Influence of glottic aperture on the tracheal flow.

The extra-thoracic mouth-throat area has a major influence on the aerosol delivery to the proximal or peripheral intra-thoracic airways. To characterize the particle deposition in this area, it is important to investigate first the flow structures in this crucial--in relation to the aerosol deposition--region. The glottis, which is delimited by the vocal cords and therefore has the narrowest passage, generates a laryngeal jet and a reverse flow downstream the glottis. It is generally assumed that the glottis has different shapes and cross-sectional areas at different moments during the respiratory cycle and also depends on the average inspiratory flow rate. Therefore, the influence of a circular glottal aperture, with a cross-sectional area of 90 mm2 and an elliptical and triangular shape, both with an area of 45 mm2, on the flow is investigated. However, the area of the circular aperture is twice as big as the area of the elliptical one, it has almost no influence on the flow structures. On the other hand, the triangular glottal aperture shifts the laryngeal jet in the direction of the posterior wall, and generates two pairs of counter rotating secondary vortices downstream the glottis, where the circular and elliptical only aperture generates one pair of vortices. The difference in pressure drop is more dominated by the cross-sectional area than by the shape of the glottis. This suggests the need for rendering geometry of future upper airway models even more realistic as the appropriate three-dimensional (3D) medical imaging techniques are becoming available.