Effects of respiratory rate on the fluid mechanics of a reconstructed upper airway

Abstract

This study aims to utilise particle image velocimetry (PIV) techniques to investigate the time-dependant effects of respiratory rate in the extrathoracic airway, to show how they affect the flow field developed. There has been limited validation of computational fluid dynamics (CFD) models using experimental setups. Furthermore, the large majority of existing CFD models focus on rigid airways, not accounting for active deformation through the breathing cycle. Experiments were carried out to expand upon Zhao et al.'s previous study, in which a single respiratory rate was investigated. This studied utilised a transient, sinusoidal flow profile with two respiratory rates of 10 breaths per minute (BPM) and 25 BPM, both achieving a maximum flow rate correlating to 5 L/min in air to simulate tidal breathing. Results from this study showed that respiratory rate had the greatest influence near the onset of the inspiratory and expiratory manoeuvres, with the higher respiratory rate homogenising later in the cycle. It was shown that airway deformation at the level of the soft palate homogenised flow downstream of the deformation which resulted in a lower peak magnitude velocity for approximately 40% of the cycle at the level of the epiglottis, when compared to the rigid airway model.

Keywords: Active deformation; Airways; Breathing frequency; Deformable airway; Epiglottis; Expiratory; Extra-thoracic; Fllow Field; Flow homogeny; Inspiratory; MRI; MRI reconstructed upper airway model; Particle image velocimetry; Patency; Pulsatile; Respiratory rate; Reynolds; Rigid model; Tidal breathing; Womersley.