Blood Flow Pulsatility Effects upon Oxygen Transfer in Artificial Lungs

This report discusses theoretical effects of blood flow pulsatility upon the rate of oxygen transfer in artificial lungs, demonstrates the effects with in vitro tests upon commercial oxygenators, and applies the theory to these oxygenators and to a thoracic artificial lung. Steady flow gas transfer theory is applied to pulsatile flow by using the instantaneous value of flow rate at each instant of time, that is, quasi-steady gas transfer. The theory suggests that the local rate of oxygen transfer for a given device and blood composition is proportional to the flow rate to a power less than unity and to the hemoglobin saturation level. It predicts, for some cases, overall reduced rates of gas transfer for pulsatile flow relative to those at steady flow for the same mean blood flow rates. In vitro bovine blood tests, using pediatric oxygenators, a pulsatile pump, and an adjustable compliance chamber, indicate a significant average 10% reduction of oxygen transfer for pulsatile flow relative to steady flow. The application of the theory to the oxygenators predicts gas transfer values that are in agreement with those measured during the experiments. The results have implications in the design of implantable thoracic artificial lungs, which should include a compliant section to dampen the cardiac pulse. A relatively small compliance (0.2 mi/mm Hg) at the thoracic artificial lung inlet is sufficient to obtain approximately 95% of steady flow oxygen transfer.