Blood Pressure Responses of Wild Giraffes Studied by Radio Telemetry

Citters, Robert L. Van; Kemper, W S; Franklin, Dean

doi:10.1126/science.152.3720.384

Cited by 45 publications

(32 citation statements)

References 3 publications

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“…Mean systolic pressure, measured with a cuff around the tail, increased from 110 to 137 mm Hg, or less than expected. A similar discrepancy was found for dogs [35] and giraffes [24,67,68]. In all three examples posture-dependent changes in blood pressure were less than would be expected on hydrostatic grounds [67].…”

Section: Raising and Lowering The Headsupporting

confidence: 75%

“…A similar discrepancy was found for dogs [35] and giraffes [24,67,68]. In all three examples posture-dependent changes in blood pressure were less than would be expected on hydrostatic grounds [67]. While head elevation thus affects blood pressure it is clearly not the sole influence determining the effect of raising or lowering the head [51].…”

Section: Raising and Lowering The Headmentioning

confidence: 52%

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Fainting in animals

Dijk

2003

Clin Auton Res

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Fainting (syncope) is unconsciousness due to insufficient cerebral circulation in the context of a temporary failure of the systemic circulation. This paper firstly aims to discuss fainting in animals, and secondly to discuss animal physiology to broaden the understanding of human fainting. Of the three major syncope types (cardiac, orthostatic and reflex syncope), only cardiac syncope occurs in animals as in man, through arrhythmia or output failure. Man's orthostatic fainting tendency has been blamed on his upright posture. A comparison with animals shows that giraffes, tree climbing snakes, and animals that quickly raise and lower their heads face more serious gravitational circulatory challenges than man, but do not appear to faint. Merely carrying the brain above the heart does not explain a fainting tendency, as the human heart-to-brain height is smaller than that of many mammals with similar blood pressure. Two evolutionary novelties may be to blame: the proportion of cardiac output going upwards to the brain is much larger than in apes, and man's large legs suggest that the volume lost to venous pooling is also larger. Emotional factors play a role in many reflex syncope events. Tonic immobility ('feigning death','playing possum') is not a good model, as it concerns immobility as a survival strategy of an attentive brain, rather than unconsciousness due to circulatory breakdown. Whether orienting and defense responses form a valid model remains to be proven. Emotional fainting may be uniquely human; how mental processes can shut down the circulation and thereby the brain needs serious study, as it may hold the key to syncope prevention.

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Section: Raising and Lowering The Headsupporting

confidence: 75%

Section: Raising and Lowering The Headmentioning

confidence: 52%

Fainting in animals

Dijk

2003

Clin Auton Res

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“…There are 29 measurements of giraffe systemic blood pressure reported in the literature and they were made in animals that had a similarly wide range of body masses and of neck lengths and angles as our giraffes. These measurements give an average systemic blood pressure of 203±41mmHg (Goetz, 1955;Goetz et al, 1960;Patterson et al, 1957;1965;van Citters et al, 1966van Citters et al, , 19681969;McCalden et al, 1977;Millard et al, 1986;Hargens et al, 1987;Mitchell & Skinner, 1993;Linton et al, 1999). Using the same sources pressure at the head can be calculated to be 100±21mmHg (Mitchell & Skinner, 1993), which is the same as that in all other mammalian species and is the pressure required to achieve adequate cerebral perfusion (Schmidt-Nielsen, 1984).…”

Section: Discussionmentioning

confidence: 99%

An allometric analysis of the giraffe cardiovascular system

Mitchell

Skinner

2009

Comparative Biochemistry and Physiology Part A: Molecular &

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There has been co-evolution of a long neck and high blood pressure in giraffes. How the cardiovascular system (CVS) has adapted to produce a high blood pressure, and how it compares with other similar sized mammals largely is unknown. We have measured body mass and heart structure in 56 giraffes of both genders ranging in body mass from 18kg to 1500kg, and developed allometric equations that relate changes in heart dimensions to growth and to cardiovascular function. Predictions made from these equations match measurements made in giraffes. We have found that heart mass increases as body mass increases but it has a relative mass of 0.51±0.7% of body mass which is the same as that in other mammals. The left ventricular and interventricular walls are hypertrophied and their thicknesses are linearly related to neck length.Systemic blood pressure increases as body mass and neck length increase and is twice that of mammals of the same body mass. Cardiac output is the same as, but peripheral resistance double that predicted for similar sized mammals. We have concluded that increasing hydrostatic pressure of the column of blood during neck elongation results in cardiac hypertrophy and concurrent hypertrophy of arteriole walls raising peripheral resistance, with an increase in blood pressure following.

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“…Giraffes are the tallest extant animals on Earth and are renowned for their high mean arterial blood pressure (Pa) at heart level (>300 mmHg in systole), which provides for typical mammalian cerebral perfusion pressures even when the brain is positioned several metres above the heart (Goetz and Budtz-Olsen, 1955;Van Citters et al, 1966, 1969Mitchell et al, 2006;Brøndum et al, 2009). In a series of legendary studies on the influences of posture and gravity on the cardiovascular systems of giraffes, Goetz and colleagues reported that the high mean Pa is achieved by virtue of an exceptionally large heart (Goetz, 1955;Goetz and Keen, 1957).…”

Section: Introductionmentioning

confidence: 99%

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

Smerup

Damkjær

Brøndum

et al. 2015

Journal of Experimental Biology

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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.

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Blood Pressure Responses of Wild Giraffes Studied by Radio Telemetry

Cited by 45 publications

References 3 publications

Fainting in animals

Fainting in animals

An allometric analysis of the giraffe cardiovascular system

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

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