Effect of increased static lung recoil on ventilation distribution in excised human lungs

The contour of a modified Fowler single-breath nitrogen washout was determined in 15 postmortem human lungs before and after static lung recoil had been increased by ventilation. Before ventilation, expiratory nitrogen versus volume curves exhibited the 4 phases similar to those seen in intact human lungs. The tests were repeated after ventilation with humidified air at room temperature for 3 hours at pleural pressures between -20 and +10 cm H2O at 15 breaths per min. After ventilation, the slope of the alveolar plateau (Phase III) decreased (P less than 0.01); the volume of Phase IV increased (P less than 0.01); and the closing capacity (Phase IV plus minimal volume) decreased (P less than 0.01). The data suggest that in the human lung the onset of Phase IV is not solely dependent on a pleural pressure gradient and that after ventilation, when static lung recoil is increased, the distribution of inspired gas in the excised human lung is more uniform, and at least some lung units empty more completely before zero transpulmonary pressure is reached.