Abstract
It is well known that beta-adrenergic agonist bronchodilators result in transient decreases in PaO2 levels in spite of bronchodilation. On the other hand, anticholinergic bronchodilators have been shown to have no effects on arterial blood gases. We hypothesized that the bronchodilation might alter oxygen transport from the trachea to alveoli, because the oxygen transport in the airway is governed by convection rather than diffusion. We constructed a 4D finite element lung model in which one subacinus (= the airspace supplied air by one last respiratory bronchiole) and its entire airway was included. Other lung regions were modeled as cubic sets whose side lengths were equal to their air-supplying bronchi. The lung model was moved during two seconds so that the air went into the lung from the tracheal upper open end at a constant flow rate at upright posture. By Solving incompressible Navier-Stokes equation and oxygen diffusion equation simultaneously, oxygen concentration distribution within the airway was computed. The small-airway dilation reduced oxygen concentration by 40% in average. Meanwhile, the large-airway dilation little changed it. This was because the air velocity at periphery was decrease by the small-airway dilatation, and oxygen transport there was performed only by diffusion. These results have indicated that the small-airway dilation itself decreases the arterial blood oxygen level.
