The Science Journal of the American Association for Respiratory Care

1998 OPEN FORUM Abstracts

A SIMPLE LUNG MODEL THAT MIMICS DYNAMIC AIRWAY COLLAPSE, AND DEMONSTRATES UPPER AND LOWER INFLECTION POINTS ON A PRESSURE VOLUME CURVE.

Robert McConnell, RRT, Dennis Yetsko, RRT, Michael Gentile, RRT, Neil MacIntyre, MD, Duke University Medical Center, Durham, NC.

The use of static or slow flow pressure volume (PV) curves to evaluate critical opening pressure (lower inflection point) and maximal lung inflation (upper inflection point) has been well documented. The ability to easily demonstrate this phenomenon for the purpose of teaching and discussing methods of treatment has required assembly of inconvenient, cumbersome, and relatively impractical models. We devised a simple model that is easy to use, and can be assembled using devices and materials common to most respiratory care departments. The equipment needed: hard plastic canister from an HCH/HME with luer-lock gas sample port (humidification and filter media removed), large Penrose drain tube, variety of adapters (15mm, 22mm, etc.), and a dual chamber mechanical lung. The Penrose tubing is cut and placed inside the canister with the ends stretched over the outer connections. The assembled device functions to represent the dynamic closure and collapse of airways. Pressurizing the canister (using a syringe and stopcock to the gas sample port) at various levels, collapses the tubing, requiring airway pressure to open the tubing during inspiration. Graphically this will be represented as the lower inflection point of a PV curve (see figure).

(See original for figure)

Using adapters the device is placed between the circuit wye of the ventilator and one chamber of the mechanical lung (main chamber). The other chamber (dependent lung) should be outfitted with a tie bar to facilitate lifting when the main chamber is inflated. The maximal lung inflation or high cost of pressure for volume change is demonstrated by splinting open the dependent chamber of the lung to some volume thereby creating a point at which the pressure would rise sharply as the main chamber of the lung is forced to lift the dependent chamber. This point is graphically represented as the upper inflection point of a PV curve (see figure). Once connected to the mechanical ventilator, pressure volume curves can be traced and measurement of the inflection points can be made (figure from COSMO-Plus, Novametrix, Wallingford, CT). This same model could be utilized with a super syringe for static pressure volume curve demonstrations. CONCLUSION: This model can be an important demonstration of the effect of PEEP in lung recruitment, and the identification of maximal lung volume during mechanical ventilation.

The 44th International Respiratory Congress Abstracts-On-DiskĀ®, November 7 - 10, 1998, Atlanta, Georgia.

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