Lung recoil during rapid vital capacity expirations simulated by gas compression

Excised dog lobes were inflated to a transpulmonary pressure (PL) of about 30 cmH2O, and their airways were occluded. Then they were rapidly compressed to a volume where PL was about zero, simulating forced expiratory maneuvers. Since there was no airflow during the compression, PL was a direct measure of lung recoil. Lung volume (VL) was calculated from absolute airway pressure using Boyle's law. At ambient temperature, lung recoil pressure during compressive maneuvers simulating forced vital capacity expirations (Pdyn) was less than that during quasi-static (30 s) compressions (Pst). Typically the dynamic component (i.e., Pst--Pdyn) decreased from about 2 cmH2O near total lung capacity to no difference at the end of the compression. Cooling the lobes to 15 degrees C increased Pst-Pdyn, and warming the lobes to 37 degrees C reduced Pst-Pdyn almost to zero. We suggest that the driving force of lung recoil during expirations is adequately modeled by the quasi-static VL/PL relationship, though a small correction should be made for excised lungs at room temperature.