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Giraffe Stroke

December 21, 2006

Giraffes have big-time blood pressure to get blood to their heads. So why don’t they burst a blood vessel when they bend down?


How giraffes block a head rush. I’m Bob Hirshon and this is Science Update.

It takes a lot of pressure to pump blood from giraffes’ hearts to their heads. So listener Matthew Vonderahe from Seattle, Washington, wants to know why bending their heads down doesn’t cause a stroke. Giraffe circulation expert Alan Hargens of the University of California-San Diego explains that their brains and spinal cords are surrounded by fluid, just like ours. When they bend over, that fluid rushes to their heads, and squeezes the swelling blood vessels from the outside.

ALAN HARGENS (University of California, San Diego):
So when they bend head-down to, say, drink water, the elevation of blood pressure due to the head-down tilt could be counteracted by the increase in cerebro-spinal fluid pressure.

Even so, he says giraffes generally don’t keep their heads down for long, even when they’re sleeping. If you’ve got a science question, call us at 1-800-WHY-ISIT.
I’m Bob Hirshon, for AAAS, the science society.