Design, characterization and application of a coughing simulator for removal of visco-elastic mucus

Cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) patients usually have overly viscous mucus, which provokes repetitive coughing and increase the risk of lung infection. Effective clearance of mucus depends on the shear stress of cough airflow working on the mucus-air interface and overcoming the yield stress of the visco-elastic mucus. Clinical observation showed that air bubbles are induced in mucus during coughing, yet the effects of bubble formation on the mucus removal process remains unclear.

In this study, we designed a benchtop human-cough stimulator to investigate the multi-phase flow dynamics during coughing. A pressurized tank supplies airflows at desired static pressures, which then passes through a transparent sealed chamber with dimensions matching human trachea. To simulate the dynamic pressure, two proportional sinusoidal valves are installed upstream and downstream of the chamber to coordinately modulate the dynamic pressure inside the chamber, superimposing short and high-velocity burst to reproduce cough procedure. Two pressure sensors measuring the static and stagnation pressure transmit real time pressure and velocity data to Ardiuno board. The transparent chamber allows application of high-speed imaging and particle image-velocimetry measurement to capture the morphology and flow dynamics of mucus liquid under controlled conditions.

The preliminary calibration results demonstrate that the simulator offers a reliable platform for studying the complex multi-phase unsteady flows during coughing by reproducing airflow pressure and flow rate matching physiological condition. In the next step, the bubble formation dynamics in viscoelastic fluid will be investigated.