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First published online June 15, 2006
Journal of Experimental Biology 209, 2515-2524 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02277

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The origin of mean arterial and jugular venous blood pressures in giraffes

Graham Mitchell^1,*, Shane K. Maloney^2,3, Duncan Mitchell³ and D. James Keegan³

¹ Department of Zoology and Physiology, University of Wyoming, 1000 E University Avenue, Laramie, WY 82071, USA,
² Physiology: Biomedical and Chemical Science, University of Western Australia, Perth, Australia
³ Department of Physiology, University of the Witwatersrand, Johannesburg, South Africa

View larger version (19K): [in a new window]   Fig. 1. Giraffe jugular venous pressures (JVP) as measured by Hargens et al. (Hargens et al., 1987) (circles and solid line) and a linear regression line calculated from the data (broken line). The relationship between height in meters and JVP in mmHg is JVP=0.093xheight–0.022 (r=0.987). The linear regression predicts that right atrial pressure will be 0 mmHg, which is the measured value.

View larger version (19K): [in a new window]   Fig. 2. Profile of giraffe cranial pressures. Solid lines show known pressures using published data (Mitchell and Skinner, 1993; Hargens et al., 1987). Broken lines show pressures generated by the model, and are given in more detail in Table 2. Note that the model can replicate known giraffe jugular pressures, can replicate separately mean arterial pressure and mean cranial pressure, but cannot replicate all typical giraffe carotid and jugular pressures simultaneously.

View larger version (26K): [in a new window]   Fig. 3. A diagram of the model of the giraffe cranial circulation used. P1, P2, P3, P4, P5, P6 were sites of pressure measurement. R1, R2, R3 and R4 were sites where external pressure could be applied using a sphygmomanometer. A submerged pump and/or jugular limb extension tube was used to generate flow through the system. The jugular tube terminated outside the bath to allow for siphon operation, and bath water level was maintained with a valve-controlled constant inflow.

View larger version (18K): [in a new window]   Fig. 4. (A–D) Pressures when there was siphon-driven flow, and the valve at P4 was closed. Closed triangles show pressures when the jugular limb extension tube was not attached, and closed circles when it was attached. Note that in A, P1–P3 (carotid) pressures were reduced by the extension tube. In B–D, the extension tube had no effect on carotid pressure. In all cases the extension tube reduced jugular tube pressures by the expected 30 mmHg. (E–H) Pressures when there was pump-driven flow of 4 l min–1 through the model. Circles show pressures when the extension tube was attached and triangles when it was not. Open circles and open triangles show pressures with the valve at P4 open. Note that in E and F opening the valve, and thereby removing the effect of the siphon in the rigid jugular tube, resulted in pressures identical to those in tube configurations (G and H) where the jugular tube was collapsible. In G and H the pressures were not affected by a siphon or by the position of the valve, because of the presence of the collapsible jugular tube. B, brain; C, carotid tube; J, jugular tube.

View larger version (14K): [in a new window]   Fig. 5. The effects of constriction of the lowermost `jugular cuff' (R4) region of the jugular tube. Constriction of the `jugular cuff' area of the jugular tube (R4) does not produce typical giraffe jugular pressures.

View larger version (15K): [in a new window]   Fig. 6. The effect of adding brain vascular resistance, or changing flow, on pressures. (A,B) Pressures at all sites when brain (A) or brain and jugular (B) tubes were collapsible and resistance was added to the brain tube (magnitude indicated by R20, R40 etc beside traces). In A and B adding external pressure to the collapsible `brain' tube increased carotid pressures in proportion to the increase in external pressure. Pressures in the jugular tube follow previous findings and were unaffected by external pressure on the brain tube. (C,D) The effect of changes in flow generated by the pump (flow magnitude indicated by legend between panels) on pressures generated in the `carotid' when the brain (C) or brain and jugular (D) tubes were collapsible. Open symbols show pressures when the extension tube was not attached and closed symbols when it was attached. When the jugular tube was rigid (C), increasing the flow increased carotid pressures. When the jugular tube was collapsible (D) increasing flow had no effect on carotid pressures. B, brain; C, carotid tube; J, jugular tube.