The influence of tethering and gravity on the stability of compliant liquid-lined airways

Abstract

This study revolves around two simple questions: 1) how does pulmonary airway recruitment/de-recruitment (RecDer) depend on the tethering support provided by surrounding airways and alveoli, and 2) does airway angle of inclination (θ) influence airway stability? These two questions are critical to understanding the existence and prevention of atelectrauma, which may contribute to ventilator-induced lung injury (VILI). To address these questions, we develop PDMS 2mm ID compliant tubes that mimic pulmonary airways. Airway obstruction is modeled using silicone oil, and recruitment occurs through insufflation with a constant flow of air at Q=0.25ml/s. Parenchymal tethering is modeled through the use of a pressure chamber through which we independently establish the external pressure (P). Repetitive RecDer oscillation is observed as a function of P and θ. We find that airway collapse significantly increases the rate of instability, and this rate correlates strongly with the dimensionless film thickness (ε=h/R), where h is the film thickness and R is the transumural pressure dependent vessel radius. Furthermore, the angle of orientation influences RecDer oscillation, with stability decreased when airflow is directed in the upward direction. These results may provide insight into protective mechanical ventilation processes that can reduce the existence or severity of VILI.

Microscale distribution and dynamic surface tension of pulmonary surfactant normalize the recruitment of asymmetric bifurcating airways

“…This would introduce segments of trapped gas and multiple interfaces that could alter the system behavior. The structural compliance was also not investigated; clearly this would modify the geometry and interfacial instabilities based upon the local pressure (41). In reality, the terminal bronchioles and acini impose elastic resistance (P End ) that may act to balance the resistances and lead to symmetric reopening depending on the magnitudes of P Hyd and P Cap .…”

Potential effect of pulmonary fluid viscosity on positive end-expiratory pressure and regional distribution of lung ventilation in acute respiratory distress syndrome

“…The optimal level of PEEP, however, remains debated. From a mechanical point of view, the levels of the pressure (P) needed to open a small airway or an alveolus are determined by the tissue tethering force ( ), hydrostatic pressure ( ℎ ), the surface tension at the air-liquid interface ( ) and viscous pressure from pulmonary fluids ( ) (Chen et al 2015;Whang et al 2017), as stated in the following equation:…”