Does blood flow pulsatility affect oxygen transfer in artificial lungs?

Whether pulsatile blood flow affects O₂ transfer rate in artificial lungs is controversial. Applying steady flow theory to pulsatile flow using the instantaneous value of flow rate at each time (i.e., quasi-steady transfer) predicts reduced rates of gas transfer, as much as 20 to 30%, for pulsatile flow relative to those at steady flow for the same mean blood flow rates. The amount of the reduction depends on the pulse height. In vitro bovine blood tests, using pediatric oxygenators, a Harvard pulsatile pump, and an adjustable compliance chamber, were used to measure any pulsatility effects on oxygen transfer rates. Three average flow rates were used, each with four values of compliance, ranging from 0 to 2 ml/mmHg and producing pulse heights relative to mean flow rates 4.7 to 0.1. Results indicate no significant differences at low flow rates where the devices are fully saturating the hemoglobin for all pulse heights. If the flow rate is high enough such that the hemoglobin is not fully saturated at the outlet, however, blood flow pulsatility resulted in reduced O₂ transfer rates, as much as 20% in these experiments; the higher the pulse height, the lower the O₂ transfer rate. These results have important implications in the design of implantable thoracic artificial lungs.