Effect of dehydration on interstitial pressures in the isolated dog lung

We have determined the effect of dehydration on regional lung interstitial pressures. We stopped blood flow in the isolated blood-perfused lobe of dog lung at vascular pressure of ~ 4 cmH₂O. Then we recorded interstitial pressures by micropuncture at alveolar junctions (Pjct), in perimicrovascular adventitia (Padv), and at the hilum (Phil). After base-line measurements, we ventilated the lobes with dry gas to decrease extravascular lung water content by 14 ± 5%. In one group (n = 10), at constant inflation pressure of 7 cmH₂O, Pjct was 0.2 ± 0.8 and Padv was -1.5 ± 0.6 cmH₂O. After dehydration the pressures fell to -5.0 ± 1.0 and -5.3 ± 1.3 cmH₂O, respectively (P < 0.01), and the junction-to-advential gradient (Pjct-Padv) was abolished. In a second group (n = 6) a combination of dehydration and lung expansion with inflation pressure of 15 cmH₂O further decreased Pjct and Padv to -7.3 ± 0.7 and -7.1 ± 0.7 cmH₂O, respectively. Phil followed changes in Padv. Interstitial compliance was 0.6 at the junctions, 0.8 in adventitia, and 0.9 ml · cmH₂O^-1 · 100 g^-1 wet lung at the hilum. We conclude, that perialveolar interstitial pressures may provide an important mechanism for prevention of lung dehydration.