Microfluidic investigation of alveolar Pendelluft via tunable compliance sacs and time-resolved micro particle image velocimetry

To investigate the Pendelluft effect, a pathological phenomenon caused by lung time-constant inhomogeneity, this study provides a simple yet accurate experimental framework for fabricating microscale respiratory bifurcations using simple air chambers to model alveolar compliance with mismatched compliance values. An experimental model of seven respiratory branches with one inlet and four outlets within a three-dimensional (3D) printed microchannel is constructed, where the air chambers are connected to each outlet of the model. Time-resolved high-fidelity micro particle image velocimetry (μPIV) experiments are performed using fluorescent particles to visualize and measure the Pendelluft effect in a respiratory cycle with significant compliance mismatch. Computational fluid dynamics simulations are also used to assess the accuracy of the specified boundary conditions and to validate the methodology. A close agreement between the experiments and the numerical flow field is observed, including small flow features such as half-saddles, time-dependent velocity profiles, and flow fields. Due to a significant impedance mismatch between the sub-branches with subtended acini of 50% compliance difference, a phase shift of around 16° was observed from experimental results. The phase shift is attenuated in the upper generation to a value of around 7°. A distinct transient pure Pendelluft regime with a stagnant region is identified in the μPIV results during the inspiration and expiration phases. These findings demonstrate that the proposed air-chamber approach provides a predictable and physiologically relevant experimental platform for quantifying complex respiratory flows associated with heterogeneous lung mechanics that can be implemented in various lung-on-the-chip micro-devices.