Jonas Amstrup Funder1,10, Carl Christian Danielsen2, Ulrik Baandrup3,4, Bo Martin Bibby5, Ted Carl Andelius8, Emil Toft Brøndum6, Tobias Wang7, J. Michael Hasenkam8,91Department of Surgery, Aarhus University Hospital, Aarhus, Denmark
2Department of Biomedicin, Aarhus University, Aarhus, Denmark
3Centre for Clinical Research, Aalborg University, Denmark
4Department of Clinical Medicine, North Denmark Regional Hospital, Denmark
5Department of Biostatistics, Aarhus University, Aarhus, Denmark
6Department of Oto-Rhino-Laryngology, Aarhus University Hospital, Aarhus, Denmark
7Zoophysiology, Department of Bioscience, Aarhus University, Denmark
8Department of Cardio-Thoracic and Vascular surgery, Aarhus University Hospital, Aarhus, Denmark
9Department of Surgery, University of Witwatersrand, Johannesburg, South Africa
10Electronic correspondence: firstname.lastname@example.org
Background and aim of the study: Heart valves which exist naturally in an extreme-pressure system must have evolved in a way to resist the stresses of high pressure. Giraffes are interesting as they naturally have a blood pressure twice that of humans. Thus, knowledge regarding giraffe heart valves may aid in developing techniques to design improved pressure-resistant biological heart valves.
Methods: Heart valves from 12 giraffes and 10 calves were explanted and subjected to either biomechanical or morphological examinations. Strips from the heart valves were subjected to cyclic loading tests, followed by failure tests. Thickness measurements and analyses of elastin and collagen content were also made. Valve specimens were stained with hematoxylin and eosin, elastic van Gieson stain, Masson’s trichrome and Fraser-Lendrum stain, as well as immunohistochemical reactions for morphological examinations.
Results: The aortic valve was shown to be 70% (95% CI 42-103%) stronger in the giraffe than in its bovine counterpart (p <0.001). No significant difference was found
between mitral or pulmonary valves. After normalization for collagen, no significant differences were found in strength between species. The giraffe aortic valve was found to be significantly stiffer than the bovine aortic valve (p <0.001), with no significant difference between mitral and pulmonary valves. On a dry weight basis, the aortic (10.9%), pulmonary (4.3%), and mitral valves (9.6%) of giraffes contained significantly more collagen than those of calves. The elastin contents of the pulmonary valves (2.5%) and aortic valves (1.5%) were also higher in giraffes.
Conclusion: The greater strength of the giraffe aortic valve is most likely due to a compact collagen construction. Both, collagen and elastin contents were higher in giraffes than in calves, which would make giraffe valves more resistant to the high-pressure forces. However, collagen also stiffens and thickens the valves. The mitral leaflets showed similar (but mostly insignificant) trends in strength, stiffness, and collagen content.
The Journal of Heart Valve Disease 2017;26:63-71
|How Heart Valves Evolve to Adapt to an Extreme-Pressure System: Morphologic and Biomechanical Properties of Giraffe Heart Valves|
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