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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.
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