A model for time-dependent flow in (giraffe jugular) veins: uniform tube properties
Computations are reported for a one-dimensional model of time-dependent flow in collapsible tubes representing long mammalian veins. The tubes are taken to have uniform intrinsic properties and we concentrate on the effect of longitudinal gravity. The main application is to the jugular vein of the upright giraffe, with given inflow rate from the head, a […]
How giraffes prevent oedema
An upright giraffe, by analogy with humans, ought to suffer massive oedema in its feet; moreover, when it lowers its head to drink, the blood should rush down into it and be unable to flow up again. New pressure measurements reported on page 59 of this issue by Hargens et al. Show why neither of […]
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 […]
Cerebral perfusion pressure in Giraffe: Modelling the effects of head-raising and – lowering
Loss of consciousness caused by positional changes of the head results from reduced cerebral blood flow (CBF). CBF is related to cerebral perfusion pressure (CPP). CPP is the difference between mean arterial pressure (MAP) at the head and intracranial pressure (ICP). The positional change of the giraffe head between ground level and standing upright is […]
The structure and function of giraffe jugular vein valves
When a giraffe (Giraffa camelopardalis) lowers its head to drink, blood could enter the jugular vein from the inferior vena cava or regurgitate from the jugular veins into the cranial veins. We investigated the anatomy of jugular valves in giraffes to establish if they could prevent either of these regurgitations. Jugular vein length and intervalve […]