[Effects of venous segment pressure on the critical closure pressure, in the isolated lung lobe from dogs in situ].

In an isolated in situ canine left lower lobe preparation we studied the influence of the distal vascular compartment or venous pressure (PV) on the pressure of arterial vascular segment at zero flow or minimal critical closing pressure (MCCP), while alveolar pressure was held constant and below MCCP. The MCCP-PV curve showed an independent segment when PV was less than 8 mmHg. Above this value (that we define as PV), an slope of 1.08 was found. Our findings indicate that MCCP is not MCCP if PV greater than 8 mmHg (it is MCCP). Because MCCP is higher than alveolar pressure, MCCP must be the back pressure for flow. This finding is not in disagreement with the new concept regarding that MCCP is the back pressure for flow and not alveolar pressure in West's zone II condition.