The thick left ventricular wall of the giraffe heart normalises wall tension, but limits stroke volume and cardiac output

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  • Morten Holdgaard Smerup
  • ,
  • Mads Damkjær, Department of Cardiovascular and Renal Research, University of Southern Denmark, Odense, Denmark
  • Emil Brøndum
  • Ulrik T. Baandrup, Department of Pathology, Center for Clinical Research, Vendsyssel Hospital, Aalborg University, Denmark
  • Steen Buus Kristiansen
  • Hans Nygaard
  • Christian Aalkjær
  • Cathrine Sauer
  • ,
  • Rasmus Buchanan
  • Mads Frost Bertelsen, Centre for Zoo and Wild Animal Health, Denmark
  • Kristine Hovkjær Østergaard, Det Sundhedsvidenskabelige Fakultet, Denmark
  • Carsten Grøndahl, Centre for Zoo and Wild Animal Health, Denmark
  • Geoffrey Candy, Department of Physiology and Medicine, University of the Witwatersrand, Johannesburg, South Africa
  • J Michael Hasenkam
  • Niels H Secher, Department of Anesthesiology, Rigshospitalet, Copenhagen
  • ,
  • Peter Bie, Department of Cardiovascular and Renal Research, University of Southern Denmark, Odense, Denmark
  • Tobias Wang

Giraffes - the tallest extant animals on Earth - are renowned for their high central arterial blood pressure, which is necessary to secure brain perfusion. The pressure which may exceed 300 mmHg has historically been attributed to an exceptionally large heart. Recently, this has been refuted by several studies demonstrating that the mass of giraffe heart is similar to that of other mammals when expressed relative to body mass. It remains enigmatic, however, how the normal-sized giraffe heart generates such massive arterial pressures.We hypothesized that giraffe hearts have a small intraventricular cavity and a relatively thick ventricular wall, allowing for generation of high arterial pressures at normal left ventricular wall tension. In nine anaesthetized giraffes (495±38 kg), we determined in vivo ventricular dimensions using echocardiography along with intraventricular and aortic pressures to calculate left ventricular wall stress. Cardiac output was also determined by inert gas rebreathing to provide an additional and independent estimate of stroke volume. Echocardiography and inert gas-rebreathing yielded similar cardiac outputs of 16.1±2.5 and 16.4±1.4 l min(-1), respectively. End-diastolic and end-systolic volumes were 521±61 ml and 228±42 ml, yielding an ejection fraction of 56±4%, and a stroke volume of 0.59 ml kg(-1). Left ventricular circumferential wall stress was 7.83±1.76 kPa. We conclude that, relative to body mass, a small left ventricular cavity and a low stroke volume characterizes the giraffe heart. The adaptations result in typical mammalian left ventricular wall tensions, but results in lowered cardiac output.

Original languageEnglish
JournalJournal of Experimental Biology
Pages (from-to)457-63
Number of pages7
Publication statusPublished - 2016

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