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(The FASEB Journal. 2007;21:965.11)
© 2007 FASEB
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965.11

Regulation of blood pressure during head movement in the anaesthetized giraffe

Emil Toft Brøndum1, Tobias Wang2, Michael Hasenkam3, Hans Nygaard3, Niels H Secher4, Karin K Petersen5, Rikke Buhl6 and Christian Aalkjær1

1 Institute of Physiology and Biophysics,
2 Institute of Zoophysiology, University of Aarhus, Ole Worms Alle build. 1160, Århus C, Denmark,
3 University of Aarhus, Institute of Clinical Science, Skejby University Hospital, Denmark,
4 Rigshospitalet, Dept. of Anaesthesiology, Copenhagen Ø, Denmark,
5 Skejby University Hospital, Dept. of Radiology, Århus, Denmark,
6 Royal Veterinary and Agricultural University, Department of Large Animal Science, Copenhagen, Denmark

ABSTRACT

The giraffe experiences great cardiovascular challenges. When it lowers its head to drink, arterial pressure at the brain is expected to increase dramatically. This study investigated how blood pressure is regulated when lowering the head of anaesthetized giraffe.

METHODS: We measured pressure by insertion of catheters at the central part of the carotid artery and jugular vein of 5 anaesthetized spontaneously breathing giraffes, suspended in upright position. Changes in jugular cross sectional area were visualized by ultrasound (US).

RESULTS: When the giraffes head was lowered below heart level, the central arterial pressure (CAP) decreased from 205 ± 14 mmHg to 139 ± 18 mmHg, and central venous pressure (CVP) fell 2.9 ± 1.2 mmHg. US images revealed significant increase of the cross section of the cranial part of the jugular veins from 0.12 ± 0.04 cm2 to 3.16 ± 0.59 cm2, and thus an accumulation of estimated 5L of blood.

CONCLUSION: When the giraffe lowers its head, central blood volume falls and the associated reduction in cardiac filling lowers CAP by 60 mmHg. This may contribute to protection of the brain capillaries. When the giraffe lifts the head, the vein collapses and the accumulated blood is returned to the central circulation, increasing preload. Our study shows that the Starling mechanism may be involved in protecting the giraffe’s brain when lowering the head.





This Article
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