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- Broche, Ludovic, et al.
(författare)
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Dynamic Mechanical Interactions Between Neighboring Airspaces Determine Cyclic Opening and Closure in Injured Lung
- 2017
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Ingår i: Critical Care Medicine. - 0090-3493 .- 1530-0293. ; 45:4, s. 687-694
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Positive pressure ventilation exposes the lung to mechanical stresses that can exacerbate injury. The exact mechanism of this pathologic process remains elusive. The goal of this study was to describe recruitment/derecruitment at acinar length scales over short-time frames and test the hypothesis that mechanical interdependence between neighboring lung units determines the spatial and temporal distributions of recruitment/derecruitment, using a computational model. Design: Experimental animal study. Setting: International synchrotron radiation laboratory. Subjects: Four anesthetized rabbits, ventilated in pressure controlled mode. Interventions: The lung was consecutively imaged at - 1.5-minute intervals using phase-contrast synchrotron imaging, at positive end expiratory pressures of 12, 9, 6, 3, and 0 cm H2O before and after lavage and mechanical ventilation induced injury. The extent and spatial distribution of recruitment/derecruitment was analyzed by subtracting subsequent images. In a realistic lung structure, we implemented a mechanistic model in which each unit has individual pressures and speeds of opening and closing. Derecruited and recruited lung fractions (F-derecruaed, F-recruited) were computed based on the comparison of the aerated volumes at successive time points. Measurements and Main Results: Alternative recruitment/derecruitment occurred in neighboring alveoli over short-time scales in all tested positive end-expiratory pressure levels and despite stable pressure controlled mode. The computational model reproduced this behavior only when parenchymal interdependence between neighboring acini was accounted for. Simulations closely mimicked the experimental magnitude of F-derecruited and F-recruited when mechanical interdependence was included, while its exclusion gave F-recruited values of zero at positive end -expiratory pressure greater than or equal to 3 cm H2O. Conclusions: These findings give further insight into the microscopic behavior of the injured lung and provide a means of testing protective-ventilation strategies to prevent recruitment/derecruitment and subsequent lung damage.
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- Broche, Ludovic, et al.
(författare)
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Individual Airway Closure Characterized In Vivo by Phase-Contrast CT Imaging in Injured Rabbit Lung
- 2019
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Ingår i: Critical Care Medicine. - : LIPPINCOTT WILLIAMS & WILKINS. - 0090-3493 .- 1530-0293. ; 47:9, s. E774-E781
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Airway closure is involved in adverse effects of mechanical ventilation under both general anesthesia and in acute respiratory distress syndrome patients. However, direct evidence and characterization of individual airway closure is lacking. Here, we studied the same individual peripheral airways in intact lungs of anesthetized and mechanically ventilated rabbits, at baseline and following lung injury, using high-resolution synchrotron phase-contrast CT.Design: Laboratory animal investigation.Setting: European synchrotron radiation facility.Subjects: Six New-Zealand White rabbits.Interventions: The animals were anesthetized, paralyzed, and mechanically ventilated in pressure-controlled mode (tidal volume, 6 mL/kg; respiratory rate, 40; Fio(2), 0.6; inspiratory:expiratory, 1:2; and positive end-expiratory pressure, 3 cm H2O) at baseline. Imaging was performed with a 47.5 x 47.5 x 47.5 mu m voxel size, at positive end-expiratory pressure 12, 9, 6, 3, and 0 cm H2O. The imaging sequence was repeated after lung injury induced by whole-lung lavage and injurious ventilation in four rabbits. Cross-sections of the same individual airways were measured.Measurements and Main Results: The airways were measured at baseline (n = 48; radius, 1.7 to 0.21 mm) and after injury (n = 32). Closure was observed at 0 cm H2O in three of 48 airways (6.3%; radius, 0.350.08 mm at positive end-expiratory pressure 12) at baseline and five of 32 (15.6%; radius, 0.28 +/- 0.09 mm) airways after injury. Cross-section was significantly reduced at 3 and 0 cm H2O, after injury, with a significant relation between the relative change in cross-section and airway radius at 12 cm H2O in injured, but not in normal lung (R = 0.60; p < 0.001).Conclusions: Airway collapsibility increases in the injured lung with a significant dependence on airway caliber. We identify "compliant collapse" as the main mechanism of airway closure in initially patent airways, which can occur at more than one site in individual airways.
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- Porra, Liisa, et al.
(författare)
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Synchrotron Imaging Shows Effect of Ventilator Settings on Intrabreath Cyclic Changes in Pulmonary Blood Volume
- 2017
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Ingår i: American Journal of Respiratory Cell and Molecular Biology. - : AMER THORACIC SOC. - 1044-1549 .- 1535-4989. ; 57:4, s. 459-467
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Tidskriftsartikel (refereegranskat)abstract
- Despite the importance of dynamic changes in the regional distributions of gas and blood during the breathing cycle for lung function in the mechanically ventilated patient, no quantitative data on such cyclic changes are currently available. We used a novel gated synchrotron computed tomography imaging to quantitatively image regional lung gas volume (Vg), tissue density, and blood volume (Vb) in six anesthetized, paralyzed, and mechanically ventilated rabbits with normal lungs. Images were repeatedly collected during ventilation and steady-state inhalation of 50% xenon, or iodine infusion. Data were acquired in a dependent and nondependent image level, at zero end-expiratory pressure (ZEEP) and 9 cm H2O (positive end-expiratory pressure), and a tidal volume (V-T) of 6ml/kg(V(T)1) or 9ml/kg(V(T)2) at an Inspiratory: Expiratory ratio of 0.5 or 1.7 by applying an end-inspiratory pause. A video showing dynamic decreases in Vb during inspiration is presented. Vb decreased with positive end-expiratory pressure (P = 0.006; P = 0.036 versus V(T)1-ZEEP and V(T)2-ZEEP, respectively), and showed larger oscillations at the dependent image level, whereas a 45% increase in VT did not have a significant effect. End-inspiratory Vb minima were reduced by an end-inspiratory pause (P = 0.042, P = 0.006 at nondependent and dependent levels, respectively). Normalized regional Vg:Vb ratio increased upon inspiration. Our data demonstrate, for the first time, within-tidal cyclic variations in regional pulmonary Vb. The quantitative matching of regional Vg and Vb improved upon inspiration under ZEEP. Further study is underway to determine whether these phenomena affect intratidal gas exchange.
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