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Spatial Distribution of Ventilator Induced Lung Injury at the µm-Scale. An In-Vivo Synchrotron Phase-Contrast Microscopy Study in BALB/c Mice
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A7526 - Spatial Distribution of Ventilator Induced Lung Injury at the µm-Scale. An In-Vivo Synchrotron Phase-Contrast Microscopy Study in BALB/c Mice
Author Block: G. Lovric1, L. Broche2, C. M. Schleputz1, L. Fardin3, J. C. Schittny4, A. S. Larsson5, S. Bayat6; 1Swiss Light Source, Paul Scherrer Institute, Villigen, Switzerland, 2X ray Imaging, ESRF, Grenoble, France, 3Biomedical Beamline-ID17, European Synchrotron Radiation Facility, Grenoble, France, 4Univ of Bern, Bern, Switzerland, 5Surgical Sciences, Uppsala University, Uppsala, Sweden, 6Dept. of Clinical Physiol., Grenoble University Hospital Center, Grenoble, France.
Rationale It is well known that acute respiratory distress syndrome and ventilator induced lung injury (VILI) are very heterogeneous conditions within the lungs. However, it is unknown how injury is initiated and distributed at alveolar level. Previous in vivo microscopy studies have been limited to alveoli at the surface of the lungs. We report an in vivo synchrotron radiation phase-contrast microscopy technique of intact lungs (SR-PCµCT), i.e. allowing in vivo microscopy not only on the surface, but in the central region of the lung. We describe the structural changes at the alveolar level before, during, and the end of injurious ventilation in adult BALB/c mice studied in vivo.
Methods For in vivo SR-PCµCT lung imaging, we have developed a prospective heartbeat-triggered gating technique. The most crucial settings are ultra-short single-projection exposure times (1-3 ms) as well as the time point within the cardiac cycle at which the images are taken. In 5 anesthetized, tracheotomized and mechanically ventilated mice, VILI was induced with peak-inspiratory pressures of 30 cmH2O; PEEP=0; RR=68 BPM; FiO2 = 1.0. Propagation-based SR-PCµCT was performed at the X02DA TOMCAT beamline of the Swiss Light Source with a pixel size of 2.9 µm. Cardiac gating was used to avoid heart-induced motion artifacts. Imaging was performed at PEEP 5 and 10 cmH2O at baseline, after 1 and 2 hours of injurious ventilation and post mortem.
Results Using SR-PCµCT, the acini, including alveoli and bronchioles, could be visualized not only at the pleural surface but deep within the lung tissue. Alveolar aeration or lack thereof could be assessed. In this VILI model, some alveolar regions were almost unaffected by VILI while interlobular and alveolar septa were thickened in other regions. VILI appears to develop in a heterogeneous fashion and is not only associated with collapse and edema but also with hyper-expansion close to the collapsed areas.
Conclusions Our data demonstrate for the first time the feasibility of imaging airway and alveolar structures with a pixel size of 2.9 µm in in vivo BALB/c mouse lung. We demonstrate in 3D the gradual development of VILI at the alveolar scale in an injurious ventilation model. We hypothesize that the VILI starts at several small foci which grow by time due to hyper-expansion of the surrounding areas. This high resolution imaging technique sets the stage for a wide spectrum of in vivo studies of the microscopic lung parenchyma in mouse models of pulmonary diseases.
Author Block: G. Lovric1, L. Broche2, C. M. Schleputz1, L. Fardin3, J. C. Schittny4, A. S. Larsson5, S. Bayat6; 1Swiss Light Source, Paul Scherrer Institute, Villigen, Switzerland, 2X ray Imaging, ESRF, Grenoble, France, 3Biomedical Beamline-ID17, European Synchrotron Radiation Facility, Grenoble, France, 4Univ of Bern, Bern, Switzerland, 5Surgical Sciences, Uppsala University, Uppsala, Sweden, 6Dept. of Clinical Physiol., Grenoble University Hospital Center, Grenoble, France.
Rationale It is well known that acute respiratory distress syndrome and ventilator induced lung injury (VILI) are very heterogeneous conditions within the lungs. However, it is unknown how injury is initiated and distributed at alveolar level. Previous in vivo microscopy studies have been limited to alveoli at the surface of the lungs. We report an in vivo synchrotron radiation phase-contrast microscopy technique of intact lungs (SR-PCµCT), i.e. allowing in vivo microscopy not only on the surface, but in the central region of the lung. We describe the structural changes at the alveolar level before, during, and the end of injurious ventilation in adult BALB/c mice studied in vivo.
Methods For in vivo SR-PCµCT lung imaging, we have developed a prospective heartbeat-triggered gating technique. The most crucial settings are ultra-short single-projection exposure times (1-3 ms) as well as the time point within the cardiac cycle at which the images are taken. In 5 anesthetized, tracheotomized and mechanically ventilated mice, VILI was induced with peak-inspiratory pressures of 30 cmH2O; PEEP=0; RR=68 BPM; FiO2 = 1.0. Propagation-based SR-PCµCT was performed at the X02DA TOMCAT beamline of the Swiss Light Source with a pixel size of 2.9 µm. Cardiac gating was used to avoid heart-induced motion artifacts. Imaging was performed at PEEP 5 and 10 cmH2O at baseline, after 1 and 2 hours of injurious ventilation and post mortem.
Results Using SR-PCµCT, the acini, including alveoli and bronchioles, could be visualized not only at the pleural surface but deep within the lung tissue. Alveolar aeration or lack thereof could be assessed. In this VILI model, some alveolar regions were almost unaffected by VILI while interlobular and alveolar septa were thickened in other regions. VILI appears to develop in a heterogeneous fashion and is not only associated with collapse and edema but also with hyper-expansion close to the collapsed areas.
Conclusions Our data demonstrate for the first time the feasibility of imaging airway and alveolar structures with a pixel size of 2.9 µm in in vivo BALB/c mouse lung. We demonstrate in 3D the gradual development of VILI at the alveolar scale in an injurious ventilation model. We hypothesize that the VILI starts at several small foci which grow by time due to hyper-expansion of the surrounding areas. This high resolution imaging technique sets the stage for a wide spectrum of in vivo studies of the microscopic lung parenchyma in mouse models of pulmonary diseases.
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