Characterization of the laryngeal jet using phase Doppler interferometry.

Abstract

The purpose of this study was to characterize the effects of the laryngeal jet on inhalation air flows in the trachea, and to extend these ideas to further an understanding of aerosol deposition in this region. Phase Doppler Interferometry was used to characterize axial velocity and turbulence intensity contours in the tracheal section of a cadaver-based larynx-trachea model. An array of 30 measurements was made at each of 6 downstream planes within the tracheal portion of the model (immediately downstream of the larynx, and at 0.5, 1, 2, 3, and 4 diameters further downstream). The flow was characterized for steady state flow at three Reynolds numbers (1250, 1700, and 2800). The Re = 1250 case approximates the inhalation of a 6-year-old child. Reverse flows with significant velocities were noted in the anterior trachea within one diameter downstream of the larynx, for all three flow cases. The cross sectional area of the reverse flow regions was larger for the lower Reynolds number cases. These reverse flows are a consequence of the nearly triangular shape of the lumen between the vocal folds in the larynx and constitute a potential deposition mechanism. High levels of axial turbulence intensity were noted near the anterior/left tracheal walls within one diameter downstream of the larynx. This indicates the potential for deposition due to turbulence in this region. Turbulence levels were still significant after four downstream diameters, indicating the potential for turbulent deposition at positions further downstream, including the bronchial tree where passage diameters are smaller. Contrary to expectations, turbulence levels were approximately 20% higher for the Re = 1250 case compared to the Re = 2800 at the furthest downstream locations (with 99% confidence). This is likely due to the complex nature of the confined jet flow.