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

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 (CO 2 ), moisture content (H 2 O), 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 CO 2 inhalation by approximately 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 CO 2 regulation should consider the amount of time they wear the mask.

Possible toxicity of chronic carbon dioxide exposure associated with mask use, particularly in pregnant women, children and adolescents -a scoping review

“…Those elevated carbon dioxide levels of inhaled air, particularly under N95 masks, have also been found in physiologic relevant short-time modeling studies. This confirms a constant increase leading to an averaged 1% inhaled CO 2 per breath during simulations of eight breathing cycles in 33.65 seconds [21] (see Figure 8 of mentioned publication with animation of CO 2 distribution with and without a respirator). Another modeling study shows that wearing N95 masks results in carbon dioxide accumulation, the volume fraction of CO 2 reaches 1.2% after 7 breathing cycles and is then maintained at 3.04% on average.…”

“…Secondly, the CO 2 sampling point chosen by Geiss above the tip of the nose on the bridge of the nose is suboptimal for mask measurements. This is because it is not close enough to the openings involved in breathing, which are shielded from the rest of the dead space of the mask by the protruding tip of the nose (see figure 1A in Geiss publication to illustrate the questionable placement of sensor [26] and compare it to the gas distribution video in Salati [21]). Thirdly, it is not optimal to place the sampling point at the highest point.…”

“…Thirdly, it is not optimal to place the sampling point at the highest point. This is because carbon dioxide is heavier than other air components (approximately 44 g/mol in CO 2 compared to 32 g/mol in O 2 and 28 g/mol in N 2 ) and could accumulate there over time to a lesser extent than in the lower parts of the dead space of the mask [21]. In contrast, Butz provided a positioning of the sensor close to the mouth attached to the cheek [18], like Blad [20] and Sinkule [23], who placed it close to the breathing orifice (mouth opening), while Rhee and Roberge chose the nasolabial fold [25,27].…”

Large eddy simulation of cough jet dynamics, droplet transport, and inhalability over a ten minute exposure

“…Aerosol generation from coughs has inspired many studies to investigate the droplet-laden cough jet and puff dynamics through experimental and computational methods, 3–6 as well as review articles of the fluid dynamics of respiratory droplets 7–9 and mitigation strategies for reducing viral transmission. 10,11 …”

Infrared-based visualization of exhalation flows while wearing protective face masks

“…This result is in agreement with some current studies showing increased CO 2 levels inside an N95-type respirator. 29,30 …”