HACKENSACK, N.J. —  The biggest danger for magician David Blaine when he hangs upside down above New York's Central Park for 60 hours next week? Going blind.

That's the analysis of Dr. Massimo Napolitano of the Hackensack University Medical Center in New Jersey. He is the chief of vascular surgery and is advising Blaine on the stunt.

Napolitano told the Bergen Record for a story Saturday that hanging upside down for a long time increases blood pressure in the head, especially in the eyes. That could lead to blindness.

The doctor doesn't say how long the blindness could last, but he says there's also a risk of swelling and cramps in internal organs.

Nevertheless, Napolitano says the stunt could yield valuable data for doctors.