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SUMMARY
We measured carotid blood flow, and carotid and jugular pressure, and calculated resistance in the head up and head down position in a young giraffe. Resistance to flow increased during head raising and did not decrease as others have suggested. Relating this finding to the unique anatomy of the giraffe cerebral circulation we concluded that in the head-down position blood flow to the head is relatively uncontrolled but when the head is raised, intense extracranial vasoconstriction occurs which directs carotid blood via the occipito-vertebral anastomosis to the brain, thus preventing ‘fainting’.
We also compared body and brain temperature in two giraffes. Body temperature varied by up to 6 °C and brain temperature was up to 3 °C lower than body temperature. This difference implies a very effective nasal cooling system. We measured respiratory tract temperature in three giraffe and found that over a distance of 70 cm temperatures fall 7,0 °C.
A proposition that skin patches act as heat dissipating windows was also tested. Temperatures under patches and non-patches were measured at the depths of anastomotic channels (15 mm) and subcutaneous vessels (30 mm). Our data support the ‘window’ proposition. At 15 mm depth patch temperature is below rectal temperature while non-patch temperature at this depth is similar to rectal temperature. At 30 mm depth patch temperatures are lower than non-patch temperatures and non-patch temperatures are greater than rectal temperatures.