Abstract
Cough is a protective respiratory reflex used to clear respiratory airway mucus. For patients with cough weakness, such as chronic obstructive pulmonary disease, neuromuscular weakness disease and other respiratory diseases, assisted coughing techniques are essential to help them clear mucus. In this study, the Eulerian wall film model was applied to simulate the coughing clearance process through a computational fluid dynamics methodology. Airway generation 0 to generation 2 based on realistic geometry is considered in this study. To quantify cough effectiveness, cough efficiency was calculated. Moreover, simulations of four different coughing techniques applied for chronic obstructive pulmonary disease and neuromuscular weakness disease were conducted. The influences of mucus film thickness and mucus viscosity on cough efficiency were analyzed. From the simulation results, we found that with increasing mucus film thickness and decreasing mucus viscosity, cough efficiency improved accordingly. Assisted coughing technologies have little influence on the mucus clearance of chronic obstructive pulmonary disease models. Finally, it was observed that the cough efficiency of the mechanical insufflation-exsufflation technique (MIE) is more than 40 times the value of an unassisted coughing technique, which indicates that the MIE technology has a great effect on airway mucus clearance for neuromuscular weakness disease models.
Highlights
As a protective respiratory reflex, cough clears mucus from the respiratory tract and keeps it clean and unobstructed
The current assisted coughing techniques recommended for airway clearance mainly include manually assisted coughing (MA)[20]; mechanical insufflation (MI), which produces a cough after the inspiration supplied by a ventilator[21]; mechanical exsufflation (ME), which presents the negative pressure at the end of inspiration[22]; and mechanical insufflation/exsufflation (MIE), which promotes maximal lung inflation by positive pressure followed by a sudden switch to negative pressure to create a high airflow[23]
The velocities are made nondimensional with the outflow bulk velocity
Summary
As a protective respiratory reflex, cough clears mucus from the respiratory tract and keeps it clean and unobstructed. The coughing process can be characterized by three key parameters: cough expired volume (CEV), cough peak flow rate (CPFR) and peak velocity time (PVT)[4,5,6,7,8]. These parameters provide good insight into the flow behavior in the coughing process. The high airflow velocity creates a high shear stress that shears secretions and foreign matter off the bronchial wall and propels them toward the larger airways and trachea. Because of airflow obstruction, patients with chronic obstructive pulmonary disease (COPD) may present with weak cough and airway mucus deposition. The current assisted coughing techniques recommended for airway clearance mainly include manually assisted coughing (MA)[20]; mechanical insufflation (MI), which produces a cough after the inspiration supplied by a ventilator[21]; mechanical exsufflation (ME), which presents the negative pressure at the end of inspiration[22]; and mechanical insufflation/exsufflation (MIE), which promotes maximal lung inflation by positive pressure followed by a sudden switch to negative pressure to create a high airflow[23]
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