New insights into the breathing physiology from transient respiratory nasal simulation

Abstract

We investigated the flow characteristics and heat transfer during nasal breathing in the complete human upper airway through the respiratory cycle using transient numerical simulations. We postulate the complete airway from the nasal cavity to the trachea most accurately represents dynamic airflow patterns during inhalation and exhalation as they are likely to be affected by downstream anatomical structures. We constructed a 3-Dimensional model from a healthy adult computed tomography (CT) scan. Computational Fluid Dynamics simulations were performed with Ansys Fluent software using the Stress-Blended Eddy Simulation (SBES) turbulence model, looking at airflow patterns, velocity, mucosal temperature and humidity (H2O fraction). We simulated one-and-a-half breathing cycles (5.65 seconds) and discarded the first inhalation cycle to avoid start-up effects. The results demonstrated that airway geometry structures, including the turbinates, the soft palate and the glottic region, affect the flow patterns differently during inspiration and expiration. It also demonstrated phenomena not seen in steady flow simulations or those without the lower respiratory tract geometry, including the nasopharyngeal temperature imprint during inhalation, the nasopharyngeal jet during exhalation and the flow structures of the larynx and laryngeal jet. The inclusion of the exhalation phase demonstrates airflow pre-conditioning before inhalation, which we postulate contributes to achieving alveolar conditions. Alveolar temperature and humidity conditions are not achieved by the nasal cavity alone, and we demonstrate the contribution of the nasopharynx and larynx to air conditioning. Including the complete airway with realistic anatomy and using transient airflow modelling provided new insights into the physiology of the respiratory cycle.

Computational Rhinology: Unraveling Discrepancies between In Silico and In Vivo Nasal Airflow Assessments for Enhanced Clinical Decision Support

“…Due to the narrow passage connecting the paranasal sinuses with the nasal cavity, it is expected that negligible gas exchange takes place between the two [ 171 ]. This was supported by simulation results presented by Bradshaw et al [ 159 ]. Kaneda et al [ 126 ] reported that the inclusion of the paranasal sinuses did not improve the disagreement between computed and measured nasal resistances.…”

“…Furthermore, they observed that asymmetry in the respiratory cycle had little effect on the flow pattern in the nasal cavity compared to a sinusoidal inhalation/exhalation profile, which follows naturally from quasi-steady behavior. Bradshaw et al [ 159 ] highlighted several phenomena observed in their transient simulations that cannot be seen in steady flow. In particular, their results indicate that transient simulations of the entire breathing cycle are essential in order to correctly capture air conditioning via heating/cooling and humidification.…”

“…They suggested that LES or DNS is necessary to reliably simulate the full breathing cycle at intermediate intensity. Bradshaw et al [ 159 ] performed hybrid RANS-LES simulations of the entire respiratory cycle and reported bilateral nasal airflow to be dominantly laminar. While LES is widely acknowledged as one of the most accurate turbulence modelling approaches, second only to DNS, it is worth noting that LES also encounters challenges in predicting transitional flow and the initiation of turbulence, as highlighted by Sayadi and Moin [ 169 ].…”

Effect of ambient temperature and respiration rate on nasal dominance: preliminary findings from a nostril-specific wearable

“…The ND is a physiological variation of congestion and decongestion of the nasal mucosa of both the right and left nostrils over 30 min to several hours [3]. Nearly 80% of the healthy population shows a regular cycle [42].…”

“…A fundamental component of biological function is the rhythmic events ranging from subcellular elements to the entire organism. One such rhythm present in the nasal breathing of mammals is the nasal cycle [1][2][3][4]. The nasal cycle is the spontaneous congestion and decongestion of the nasal mucosa, where congestion of one side is accompanied by reciprocal decongestion of the contralateral side.…”