An allometric analysis of the giraffe cardiovascular system
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 […]
Gravitational haemodynamics and oedema prevention in the giraffe
Because it is so tall, the giraffe, Giraffa camelopardalis, provides an important animal model for investigating adaptive mechanisms to orthostatic (gravitational) pressure changes. Previous physiological studies of the giraffe have concentrated on arterial blood pressures in the heart and neck. Briefly, these investigations revealed that arterial pressure near the giraffe heart is about twice that […]
Blood pressure and flow rate in the giraffe jugular vein
Experimental measurements in the jugular veins of upright giraffes have shown that the internal pressure is somewhat above atmospheric and increases with height above the heart. A simple model of steady viscous flow in an inverted U-tube shows that these observations are inconsistent with a model in which the blood vessels in the head and […]
Is the Flow in the Giraffe’s Jugular Vein a “Free” fall?
There is a controversy as to whether or not the heart works against gravity in the arteries to the head in the upright position. One view is that the gravitational effects in the neck arteries are counterbalanced by the gravitational effects in the veins of the neck and the heart does not do extra pressure […]
Does gravitational pressure of blood hinder flow to the brain of the giraffe?
Vascular pressure consists of the sum of two pressures: (a) pressure developed by the pumping of the ventricles against the resistance of vessels, designated as viscous flow pressure, and (b) pressure caused by gravity, traditionally called hydrostatic, better described as gravitational pressure. In a conduit, both of these pressures must be overcome when a liquid […]
Harvey Cushing and the regulation of blood pressure in giraffe, rat, and man: introducing ‘Cushing’s mechanism’
The fundamental mechanism that underlies essential hypertension is a high total peripheral resistance. We review here possible origins of high total peripheral resistance in physiologically hypertensive giraffes, spontaneously hypertensive rats and humans with essential hypertension. We propose that a common link could be reduced brainstem perfusion, as first suggested by Cushing in 1901. Any tendency […]
Pressure profile and morphology of the arteries along the giraffe limb
Giraffes are the tallest animals on earth and the effects of gravity on their cardiovascular system have puzzled physiologists for centuries. The authors measured arterial and venous pressure in the foreleg of anesthetized giraffes, suspended in upright standing position, and determined the ratio between tunica media and lumen areas along the length of the femoral/tibial […]
Haemodynamics of the jugular vein in the giraffe
Controversy cotinues over the haemodynamics of the circulation to and from the head of the giraffe. The recent study by Hargens et al. provides new information explaining the absence of oedema in the legs of the ambulant giraffe. But in sedated, standing giraffes the pressure gradient down the jugular vein is about one-tenth of, and […]
Jugular venous pooling during lowering of the head affects blood pressure of anesthetized giraffe
How blood flow and pressure to the giraffe’s brain are regulated when drinking remains debated. We measured simultaneous blood flow, pressure, and cross-sectional area in the carotid artery and jugular vein of five anesthetized and spontaneously breathing giraffes. The giraffes were suspended in the upright position so that we could lower the head. In the […]
Accuracy of noninvasive anesthetic monitoring in the anesthetized giraffe (Giraffe camelopardalis)
This study evaluated the accuracy of pulse oximetry, capnography, and oscillometric blood pressure during general anesthesia in giraffes (Giraffa camelopardalis). Thirty-two giraffes anesthetized for physiologic experiments were instrumented with a pulse oximeter transmittance probe positioned on the tongue and a capnograph sampling line placed at the oral end of the endotracheal tube. A human size […]