Local Strain Distribution in Real Three-Dimensional Alveolar Geometries

Abstract

Mechanical ventilation is not only a life saving treatment but can also cause negative side effects. One of the main complications is inflammation caused by overstretching of the alveolar tissue. Previously, studies investigated either global strains or looked into which states lead to inflammatory reactions in cell cultures. However, the connection between the global deformation, of a tissue strip or the whole organ, and the strains reaching the single cells lining the alveolar walls is unknown and respective studies are still missing. The main reason for this is most likely the complex, sponge-like alveolar geometry, whose three-dimensional details have been unknown until recently. Utilizing synchrotron-based X-ray tomographic microscopy, we were able to generate real and detailed three-dimensional alveolar geometries on which we have performed finite-element simulations. This allowed us to determine, for the first time, a three-dimensional strain state within the alveolar wall. Briefly, precision-cut lung slices, prepared from isolated rat lungs, were scanned and segmented to provide a three-dimensional geometry. This was then discretized using newly developed tetrahedral elements. The main conclusions of this study are that the local strain in the alveolar wall can reach a multiple of the value of the global strain, for our simulations up to four times as high and that thin structures obviously cause hotspots that are especially at risk of overstretching.

Submicron particle deposition in pulmonary alveoli during cyclic breathing

“…The maximum value for local stretch is about 1.2 occurring at t = 1:4, which is in agreement with the X-ray microscopy performed by Raush et al [22]. We have presented more results about alveolus mechanics elsewhere [23].…”

Fluid-structure interaction analysis of air flow in pulmonary alveoli during normal breathing in healthy humans

“…The maximum global stress and strain in the time of t = 1:4 s are 1 kPa and 0.05, respectively, while in hotspots the maximum stress and strains reach to 2 kPa and 0.2. Rausch et al [33], utilizing synchrotron-based X-ray tomographic microscopy, also found a maximum local strain of 0.2.…”

Regional distribution of lung compliance by image analysis of computed tomograms

“…However, if different areas have different compliances, the mechanical interaction (and thus the impact on organ health) between them depend on the distance at which they are located. If they are bordering, a difference in their time constants may generate very high transmural pressure gradients; if they are far apart, mechanical differences may have a negligible impact on organ biology (Mead et al, 1970;Plataki and Hubmayr, 2010;Rausch et al, 2011). Thus, we used quadtree decomposition to assess how much these compliance values were intermingled.…”