Evidence for age-dependent air-space enlargement contributing to loss of lung tissue elastic recoil pressure and increased shear modulus in older age

Abstract

As a normal part of mature aging, lung tissue undergoes microstructural changes such as alveolar air-space enlargement and redistribution of collagen and elastin away from the alveolar duct. The older lung also experiences an associated decrease in elastic recoil pressure and an increase in specific tissue elastic moduli, but how this relates mechanistically to microstructural remodeling is not well-understood. In this study, we use a structure-based mechanics analysis to elucidate the contributions of age-related air-space enlargement and redistribution of elastin and collagen to loss of lung elastic recoil pressure and increase in tissue elastic moduli. Our results show that age-related geometric changes can result in reduction of elastic recoil pressure and increase in shear and bulk moduli, which is consistent with published experimental data. All elastic moduli were sensitive to the distribution of stiffness (representing elastic fiber density) in the alveolar wall, with homogenous stiffness near the duct and through the septae resulting in a more compliant tissue. The preferential distribution of elastic proteins around the alveolar duct in the healthy young adult lung therefore provides for a more elastic tissue. We use a structure-based mechanics analysis to correlate air-space enlargement and redistribution of elastin and collagen to age-related changes in the mechanical behavior of lung parenchyma. Our study highlights that both the cause (redistribution of elastin and collagen) and the structural effect (alveolar air-space enlargement) contribute to decline in lung tissue elastic recoil with age; these results are consistent with published data and provide a new avenue for understanding the mechanics of the older lung.

The micromechanics of lung alveoli: structure and function of surfactant and tissue components

“…In this context, aging has been shown to result in airspace enlargement and reduction in elastic recoil of the lung. These observations have recently been suggested to be explainable by a pure age-related redistribution of elastic and collagen fibers within the inter-alveolar septa “away from the alveolar duct” emphasizing the relevance of the spatial distribution and orientation of the fiber networks (Subramaniam et al 2017 ).…”

Aging Effects on Alveolar Sacs Under Mechanical Ventilation

“…Moreover, an increase in alveolar wall thickness has been observed in older subjects in previous experimental studies (5,6,11,12). In addition to the structural changes, aging imposes material properties changes on alveolar sacs (4)(5)(6) and this leads to an increase in tissue bulk and shear modulus (4,5,9).…”

“…Accordingly, applied pressure in a volume-controlled mode in this study was recorded as 10 cmH 2 O for the 50-year-old and 2 cmH 2 O for the 80-year-old cases during inhalation while this value was decreased while exhaling air. Subramaniam et al (9) presented volume increase from reference volume. Results for volume changes from reference volume for the same amount of applied pressure on the alveolar sacs wall were compared with results from Subramaniam et al study (9).…”

“…Subramaniam et al (9) presented volume increase from reference volume. Results for volume changes from reference volume for the same amount of applied pressure on the alveolar sacs wall were compared with results from Subramaniam et al study (9). Lower pressure values resulted in lower volume changes for the same amount of applied pressure on the alveolar sacs wall.…”

“…Generally, aging induces morphological and tissue property changes in human alveolar sacs. These changes influence alveolar sacs mechanics and gas exchange (1,(7)(8)(9)(10). Quirk et al (6) used MRI with hyperpolarized 3 He and detected age-dependent morphological changes in the acinar region.…”