Oral configuration-dependent variability of the metrics of exhaled respiratory droplets during a consecutive coughing event.

Background And Objective: Coughing events are eruptive sources of virus-laden droplets/droplet nuclei. These increase the risk of infection in susceptible individuals during airborne transmission. The oral cavity functions as an exit route for exhaled droplets. Thus, its configuration contributes significantly to the metrics of exhaled droplets.

Methods: In this study, two realistic numerical models were developed: the respiratory system from the throat to the second bifurcation and the oral cavity with different anatomical structures. A coupling of Eulerian Wall Film (EWF) - Discrete Phase Model (DPM) was employed to numerically describe the generation, absorption and exhalation properties. In addition, two sequential coughing episodes were considered with variegated profiles in the second cough.

Results: As a result, the enlargement of the oral cavity caused considerable alterations in the original spatial distribution and total number concentration of exhaled droplets: these were reduced by approximately 30 %. Considering the consecutive second cough, maintaining or decreasing the flow rates resulted in a decrease in the total quantity of exhalation droplets by 25-90 %. The variations in the oral structure or coughing flow profile also reallocated the local spatial and proportional distribution of exhaled droplet. The expelled droplets/droplet nuclei's size remained approximately 0.25-20 μm range with varied development trends even though the peak concentration reserved unchanged at approximately 5 μm.

Conclusions: This study is a substantial work emphasizing the dependent variability of oral geometry and coughing physiology related to the properties of exhaled droplets. It emphasizes the uncertainties in the input parameters required for indoor transmission risk studies related to intersubject variability.