Regional compliance and bronchial pressure-diameter relationships in excised pig lungs

We estimated the magnitude of parenchymal interdependence in excised pig lungs by measuring small airway diameter during homogeneous and nonhomogeneous lung inflation, by comparing the ratio of the specific compliance of the lung (Cl) to the specific compliance of a single lung region (Cs) and by using a continuum mechanics analysis to estimate the pressure at the interface between a single lung region and the surrounding lung. We found that the diameter of airways in a single lung region increased when the lung was held at a transpulmonary pressure (Ptp) of 5, 10 or 15 cmH2O and pressure in the region was increased by up to Ptp + 15 cmH2O, indicating that the surrounding lung offered little resistance to expansion of the lung region. The ratio of Cl to Cs averaged 1.22 (n = 5 lungs), indicating that the parenchyma surrounding the lung region caused a small reduction in its distensibility. When the lung was held at a Ptp of 5 cmH2O, pressure at the interface was estimated to be 1.1, 0.8 and -1.9 cmH2O when pressure in the single lung region was 15, 10 and O cmH2O, respectively. The relatively small change in boundary pressure from pleural pressure as the region was inflated or deflated indicated that the mechanical interaction between adjacent lung regions was small. Taken together, these results confirm the prediction of a small interdependence effect as determined by measurements of the distensibility and distortability of the pulmonary parenchyma.