Mapping regional strain in anesthetised healthy subjects during spontaneous ventilation

Abstract

IntroductionBreathing produces a phenomenon of cyclic deformation throughout life. Biomechanically, deformation of the lung is measured as strain. Regional strain recently started to be recognised as a tool in the study of lung pathophysiology, but regional lung strain has not been studied in healthy subjects breathing spontaneously without voluntary or pharmacological control of ventilation. Our aim is to generate three-dimensional (3D) regional strain and heterogeneity maps of healthy rat lungs and describe their changes over time.MethodsMicro-CT and image-based biomechanical analysis by finite element approach were carried out in six anaesthetised rats under spontaneous breathing in two different states, at the beginning of the experiment and after 3 hours of observation. 3D regional strain maps were constructed and divided into 10 isovolumetric region-of-interest (ROI) in three directions (apex to base, dorsal to ventral and costal to mediastinal), allowing to regionally analyse the volumetric strain, the strain progression and the strain heterogeneity. To describe in depth these parameters, and systematise their report, we defined regional strain heterogeneity index [1+strain SD ROI(x)]/[1+strain mean ROI(x)] and regional strain progression index [ROI(x)−mean of final strain/ROI(x)−mean of initial strain].ResultsWe were able to generate 3D regional strain maps of the lung in subjects without respiratory support, showing significant differences among the three analysed axes. We observed a significantly lower regional volumetric strain in the apex sector compared with the base, with no significant anatomical systematic differences in the other directions. This heterogeneity could not be identified with physiological or standard CT methods. There was no progression of the analysed regional volumetric strain when the two time-points were compared.DiscussionIt is possible to map the regional volumetric strain in the lung for healthy subjects during spontaneous breathing. Regional strain heterogeneity and changes over time can be measured using a CT image-based numerical analysis applying a finite element approach. These results support that healthy lung might have significant regional strain and its spatial distribution is highly heterogeneous. This protocol for CT image acquisition and analysis could be a useful tool for helping to understand the mechanobiology of the lung in many diseases.

Progression of regional lung strain and heterogeneity in lung injury: assessing the evolution under spontaneous breathing and mechanical ventilation

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Polymeric Tissue Adhesives

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A physiological approach to understand the role of respiratory effort in the progression of lung injury in SARS-CoV-2 infection

“…Recently, we developed a 4D tomographic study that employs image-based biomechanical analysis [49] to unveil the volumetric distribution of regional deformation of the whole lung in subjects without MV. In healthy sedated rats under (unassisted) spontaneously breathing, we observed volumetric regional strain and strain heterogeneity, quantifying the magnitude of these deformation indices and its progression in time [50]. Given the fact that regional strain and heterogeneity are present during a normal respiratory cycle without harming the lung leads to the question: why P-SILI does not develop in normal lungs deformed by physiologic Vt?…”