Relaxation and creep response of the alveolar lung to diagnosis and treatments for respiratory and lung disorders.

Background: The lung Extracellular Matrix (ECM) contains a considerable part of the parenchymal cells. It contains three essential components: elastin and collagen within a proteoglycan (PG) viscoelastic network. Elastin provides the lung's elasticity property, a necessity for normal breathing, while collagen prepares structural support and strength, and PGs give stability and cushioning within tissue loading. Bacterial and viral respiratory diseases are dependent on changes in the ECM ingredients, which result in an alteration of the lung tissue strength. Purpose: In the present study, this variation was investigated by changing the volume ratio of the ECM ingredients in the viscoelastic model. Results: As a result, the relaxation curves continuously declined by reducing the volume ratios of elastin, collagen, and PGs; subsequently, the lung stiffness decreased. Also, the Standard Linear Solid (SLS) model-based results demonstrated excellent accordance with empirical data with only minor deviations. The resting relaxation modulus and the creep modulus for the ECM tissue were 51 kPa and approximately 0.02 kPa, respectively, and the maximum total modulus of elasticity reached 121 kPa. Conclusions: Moreover, this model demonstrates individual alveolar mechanical behaviours and adds another pathway to the generalized Kelvin-Voigt and Maxwell models in predicting the progress of lung diseases. [ABSTRACT FROM AUTHOR]