Blood pressure and flow rate in the giraffe jugular vein
Experimental measurements in the jugular veins of upright giraffes have shown that the internal pressure is somewhat above atmospheric and increases with height above the heart. A simple model of steady viscous flow in an inverted U-tube shows that these observations are inconsistent with a model in which the blood vessels in the head and neck are effectively rigid and the system resembles a siphon. Instead, the observations indicate that the veins are collapsed and have a high resistance to