Department of Clinical Medicine

TY - JOUR

T1 - The thick left ventricular wall of the giraffe heart normalises wall tension, but limits stroke volume and cardiac output

AU - Smerup, Morten Holdgaard

AU - Damkjær, Mads

AU - Brøndum, Emil

AU - Baandrup, Ulrik T.

AU - Kristiansen, Steen Buus

AU - Nygaard, Hans

AU - Aalkjær, Christian

AU - Sauer, Cathrine

AU - Buchanan, Rasmus

AU - Bertelsen, Mads Frost

AU - Østergaard, Kristine Hovkjær

AU - Grøndahl, Carsten

AU - Candy, Geoffrey

AU - Hasenkam, J Michael

AU - Secher, Niels H

AU - Bie, Peter

AU - Wang, Tobias

N1 - © 2015. Published by The Company of Biologists Ltd.

PY - 2016

Y1 - 2016

N2 - 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.

AB - 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.

U2 - 10.1242/jeb.132753

DO - 10.1242/jeb.132753

M3 - Journal article

C2 - 26643090

VL - 49

SP - 457

EP - 463

JO - The Journal of Experimental Biology

JF - The Journal of Experimental Biology

SN - 0022-0949

IS - 3

ER -