Streaming Caused by Oscillatory Flow in Peripheral Airways of Human Lung

Abstract

Oscillatory flow facilitates gas exchange in human respiration system. In the present study, both numerical calculation and PIV (Particle Image Velocimetry) measurement indicate that, under the application of HFOV (High Frequency Oscillatory Ventilation), apparent steady streaming is caused and augmented in distal airways by the continuous oscillation, i.e., the core air moves downwards and the peripheral air evacuates upwards within bronchioles. The net flow of steady streaming serves to overcome the lack of tidal volume in HFOV and delivers fresh air into deeper lung region. Also, numerical calculations reveal that the intensity of steady streaming is mainly influenced by the geometry of airways with provided oscillatory frequency and tidal volume, and it rises with Re and Wo up to a Re of about 124 and Wo of about 5. Steady streaming is considered as an important factor for the ventilation efficiency of HFOV.

Revisiting high-frequency oscillatory ventilation in vitro and in silico in neonatal conductive airways

“…This lack of flow reversibility causes fluid to migrate to different axial locations after each cycle (Tanaka et al, 2001). Notably, Han et al (2016) analysed such streaming behaviour in a planar, symmetric double bifurcation model under CMV and HFOV conditions. They presented numerical results of the net displacement of Lagrangian (fluid) particles, where streaming strongly increased at higher frequencies.…”

Mean streaming in reciprocating flow in a double bifurcation

“…A recent in-depth experimental study of the flow in a double-bifurcation (Jalal et al 2018) indicated that the mean streaming flow is small in magnitude compared to the peak oscillating flow and provided some evidence that mean streaming may decrease with increasing frequency. However, another numerical and experimental study (Han et al 2016) showed that mean streaming can transport gas over distances far further than the 'stroke' length (the distance that fluid would be transported if it simply moved as a block of fixed volume up and down the flow domain). Further, Han et al (2016) showed that multi-generation bifurcating tubes generate stronger mean streaming in their upper generations compared to single bifurcations.…”

“…However, another numerical and experimental study (Han et al 2016) showed that mean streaming can transport gas over distances far further than the 'stroke' length (the distance that fluid would be transported if it simply moved as a block of fixed volume up and down the flow domain). Further, Han et al (2016) showed that multi-generation bifurcating tubes generate stronger mean streaming in their upper generations compared to single bifurcations.…”

Effects of Varying Inhalation Duration and Respiratory Rate on Human Airway Flow

“…where ω = 2π/BT is the angular frequency based on breathing time (BT, where BT = 60/RR seconds), D is the tracheal diameter, and ν is the kinematic viscosity of air. RR can be altered from the resting range of 10-15 bpm during exercise (such as walking RR = 20-60 bpm [4] and yoga RR = 3-7 bpm [5]), and also in mechanical ventilation strategies, such as highfrequency oscillatory ventilation (HFOV) [6][7][8]. Further, inhalation time (IT) is about 45% of BT under normal breathing conditions [6].…”