Examining lung mechanical strains as influenced by breathing volumes and rates using experimental digital image correlation

Abstract

Background Mechanical ventilation is often employed to facilitate breathing in patients suffering from respiratory illnesses and disabilities. Despite the benefits, there are risks associated with ventilator-induced lung injuries and death, driving investigations for alternative ventilation techniques to improve mechanical ventilation, such as multi-oscillatory and high-frequency ventilation; however, few studies have evaluated fundamental lung mechanical local deformations under variable loading. Methods Porcine whole lung samples were analyzed using a novel application of digital image correlation interfaced with an electromechanical ventilation system to associate the local behavior to the global volume and pressure loading in response to various inflation volumes and breathing rates. Strains, anisotropy, tissue compliance, and the evolutionary response of the inflating lung were analyzed. Results Experiments demonstrated a direct and near one-to-one linear relationship between applied lung volumes and resulting local mean strain, and a nonlinear relationship between lung pressures and strains. As the applied air delivery volume was doubled, the tissue surface mean strains approximately increased from 20 to 40%, and average maximum strains measured 70–110%. The tissue strain anisotropic ratio ranged from 0.81 to 0.86 and decreased with greater inflation volumes. Local tissue compliance during the inflation cycle, associating evolutionary strains in response to inflation pressures, was also quantified. Conclusion Ventilation frequencies were not found to influence the local stretch response. Strain measures significantly increased and the anisotropic ratio decreased between the smallest and greatest tidal volumes. Tissue compliance did not exhibit a unifying trend. The insights provided by the real-time continuous measures, and the kinetics to kinematics pulmonary linkage established by this study offers valuable characterizations for computational models and establishes a framework for future studies to compare healthy and diseased lung mechanics to further consider alternatives for effective ventilation strategies.

Mouse lung mechanical properties under varying inflation volumes and cycling frequencies

“…The increase in static compliance is unexpected because it indicates a softer lung that is easier to inflate at higher volumes. Lung tissue is known to experience strain-stiffening which would cause a decrease in static compliance, a stiffer lung, at higher inflation volumes 40 , 41 ; this effect has been demonstrated on the surface of the murine lung during inflation at 0.7 and 0.9 ml using digital image correlation, which allows analysis of simultaneous global and local behavior 42 , 43 . However, increasing the internal space available within the lung, as caused by the opening of a secondary (daughter) set of alveoli, would create more regions for air migration, alleviating the excess strain on alveoli and thus increasing the static compliance 36 , 44 .…”

Associating local strains to global pressure–volume mouse lung mechanics using digital image correlation

“…Strain heterogeneity increases with increasing applied volumes, as seen by the significantly expanding strain range and significantly increasing standard deviation from 0.3 to 0.7 ml for both breathing rates (Figures 2 and 3) and is consistent with previous murine studies (Arora et al, 2021; Mariano et al, 2020). Dominant regions of preferential strain development have been observed in porcine specimens, where the upper region of the lung exhibits the highest strains (Maghsoudi‐Ganjeh et al, 2021; Mariano et al, 2022). However, given lung lobe morphology differences, significant size discrepancies between species, and mechanical distinctions (i.e., collateral ventilation phenomena), findings from porcine lungs cannot necessarily be extended to mouse lungs.…”

Lung Mechanics: A Review of Solid Mechanical Elasticity in Lung Parenchyma

“…This has resulted in more refined investigations attempting to improve on the techniques currently implemented in mechanical ventilation. These include multi-oscillatory and high-frequency ventilation [ 121 ]. Although, there exist few studies which have analysed lung mechanical deformations under variable loading.…”

“…[ 121 ] addresses this gap through the use digital image correlation (DIC) to characterise ventilation strains more effectively. Digital volume correlation (DVC), optical computed tomography (OCT), and elastography have commonly been used to provide strain measurement values [ 69 , 104 ], however, these techniques are time sensitive which significantly affects the reported lung behaviour [ 121 ]. On the other hand, digital image correlation analysis is a novel method for analysing topological deformations during porcine lung inflation [ 121 ].…”

“…Digital volume correlation (DVC), optical computed tomography (OCT), and elastography have commonly been used to provide strain measurement values [ 69 , 104 ], however, these techniques are time sensitive which significantly affects the reported lung behaviour [ 121 ]. On the other hand, digital image correlation analysis is a novel method for analysing topological deformations during porcine lung inflation [ 121 ]. Mariano et al.…”