Layman Description:

Being the tallest living animals, giraffes are endowed with a mean arterial pressure (MAP) twice as high as other mammals, including humans. The high MAP ensures adequate cerebral perfusion. However, the pressure distribution changes enormously between postures, and most significantly when comparing head-high to head-low postures. Moreover the hydrostatic pressure differences within the giraffe cardiovascular system are enormous.

In humans, a high mean arterial pressure is associated with numerous health related problems. The high pressure of the giraffe cardiovascular system undoubtedly causes serious challenges to both the heart and the systemic vasculature. Mechanisms must have evolved to protect the giraffe cardiovascular system from the adverse effects of a high MAP. The present thesis aims to unveil some of the protective mechanisms in the cardiovascular system in the giraffe and to gain knowledge of the evolutionary adaptations accompanying the highest known MAP of any mammals.

Three expeditions to South Africa were undertaken by the DaGiR team (Danish Cardiovascular Giraffe Research programme) to execute both physiological and morphological studies of the giraffe. The thesis has its main focus on the morphology of the heart, the conduit arteries of the lower extremeties, the neck and abdominal large veins (jugular and inferior caval vein) and the carotid artery. Using stereological methods, quantitative morphology of hearts, arteries and veins were examined and analysed. The morphological results were correlated with functional data. The morphological data reveal that the left ventricle of the giraffe heart posseses significant differences in quantitative terms from other mammals. The systemic vasculature shows structural specialisations which we suggest to have regulative function. In addition, the structure of arteries and veins below heart level point to a system with a low compliance, which would be in accordance with the high MAP and a low blood volume.

About Myths and Facts in the Cardiovascular System of the Giraffe