that the arteries dilate to maintain a constant delivery of blood cells.

"You find that the velocity has gone down, but that the diametre-on-average exactly compensates," Kleinfeld said.

Patrick Drew and Philbert Tsai in Kleinfeld's group, and Beth Friedman and Patrick Lyden, neuroscientist at UCSD School of Medicine co-authored the paper, said an UCSD report written by Susan Brown.

Lyden, whose contributions to a 1995 study proved that the drug tPA can reverse the course of stroke when administered promptly, also directs the UCSD Stroke Centre.

Their findings were published in the Journal of Cerebral Blood Flow and Metabolism.