N95 respirator mask breathing leads to excessive carbon dioxide inhalation and reduced heat transfer in a human nasal cavity

Hana Salati; Mehrdad Khamooshi; Sara Vahaji; Farid C Christo; David F Fletcher; Kiao Inthavong

doi:10.1063/5.0061574

N95 respirator mask breathing leads to excessive carbon dioxide inhalation and reduced heat transfer in a human nasal cavity

Phys Fluids (1994). 2021 Aug;33(8):081913. doi: 10.1063/5.0061574. Epub 2021 Aug 23.

Authors

Hana Salati, Mehrdad Khamooshi¹, Sara Vahaji², Farid C Christo², David F Fletcher³, Kiao Inthavong¹

Affiliations

¹ Mechanical and Automotive Engineering, School of Engineering, RMIT University, Bundoora, Australia.
² School of Engineering, Faculty of Science Engineering and Built Environment, Deakin University, Victoria, Australia.
³ School of Chemical and Biomolecular Engineering, The University of Sydney, NSW 2006 Australia.

Abstract

Face masks and respirators are used to filter inhaled air, which may contain airborne droplets and high particulate matter (PM) concentrations. The respirators act as a barrier to the inhaled and exhaled air, which may change the nasal airflow characteristics and air-conditioning function of the nose. This study aims to investigate the nasal airflow dynamics during respiration with and without an N95 respirator driven by airflow through the nasal cavity to assess the effect of the respirator on breathing conditions during respiration. To achieve the objective of this study, transient computational fluid dynamics simulations have been utilized. The nasal geometry was reconstructed from high-resolution Computed Tomography scans of a healthy 25-year-old female subject. The species transport method was used to analyze the airflow, temperature, carbon dioxide (CO₂), moisture content (H₂O), and temperature distribution within the nasal cavity with and without an N95 respirator during eight consecutive respiration cycles with a tidal volume of 500 ml. The results demonstrated that a respirator caused excessive CO₂ inhalation by approximately $7 \times$ greater per breath compared with normal breathing. Furthermore, heat and mass transfer in the nasal cavity was reduced, which influences the perception of nasal patency. It is suggested that wearers of high-efficiency masks that have minimal porosity and low air exchange for CO₂ regulation should consider the amount of time they wear the mask.