Vascular and airway pressures, and intersititial edema, affect peribronchial fluid pressure

Peribronchial-perivascular fluid pressure (Px(f) was measured relative to pleural pressure in six freshly excised dog lobes. Rapidly equilibrating saline-filled open-end catheters were inserted between lobar bronchus and artery to depths of 3 cm from the hilum. Px(f) was -4 to -8 cmH2O at resting lung volume and became more negative as transpulmonary pressure (Ptp) was increased, and less negative as vascular volume was increased. For example, at constnat Ptp = 30 cmH2O, mean Px(f) rose, respectively, from -35 to -31, -24, -16, and -4 cmH2O, as vascular pressure (Ppa/pv) was increased from -15 to 0, +10, +20, and +30 cmH2O. Lung weight rose steadily at Ppa/pv above 10, reflecting the development of edema. Px(f) had a significant hysteresis with respect to Ptp, being more negative in deflation. As lung edema developed, Px(f) became progressively less negative or slightly positive (even at high Ptp and low Ppa/pv) and hysteresis diminished. Modified wick catheters employed in four additional lobes gave similar results. These data suggest that Px(f) is strongly influenced by bronchovascular-parenchymal interdependence, and that when regions with negative Px(f) absorb fluid the negative pressure may be eliminated.