Respiratory airflow model clarifies how coughing clears mucus

Coughing is an important and natural respiratory reflex that clears mucus. Without effective coughing, continual mucus deposition can promote bacterial reproduction and pulmonary infection and seriously impact patients with lung conditions like chronic obstructive pulmonary disease (COPD).

Ren et al. reconstructed 3D human respiratory airways using computerized tomography images to analyze the airflow-mucus interaction phenomenon in time and space. The study was the first to consider both the lower and upper airways.

The team tested different mucus viscosities, as the parameter can reach 10 to 100 times that of normal conditions in COPD and cystic fibrosis patients. They examined three cough parameters and their effect on dynamics and cough efficiency, the ratio of mucus mass after to before the cough.

The expired volume and peak flow rate quantify the total expired air volume and the maximum airflow rate in a single cough process. The peak velocity time measures the beginning of the cough to its peak airflow rate.

Increasing the cough peak flow rate had no noticeable effect on mucus clearance under normal and low mucus viscosity but did effectively improve clearance under high mucus viscosity. The cough expired volume had a positive effect on clearing mucus regardless of the viscosity and thickness.

“Unlike the previous understanding that improving the peak cough flow rate could improve mucus clearance, this study proved that the cough expired volume has a more apparent positive effect on clearing mucus,” said author Shuai Ren.

While these results were obtained from numerical simulations, the authors plan to validate their findings with experiments. Their goal is to develop improved devices to assist patients with effective coughing.

Source: “Influence of cough airflow characteristics on respiratory mucus clearance,” by Shuai Ren, Maolin Cai, Yan Shi, Zujin Luo, and Tao Wang, Physics of Fluids (2022). The article can be accessed at https://doi.org/10.1063/5.0088100 .

This paper is part of the Flow and the Virus Collection, learn more here .