Investigation of the Effects of Emphysema and Influenza on Alveolar Sacs Closure through CFD Simulation

Emphysema and influenza directly affect alveolar sacs and cause problems in lung performance during the breathing cycle. In this study, the effects of Emphysema and Influenza on alveolar sac’s air flow characteristics are investigated through Computational Fluid Dynamics (CFD) simulation. Both normal and Emphysemic alveolar sac models with varying collapsed volumes resulting from influenza virus replication were developed. Maximum, area average pressure, and wall shear stress (WSS) in collapsed and open alveolar sacs models were compared. It was found that a collapse at half of the volume at the bottom of the alveolar sacs’ models would cause a decrease in average and maximum pressure values and yield higher WSS values for fluid flow during the breathing cycle. On the other hand, a quarter volume collapse at the bottom and side of the model resulted in higher values for average and maximum pressure and WSS. Additionally, results also showed that a combination of alveolar sacs closure and Emphysema would generally lead to an increase in fluid pressure and average WSS during breathing. Maximum WSS was observed during exhalation and maximum WSS decrease occurred during inhalation. Findings are in good agreement with previous studies and suggest that emphysema and influenza virus affect fluid flow and may contribute to alveolar sac closure. However, more realistic simulations should include the fluid-solid interaction studies.

Effect of off-axis cell orientation on mechanical properties in smooth muscle tissue

The cell alignment in a smooth muscle tissue plays a significant role in determining its mechanical proper-ties. The off-axis cell orientation 'θ” not only effects the shortening strain but also modifies the shear stress relationship significantly. Both experiments and finite element analysis were carried out on a tracheal smooth muscle strip to study how the cell alignment in smooth muscle affects the shear stiffness and shear stresses as well as deformation. A simple model for shear stiffness is derived using the data from experiments. Shear stiffness results obtained from the model indicate that the muscle shear stiff-ness values increase non-linearly with strain and with higher off-axis alignment of cells. Results of deforma-tion and shear stresses obtained from finite element analsysis indicate that the maximum shear stress values of tracheal smooth muscle tissue at 45% of strain are 2.5 times the corresponding values at 20% of strain for all three off-axis cell orientation values θ = 15?, 30? and 45?.

Analysis for stress environment in the alveolar sac model

Better understanding of alveolar mechanics is very important in order to avoid lung injuries for patients undergoing mechanical ventilation for treatment of respiratory problems. The objective of this study was to investigate the alveolar mechanics for two different alveolar sac models, one based on actual geometry and the other an idealized spherical geometry using coupled fluid-solid computational analysis. Both the models were analyzed through coupled fluid-solid analysis to estimate the parameters such as pressures/ velocities and displacements/stresses under mechanical ventilation conditions. The results obtained from the fluid analysis indicate that both the alveolar geometries give similar results for pressures and velocities. However, the results obtained from coupled fluid-solid analysis indicate that the actual alveolar geometry results in smaller displacements in comparison to a spherical alveolar model. This trend is also true for stress/strain between the two models. The results presented indicate that alveolar geometry greatly affects the pressure/velocities as well as displacements and stresses/strains.