Effect of alveolar and pleural pressures on interstitial pressures in isolated dog lungs

We report the first direct measurements of perialveolar interstitial pressures in lungs inflated with negative pleural pressure. In eight experiments, we varied surrounding (pleural) pressure in a dog lung lobe to maintain constant inflation with either positive alveolar and ambient atmospheric pleural pressures (positive inflation) or ambient atmospheric alveolar and negative pleural pressures (negative inflation). Throughout, vascular pressure was ~4 cmH₂O above pleural pressure. By the micropuncture servo-null technique we recorded interstitial pressures at alveolar junctions (Pjct) and in the perimicrovascular adventitia (Padv). At transpulmonary pressure of 7 cmH₂O (n = 4), the difference of Pjct and Padv from pleural pressure of 0.9 ± 0.4 and - 1.1 ± 0.2 cmH₂O, respectively, during positive inflation did not significantly change (P < 0.05) after negative inflation. After increase of transpulmonary pressure from 7 to 15 cmH₂O (n = 4), the decrease of Pjct by 3.3 ± 0.3 cmH₂O and Padv by 2.0 ± 0.4 cmH₂O during positive inflation did not change during negative inflation. The Pjct-Padv gradient was not affected by the mode of inflation. Our measurements indicate that, in lung, when all pressures are referred to pleural or alveolar pressure, the mode of inflation does not affect perialveolar interstitial pressures.