Assessment of mechanical ventilation parameters on respiratory mechanics

Abstract

Better understanding of airway mechanics is very important in order to avoid lung injuries for patients undergoing mechanical ventilation for treatment of respiratory problems in intensive-care medicine, as well as pulmonary medicine. Mechanical ventilation depends on several parameters, all of which affect the patient outcome. As there are no systematic numerical investigations of the role of mechanical ventilation parameters on airway mechanics, the objective of this study was to investigate the role of mechanical ventilation parameters on airway mechanics using coupled fluid-solid computational analysis. For the airway geometry of 3 to 5 generations considered, the simulation results showed that airflow velocity increased with increasing airflow rate. Airway pressure increased with increasing airflow rate, tidal volume and positive end-expiratory pressure (PEEP). Airway displacement and airway strains increased with increasing airflow rate, tidal volume and PEEP form mechanical ventilation. Among various waveforms considered, sine waveform provided the highest airflow velocity and airway pressure while descending waveform provided the lowest airway pressure, airway displacement and airway strains. These results combined with optimization suggest that it is possible to obtain a set of mechanical ventilation strategies to avoid lung injuries in patients.

Analysis for stress environment in the alveolar sac model

“…the local computational control-volume size, ρ g is the fluid density, p is the fluid pressure, μ is the fluid viscosity, and u is the fluid velocity [1,2]. …”

“…In the equations above σ is the stress in each direction, F is the body force, ρ is the density, u is the displacement, C is the elasticity tensor, and ε is the strain in each direction [1,2]. …”

“…ANSYS Mechanical is a general finite element (FE) software program for structural modeling, and ANSYS CFX is a general purpose computational fluid dynamics (CFD) software program for modeling fluid flows. The individual models were coupled using a fluid-structure interaction (FSI) algorithm [2]. Analysis assumed the solid portion was compliant, i.e.…”

“…For the alveolar sac model, the wall was assumed to be made of a homogeneous and linearly elastic material [1,2]. The wall has a density of 196 kg/m 3 , Young’s Modulus of 5 kPa, and a Poisson’s ratio of 0.4 [7].…”

“…These conditions include volutrauma/barotrauma (extreme stress/strain), atelectrauma (repeated opening and closing of collapsed alveoli) and biotrauma. If the aforementioned conditions are increased multi-system organ failure (MSOF) can occur [1,2]. …”