Effect of breathing pattern on nasal airflow, air conditioning, and gas clearance in a patient specific upper airway...

Breathing pattern influences not only pulmonary ventilation but also upper airway transport processes such as nasal heat exchange, sinus ventilation, and carbon dioxide clearance. This study used transient computational fluid dynamics to investigate how respiratory rate and waveform shape affect these processes in a single patient specific upper airway model.

A computed tomography (CT) derived upper airway model from one healthy adult male, extending from the nasal vestibule to the nasopharynx and including the maxillary sinuses, was used as a fixed anatomical model. Five healthy respiratory profiles with respiratory rates of 45, 35, 25, 18, and 15 breaths⋅min^-1, together with two distinct chronic obstructive pulmonary disease (COPD) type breathing profiles at 18 breaths⋅min^-1, were applied to isolate the effect of breathing waveform from intersubject anatomical variability. Transient CFD simulations were performed over five complete breathing cycles to capture unsteady airflow and scalar transport.

Breathing frequency and waveform shape influenced airflow organisation, thermal conditioning, and gas exchange efficiency. Higher respiratory rates produced stronger but less uniform nasal velocities, greater mucosal cooling, and increased CO₂ rebreathing, reaching about 16%. Lower respiratory rates reduced rebreathing to below 6% by increasing tidal volume relative to the fixed upper airway dead space. Sinus ventilation and nitric oxide (NO) transport were strongly influenced by ostium size and breathing waveform. The left sinus, with the smaller ostium, remained predominantly diffusion limited, whereas the sinus with the larger ostium showed intermittent convective exchange during inhalation. Among the two COPD type breathing profiles, the waveform with the shorter inspiratory phase showed the weakest thermal recovery and lowest inhaled air temperature, whereas the less abrupt waveform remained closer to the corresponding healthy case at the same respiratory rate.

The present simulations show that breathing pattern influences intranasal airflow, air conditioning, rebreathed gas clearance, and sinus ventilation. Lower respiratory rates improved gas clearance by reducing the relative effect of anatomical dead space, while waveform differences also affected heat exchange and sinus transport. The findings should be interpreted as a mechanistic, case specific assessment of waveform effects rather than a population level comparison between healthy and COPD subjects.