Mads F. Bertelsen1, DVM, DVSc, DACZM; Carsten Grøndahl1, DVM, PhD; Helle B. Hydeskov1, DVM; Cathrine D. Sauer1, MSc; Tobias Wang2, MSc, PhD; Christian Aalkjaer2, MD, PhD; Emil T. Brøndum2, MSc, PhD; Niklas Telinius2, MD; J. Michael Hasenkam, MD, PhD,2 Morten Smerup, MD, PhD,2 Jonas Funder2, MD, PhD; Arne Hoerlyck2, MD, PhD; Karin K. Petersen2, MD, PhD; Mads Damkjær3, MD, PhD; Peter Bie3, MD, PhD; Ulrik Baandrup4, MD, PhD; Kristine Østergaard4, MSc; Niels H. Secher5, MD, PhD; Marx Runge5; Peter Nissen5,; M. Axelsson6, MSc, PhD; G. Frik Stegman7, BVSc, MMedVet (Anes), DECVA
1Center for Zoo and Wild Animal Health, Copenhagen Zoo, Roskildevej 38, DK-2000 Frederiksberg, Denmark; 2Aarhus University, Aarhus C, Denmark; 3University of Southern Denmark, Odense, Denmark; 4Aalborg University, Hjørring, Denmark; 5Copenhagen University, Copenhagen, Denmark; 6University of Gotenborg, Sweden, 7University of Pretoria, Onderstepoort, South Africa
Abstract
Being the tallest animal on earth, the giraffe has an arterial blood pressure twice that of other mammals, and its cardiovascular anatomy and physiology has been subject to ample speculation and myths.
Using state-of-the-art methodology, we performed hemodynamic measurements in 24 anesthetized giraffes, and studied the cardiovascular anatomy of 35 freshly dead giraffes.
Relative heart mass resembles that of most other mammals (≈0.5% of BW), but the heart can generate high pressures because of smaller inner ventricular radii and a thickened left ventricular wall. As a consequence, stroke volume and cardiac output are lower than in similar-sized mammals (≈34 ml/(min·kg BW)). Blood volume is unusually low (≈5.6% of BW) as is the compliance of the vascular system.
When the head of the anesthetized giraffe is lowered, blood pressure at head-level peaks, before returning to much lower values. The lowering of the pressures coincides with pooling of blood in the compliant jugular veins, leading to a decreased cardiac preload and consequently lower systemic blood pressure. Similarly, even a small volume depletion causes an immediate and marked reduction in blood pressure. As a consequence of this mechanism, the arterial pressure at head level is maintained at or near 100 mm Hg, and the central blood pressure is directly proportional to the position of the head relative to the heart.
Considerable ventilation/perfusion mismatch prevails when the giraffe is placed in lateral recumbency, but not when suspended upright.
This data confirms the conventional wisdom that the anesthetized giraffe should be placed as sternally as possible with the head elevated.
Literature Cited
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