Lung tissue resistance measured in saline-filled guinea pig lungs by micropuncture

Lung tissue resistance (Rti) measured in air-filled guinea pig lungs by the alveolar capsule technique was a large part of total lung resistance (Rl), and we wondered whether similar results applied to saline-filled lungs. We used the micropuncture method to measure alveolar pressure (Palv) in saline-filled lungs of 21 guinea pigs. Palv and airway opening pressure (Pao) were measured before and after a sudden interruption of flow during an inflation or deflation maneuver. On stopping flow, there was an immediate large change in Pao followed by a smaller slower change in Pao. Palv was nearly constant immediately after flow interruption but followed the slower change in Pao. The initial change in Pao on flow interruption was interpreted as the resistive pressure loss in the airways. The small change in Pao and Palv was interpreted as the pressure loss caused by tissue stress adaptation. Airway resistance (R(aw)) and Rti were obtained by dividing the pressure losses by the flow before the interruption. Rl was the sum of R(aw) and Rti. The calcium blocker nifedipine reduced both R(aw) and Rti and abolished the difference in Rti between inflation and deflation. Values of Rti were 10-29% of Rl. However, with correction for viscosity, Rti predicted in air-filled lungs would dominate Rl.