Washington, Feb 1 : Experts at Johns Hopkins have figured out how night-hunting owls can almost fully rotate their heads - by as much as 270 degrees in either direction - without damaging the delicate blood vessels in their necks and heads, and without cutting off blood supply to their brains.

In what may be the first use of angiography, CT scans and medical illustrations to examine the anatomy of a dozen of the big-eyed birds, the Johns Hopkins team, led by medical illustrator Fabian de Kok-Mercado, M. A., a recent graduate student in the Department of Art as Applied to Medicine, found four major biological adaptations designed to prevent injury from rotational head movements.

The variations are all to the strigid animals' bone structure and vascular network needed to support its top-heavy head.

Sudden gyrations of the head and neck in humans have been known to stretch and tear blood vessel linings, producing clots that can break off and cause a deadly embolism or stroke. Researchers say these injuries are commonplace, often resulting from whiplashing car accidents, but also after jarring roller coaster rides and chiropractic manipulations gone awry.

To solve the puzzle, the Johns Hopkins team studied the bone structure and complex vasculature in the heads and necks of snowy, barred and great horned owls after their deaths from natural causes. An injectible contrast dye was used to enhance X-ray imaging of the birds' blood vessels, which were then meticulously dissected, drawn and scanned to allow detailed analysis.

The most striking team finding came after researchers injected dye into the owls' arteries, mimicking blood flow, and manually turned the animals' heads. Blood vessels at the base of the head, just under the jaw bone, kept getting larger and larger, as more of the dye entered, and before the fluid pooled in reservoirs. This contrasted starkly with human anatomical ability, where arteries generally tend to get smaller and smaller, and do not balloon as they branch out.

Researchers say these contractile blood reservoirs act as a trade-off, allowing owls to pool blood to meet the energy needs of their large brains and eyes, while they rotate their heads. The supporting vascular network, with its many interconnections and adaptations, helps minimize any interruption in blood flow.

The team also found that the owl's vertebral artery enters the neck higher up than in other birds - going in at the owl's 12th cervical vertebrae instead of the owl's 14th cervical vertebrae - allowing for more vessel room and slack.

Futher de Kok-Mercado and neuroradiologist Philippe Gailloud, study senior investigator and interventional, found small vessel connections between the carotid and vertebral arteries - not usually seen in adult humans - that allow blood to be exchanged between the two blood vessels.

The researchers say these so-called anastomoses, including a vessel connection called a patent trigeminal artery, allow for uninterrupted blood flow to the brain, even if one route is blocked during extreme neck rotation.

The team's findings are acknowledged in the Feb. 1 issue of the journal Science, as first-place prize winners in the posters and graphics category of the National Science Foundation's 2012 International Science and Engineering Visualization Challenge. (ANI)