The effects of respiratory support on blood gases were investigated in computer models of O2 and CO2 gas transports in the membrane oxygenator—patient system. The O2 and CO2 gas exchange model for a one-squaremeter Landé-Edwards membrane oxygenator was constructed through the experiments and the theoretical analyses of the transfer of O2 and CO2. The distressed lung was modeled by considering decreased alveolar ventilation, ventilation—perfusion inequality and increased anatomical shunt. Simulation studies at a steady state were performed in both veno-venous and veno-arterial perfusions.
By the calculations which indicate the degree of improvement in arterial O2 and CO2 tensions followed by increasing a bypass flow rate, the followings were predicted. 1) The improvement of arterial blood is considerably dependent on the factors of respiratory insufficiency. The expected improvement is the greatest in decreased alveolar ventilation, medium in ventilation—perfusion inequality and relatively less in direct shunting, when other conditions are identical. 2) In the range of low bypass flows, no significant differences in the improvement are seen among the perfusion methods. In the range of high bypass flows, however, veno-arterial perfusion reduces the assisting effect because the maximum improvement is attainable at an appropriate bypass flow rate. On the other hand, veno-venous perfusion increases the assisting effect with increasing a bypass flow rate. 3) In CO2 tension the improvement is obtained at a relatively low flow rate, compared with in O2 tension. But, the additional improvement with high bypass flow is not to be expected even in veno-venous perfusion.
The experiments on dogs with decreased alveolar ventilation exhibited the similar effects to the simulation. The method of perfusion, the number or the size of oxygenators and the rate of bypass flow could be determined by this quantitative analysis.
