AN INTRINSIC POSITIVE END-EXPIRATORY PRESSURE LUNG MODEL, WITH AND WITHOUT FLOW LIMITATION

Objective: To design an intrinsic positive end-expiratory pressure (PE EP) lung model that has the property of air flow limitation. Design: M echanical lung model study of intrinsic PEEP. Setting: Lung models wer e set up in the research laboratory. Interventions: Intrinsic PEEP lun g models were created with and without flow limitation. In the model w ith flow limitation, intrinsic PEEP was created by replacing a portion of the expiratory circuit with a collapsible Penrose tube and by plac ing this portion the circuit under water. The expiratory circuit becam e a part of the respiratory airway, with flow limitation occurring at the Penrose drain. In the model without flow limitation, intrinsic PEE P was generated with a fixed linear resistor, which was inserted in th e expiratory circuit to produce a similar level of intrinsic PEEP. Mul tiple levels of external PEEP, both above and below the initial intrin sic PEEP, were applied. Measurements and Main Results: At each level o f external PEEP, peak airway pressure, plateau airway pressure, isovol ume air flow, internal lung pressure, and intrinsic PEEP were measured . Peak airway pressure, plateau pressure, and internal lung pressure w ere minimally affected if the external PEEP was less than the intrinsi c PEEP in the lung model with flow limitation. Intrinsic PEEP was redu ced 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. Conc lusions: We demonstrated two different models of an intrinsic PEEP lun g model. The interactions between intrinsic PEEP and externally applie d PEEP were different. The lung model with collapsible tube closely si mulated the human respiratory system with flow limitation. This lung m odel may be useful for the future study of intrinsic PEEP and pulmonar y mechanics.