An intrinsic positive end-expiratory pressure lung model, with and without flow limitation

Objective To design an intrinsic positive end-expiratory pressure (PEEP) lung model that has the property of air flow limitation. Design Mechanlcal lung model study of intrinsic PEEP. Setting Lung models were set up in the research laboratory. Interventions Intrinsic PEEP lung models were created with and without flow limitation. In the model with flow limitation, intrinsic PEEP was created by replacing a portion of the expiratory circuit with a collapsible Penrose tube and by placing this portion the circuit under water. The expiratory circuit became a part of the respiratory airway, with flow limitation occurring at the Penrose drain. In the model without flow limitation, intrinsic PEEP was generated with a fixed linear resistor, which was inserted in the expiratory circuit to produce a similar level of intrinsic PEEP. Multiple levels of external PEEP, both above and below the initial intrinsic PEEP, were applied. Measurements and Main Results At each level of external PEEP, peak airway pressure, plateau airway pressure, isovolume air flow, internal lung pressure, and intrinsic PEEP were measured. Peak airway pressure, plateau pressure, and internal lung pressure were minimally affected if the external PEEP was less than the intrinsic PEEP in the lung model with flow limitation. Intrinsic PEEP was reduced with external PEEP. However, if intrinsic PEEP was induced without dynamic airway closure or flow limitation, any level of external PEEP caused an immediate increase in peak airway pressure, plateau airway pressure, and internal lung pressure and a decrease in isovolume flow. External PEEP has little effect on the levels of intrinsic PEEP. Conclusions We demonstrated two different models of an intrinsic PEEP lung model. The interactions between intrinsic PEEP and externally applied PEEP were different. The lung model with collapsible tube closely simulated the human respiratory system with flow limitation. This lung model may be useful for the future study of intrinsic PEEP and pulmonary mechanics. (Crit Care Med 1996; 24:1261-1265)