Static mechanics of excised whole lung: theoretical framework and experimental studies

A theoretical framework is presented in which to view models of static pulmonary mechanics. To test common simplifying assumptions of these models, we performed a set of experiments using normal lungs excised from dogs. Transpulmonary pressure (Ptp) and lung volume (VL) were measured for air-filled lungs in air and saline-filled lungs in saline during stepwise-static deflations at different vascular volumes and temperatures. Simultaneously, we measured displacements between points on the lung surface. Changes in vascular volume shift the location but not the shape of the Ptp-VL relationship. As long as the vascular pressure is in the normal range, changes in the volume (and weight) of the perfusate do not significantly stiffen the parenchyma. Furthermore, Ptp-VL data obtained between 16 degrees C and 40 degrees C were superimposable, indicating that parenchymal mechanical properties evaluated at room temperature are valid at body temperature. Finally, the common assumptions of uniform deflation, homogeneity, and isotropy of bulk lung tissue appear consistent with the relationship between surface displacement and volume changes.