Meniscus formation in airways of excised rat lungs

The object of this study was to determine the transpulmonary pressure at which menisci form in the airways of excised rat lungs. The necessary geometric requirements for meniscus formation are normally met in the airways, but a meniscus is presumably prevented from forming at large lung volumes because too little fluid is present. At lower lung volumes a meniscus could form easier since airway caliber is reduced and less fluid is required. A series of pressure-volume curves were recorded for lungs in which meniscus formation was inhibited by increasing the end expiratory pressure. Assuming the number of airways containing at least one meniscus was proportional to the amount of gas trapped in the excised rat lung, it was found that the menisci were formed in 68% of the airways between positive transpulmonary pressures of 1.4 and 3.0 cm H2O during deflation.