Finite element simulation of gas transport in proximal respiratory airways: Comparison with experimental data

In order to study gaseous dispersion in the central airways during spontaneous breathing, the results of the computer simulation of a mathematical model were compared with those of an appropriate in vivo test performed on normal subjects. The model is governed by a gas transport equation—with a convection and dispersion term—solved for Weibel geometry by a finite element method. The numerical computation for this equation was tested by the analytical solution in a particular geometric situation. For each trial (injection of a 3-ml argon bolus in the latter part of a quiet inspiration), a simulation was performed, using the inspiratory bolus as the nonzero limit condition (input signal); the value of the mixing coefficient D was optimized so as to fit the experimental data. Whatever the value of D , no similarity could be found when the bolus was injected in front of the lips. In one volunteer the injection was performed through an endotracheal tube: computer and experimental results are much closer. It is concluded that (1) the upper airways play a specific role in gas transport (2) the model should be improved by allowing variations of D according to the depth in the airways and the gas velocity.