title: The thick left ventricular wall of the giraffe heart normalises wall tension, but limits stroke volume and cardiac output.
abstract: Giraffes--the tallest extant animals on Earth--are renowned for their high central arterial blood pressure, which is necessary to secure brain perfusion. Arterial pressure may exceed 300 mmHg and 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 thus remains unexplained 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, respectively, 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 produce a lowered cardiac output.
authors.affiliation: Department of Cardiothoracic Surgery, Rigshospitalet, 2100 Copenhagen, Denmark Department of Clinical Medicine, Aarhus University, 8000 Aarhus, Denmark.
authors.forename: Morten
authors.initials: M
authors.lastname: Smerup
authors.affiliation: Hans Christian Andersen Children's Hospital, 5000 Odense, Denmark Department of Cardiovascular and Renal Research, University of Southern Denmark, 5000 Odense, Denmark mdamkjaer@health.sdu.dk.
authors.forename: Mads
authors.initials: M
authors.lastname: Damkjær
authors.affiliation: Department of Biomedicine, Aarhus University, 8000 Aarhus, Denmark Department of Biomedical Sciences, Copenhagen University, 2200 Copenhagen, Denmark.
authors.forename: Emil
authors.initials: E
authors.lastname: Brøndum
authors.affiliation: Department of Pathology, Center for Clinical Research, Vendsyssel Hospital, Aalborg University, 9000 Aalborg, Denmark.
authors.forename: Ulrik T
authors.initials: UT
authors.lastname: Baandrup
authors.affiliation: Department of Cardiology, Aarhus University Hospital, 8200 Aarhus N, Denmark.
authors.forename: Steen Buus
authors.initials: SB
authors.lastname: Kristiansen
authors.affiliation: Department of Thoracic and Cardiovascular Surgery and Department of Clinical Medicine, Aarhus University, 8200 Aarhus N, Denmark.
authors.forename: Hans
authors.initials: H
authors.lastname: Nygaard
authors.affiliation: Department of Thoracic and Cardiovascular Surgery and Department of Clinical Medicine, Aarhus University, 8200 Aarhus N, Denmark.
authors.forename: Jonas
authors.initials: J
authors.lastname: Funder
authors.affiliation: Department of Biomedicine, Aarhus University, 8000 Aarhus, Denmark Department of Biomedical Sciences, Copenhagen University, 2200 Copenhagen, Denmark.
authors.forename: Christian
authors.initials: C
authors.lastname: Aalkjær
authors.affiliation: Centre for Zoo and Wild Animal Health, Copenhagen Zoo, 1870 Frederiksberg C, Denmark.
authors.forename: Cathrine
authors.initials: C
authors.lastname: Sauer
authors.affiliation: Zoophysiology, Department of Biological Sciences, Aarhus University, 8000 Aarhus C, Denmark.
authors.forename: Rasmus
authors.initials: R
authors.lastname: Buchanan
authors.affiliation: Centre for Zoo and Wild Animal Health, Copenhagen Zoo, 1870 Frederiksberg C, Denmark.
authors.forename: Mads Frost
authors.initials: MF
authors.lastname: Bertelsen
authors.affiliation: Department of Pathology, Center for Clinical Research, Vendsyssel Hospital, Aalborg University, 9000 Aalborg, Denmark.
authors.forename: Kristine
authors.initials: K
authors.lastname: Østergaard
authors.affiliation: Centre for Zoo and Wild Animal Health, Copenhagen Zoo, 1870 Frederiksberg C, Denmark.
authors.forename: Carsten
authors.initials: C
authors.lastname: Grøndahl
authors.affiliation: Department of Physiology and Medicine, University of the Witwatersrand, Parktown, 2193 Johannesburg, South Africa.
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Candy
authors.affiliation: Department of Thoracic and Cardiovascular Surgery and Department of Clinical Medicine, Aarhus University, 8200 Aarhus N, Denmark.
authors.forename: J Michael
authors.initials: JM
authors.lastname: Hasenkam
authors.affiliation: Department of Anesthesiology, Rigshospitalet, 2100 Copenhagen, Denmark.
authors.forename: Niels H
authors.initials: NH
authors.lastname: Secher
authors.affiliation: Department of Cardiovascular and Renal Research, University of Southern Denmark, 5000 Odense, Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Bie
authors.affiliation: Zoophysiology, Department of Biological Sciences, Aarhus University, 8000 Aarhus C, Denmark.
authors.forename: Tobias
authors.initials: T
authors.lastname: Wang
mesh_terms: D000818:Animals; D001794:Blood Pressure; D002302:Cardiac Output; D004452:Echocardiography / Q000662:veterinary; D000068276:Giraffes / Q000502:physiology*; D008297:Male; D013318:Stroke Volume; D016276:Ventricular Function
keywords: Cardiac output; Echocardiography; End diastolic volume; Left ventricle; Stroke volume