Abstract
Several factors affecting the volume of trapped gas (VTG) were examined in excised rat lungs. After degassing, five successive cycles were made at 30°C in plethysmograph between pre-set inflation and deflation pressure limits at a controlled flow rate (V). The transpulmonary pressure and lung volume were recorded directly on an X-Y plotter. When V varied between 1ml/min to 243ml/min, VTG was found to be most dependent on the inflow rate, especially at V below 9ml/min. However, VTG also depends critically on low end-expiratory pressure (EEP). Minimum trapping occurs when EEP is greater than 4cmH2O. It appears that trapping depends on airway menisci formed at low EEP, and that the production of obstructing foam depends on advancing menisci into terminal units by a very slow flow rate.
