Abstract
BackgroundProtective mechanical ventilation (MV) aims at limiting global lung deformation and has been associated with better clinical outcomes in acute respiratory distress syndrome (ARDS) patients. In ARDS lungs without MV support, the mechanisms and evolution of lung tissue deformation remain understudied. In this work, we quantify the progression and heterogeneity of regional strain in injured lungs under spontaneous breathing and under MV.MethodsLung injury was induced by lung lavage in murine subjects, followed by 3 h of spontaneous breathing (SB-group) or 3 h of low Vt mechanical ventilation (MV-group). Micro-CT images were acquired in all subjects at the beginning and at the end of the ventilation stage following induction of lung injury. Regional strain, strain progression and strain heterogeneity were computed from image-based biomechanical analysis. Three-dimensional regional strain maps were constructed, from which a region-of-interest (ROI) analysis was performed for the regional strain, the strain progression, and the strain heterogeneity.ResultsAfter 3 h of ventilation, regional strain levels were significantly higher in 43.7% of the ROIs in the SB-group. Significant increase in regional strain was found in 1.2% of the ROIs in the MV-group. Progression of regional strain was found in 100% of the ROIs in the SB-group, whereas the MV-group displayed strain progression in 1.2% of the ROIs. Progression in regional strain heterogeneity was found in 23.4% of the ROIs in the SB-group, while the MV-group resulted in 4.7% of the ROIs showing significant changes. Deformation progression is concurrent with an increase of non-aerated compartment in SB-group (from 13.3% ± 1.6% to 37.5% ± 3.1%), being higher in ventral regions of the lung.ConclusionsSpontaneous breathing in lung injury promotes regional strain and strain heterogeneity progression. In contrast, low Vt MV prevents regional strain and heterogeneity progression in injured lungs.
Highlights
Protective mechanical ventilation (MV) aims at limiting global lung deformation and has been associ‐ ated with better clinical outcomes in acute respiratory distress syndrome (ARDS) patients
Statistical and image analysis was carried out using five subjects in the SB-group and five subjects in the MV-group due to the following considerations: (i) mortality in the SB-group was high, with three out of nine subjects dying before completing the observation period and image acquisition; and (ii) the Com‐ puted tomography (CT) images acquired in one animal of each group displayed a notorious alteration of the thoracic–abdominal region, preventing a reliable analysis
endexpiratory lung volume (EELV), Minute ventilation (Vmin), Tidal volume (Vt), and global strain were obtained from image analysis of μ-CT images No significant changes were detected between T1 to T3 in any of the groups increase in regional volumetric strain in 38 out of 87 regions of interest (ROIs) (43.7%), which were predominantly located in the basal-dorsal quadrant (Fig. 2b, d)
Summary
Protective mechanical ventilation (MV) aims at limiting global lung deformation and has been associ‐ ated with better clinical outcomes in acute respiratory distress syndrome (ARDS) patients. A spatial correlation between areas of increased regional strain and areas of tissue inflammation has been found in a high global strain model, demonstrating the potential role of regional biomechanical behaviors in the progression of lung injury [2]. Considering these findings, a better understanding of the spatiotemporal progression of regional strain and heterogeneity may be the key to avoid progression of damage to the lungs during respiratory failure [3]
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