DPIV Measurements of Dynamic Flow Patterns in a Realistic Model of the Lung Airways Down to the 6th Generation

The objective of the study is a more detailed analysis of lung ventila tion under normal breathing conditions and for artificial, respirator-assisted ventilation. Therefore a realistic 3D model of the lung down to the 6 generation was generated to investigate the oscillatory flow through the branching network by DPIV. A transparent model made of silicone is used in combination with a refractive index matching fluid (water/glycerin). The Measurements were carried out using hydrogen bubbles as tracer particles. The mass flow rate and the frequency were adapted to the characteristic flow parameters of the air flow in the human lung keeping the Reynoldsand Womersley-number constant. A first comparison of the results for the inspiration and expiration phase demonstrates the different nature of the flow. During inspiration one can see larger flow separation regions at the outer walls of the bifurcating channels which sometimes extend downstream to the next bifurcation. In contrast, the flow at expiration does not separate at all and shows the typical jet-like profile at the exit of the trachea. The complete cycle of inspiration and expiration suggests that due to the transformation of the velocity profiles and the generated separation regions a net mass flow is created into the model along the centerline and the inner walls of the bifurcations. This is compensated with a net mass outflow to the trachea along the outer walls of the branches along the separation regions which are washed upstream during expiration. At higher breathing frequencies this effect is enhanced which may help to remove deposited particles in the lung network.