Local tissue strain imaged by in vivo 4D phase-contrast µCT in bleomycin and ventilator-induced lung injury in rats

<bold>Introduction:</bold> Mechanical ventilation can induce lung injury due to exaggerated strain on lung tissue (ventilator-induced lung injury: VILI). We investigated the effect of injurious ventilation on local strain, using 4D-phase-contrast µCT, in anesthetized and ventilated rats. <bold>Methods:</bold> 6 control and 7 bleomycin-injured (Bleo) rats at 7 days, were anesthetized and ventilated in pressure control. CT was performed with a pixel size of 6 µm and 10 ms resolution. Respiratory mechanics were measured using forced oscillations. After baseline imaging, peak airway pressure was increased to 40 cmH2O for 20 min and imaging was repeated. Quantitative maps of local lung strain were computed using image-registration based image processing. <fig><object-id>erj;64/suppl_68/PA3388/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig> <bold>Results:</bold> Fig. 1A shows quantitative strain maps in a representative control and bleomycin-injured rat pre- and post-VILI. Respiratory elastance was significantly increased in Bleo vs. Control (Fig. 1B) and increased post-VILI. Average maximum local strain (Fig. 1C) was significantly lower in Bleo vs. Control, and did not significantly change post-VILI. <bold>Conclusions:</bold> Stiffer lungs due to bleomycin-induced lung injury translated into reduced local lung tissue strain both at baseline and after VILI, under pressure-controlled ventilation. This model will allow investigation of the effect of local tissue strain and the alterations that occur in the extracellular matrix, quantitatively.