Giraffes, Siphons, and Starling Resistors: Cerebral Perfusion Pressure Revisited
Highlights
- In the case of Zone 2 conditions (Fig. 1), the alveolar pressure (PA) is greater than the pulmonary venous pressure (PV). As originally described by West (4) blood flow through this zone is responsive to the pressure gradient between arterial pressure (Pa) and PA, but is completely independent of the far downstream venous pressure PV. (View Highlight)
- A Starling resistor is any collapsible conduit surrounded in its middle section by an external pressure that is higher than the outlet pressure (View Highlight)
- Critical closing pressure is the exact upstream pressure (usually greater than zero), where vessels begin to collapse from their own smooth muscle tone and blood flow falls to zero. It is also called zero flow pressure. (View Highlight)
- The vascular waterfall concept assumes that a collapsible vessel has to have an internal pressure equal to the external pressure applied to it in order to remain open. It further assumes that an equilibrium is reached where, as flow continues, pressure within the collapsible element falls until the vessel tends to collapse, at which point internal pressure again builds up, opening the vessel for continued flow (View Highlight)
- The chief difference between a vascular waterfall and a Starling resistor is that, in the waterfall, it is active vessel wall tone rather than external pressure that causes a tendency to collapse (View Highlight)