A closed-loop model of human gas exchange

We have developed a closed-loop gas exchange model of the human. In our previous model of the human cardiopulmonary system, only gas transport at lungs were included, and the inlet blood O₂ and CO₂ concentrations to the lungs were fixed at constant values. We now add a description of the tissue gas exchanger, and couple these gas exchangers via the circulatory loop in our human cardiopulmonary model. Thus, gas transport in the lungs and at the blood-tissue interface interact as part of a closed-loop system, where the output of one gas exchanger provides the input to the other. The model predicts physiological variables that agree well with typically observed data in human, and also the simulated response to induced asphyxia. The study suggests an important role for transport delay in maintaining the arterial O₂ tension and resisting hypercapnia during asphyxia. The simulation results also show the existence of diffusion limitation of O₂ in tissue.