[Gaseous dispersion in the central airways of the human lung. In vivo study]

In order to estimate the contribution of either laminar or turbulent 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 takes into account, along with the summed cross-section of Weibel lung model [31], both axial convection and longitudinal dispersion of helium and sulphur hexafluoride in air. The simulations were carried out by incorporating two dispersion coefficients corresponding to laminar and turbulent flow into the mathematical model. The experiments were performed on five normal subjects by injection of 10 ml bolus of helium and sulphur hexafluoride into the later part of the inspired airstream in such a way that the whole bolus entered the inspiratory flow and was recovered during the following expiration. When the experiment is simulated using the laminar dispersion coefficient, no concordance could be seen between computed and experimental data; however, there is a good concordance when the simulation is performed with the turbulent dispersion coefficient. It is concluded that Taylor laminar dispersion [24] cannot play a significant role in the human airways; however, it seems that convective gas mixing with turbulent dispersion [21] can account for most gas transport during spontaneous ventilation.