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.