How giraffes keep the pressure up

[Dann Pigdon <dannj@alphalink.com.au>]

This may be of interest to those sauropodomorphiles out there:

Mitchell, G., Maloney, S. K., Mitchell, D.
Keegan, D. J. (2006). The origin of mean
arterial and jugular venous blood pressures
giraffes. J. Exp. Biol. 209, 2515-2524.

The team built a mechanical model of a giraffe's neck and head,  
consisting of a 1660 mm long `carotid artery' tube, a 1638 mm long  
collapsible `jugular' tube, a linking tube to simulate blood flow  
through the brain, and a pump that simulated the heart. Adjusting the  
relative positions of the bottoms of the carotid and jugular tubes to  
create a siphon, the team tested several permutations of rigid and  
flexible blood vessels, and found that the siphon failed to deliver  
sufficient pressure. However, when the team activated the pump to  
simulate the heart's intrinsic hydrostatic pressure, they successfully  
generated pressures similar to those measured in the giraffe's carotid  
artery. And when the team constricted the lowest portion of the  
jugular tube, they found that the blood pressure rose dramatically.  
They suggest that by constricting the jugular at this point, giraffes  
could maintain sufficient blood pressure, when they raise their heads  
after drinking, to prevent themselves from passing out.

http://jeb.biologists.org/cgi/content/full/209/13/iii

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Dann Pigdon
GIS / Archaeologist         http://heretichides.soffiles.com
Melbourne, Australia        http://www.geocities.com/dannsdinosaurs
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