Validation of a Model for Flow-Dependent Carbon Dioxide Exchange in Artificial Lungs

Abstract: The exchange rate of CO₂ in artificial lungs depends on the sweep gas flow rate. Control of the amount of CO₂ removed by an artificial lung requires quantitative knowledge of the flow dependence. A simple model of the dependence of CO₂ exchange on sweep gas flow rate in artificial lungs has been previously presented (1). For a given partial pressure of CO₂ in the blood phase, sweep gas flow rate, and CO₂ exchange rate, the model indicates how close the CO₂ exchange rate is to the maximum level attainable by the artificial lung. The focus of this study was to validate the model experimentally by testing 2 commercial artificial lungs in an in vitro test loop. The CO₂ exchange rate for each artificial lung was measured over a range of sweep gas flow rates. Linear regression was used to fit the data to the model and estimate the maximum possible CO₂ exchange rate and the average water-side P co₂ ( Pco₂^w). The difference between the measured and regressed values of Pco₂^w was used as an indicator of the ability of the model to quantitatively predict the dependence of CO₂ exchange on gas flow rate. This difference was less than 5% for each experiment, indicating that the model can be used to guide control of CO₂ exchange rates in artificial lungs.