Regional dynamic lung strain and specific elastance imaged by synchrotron computed tomography

Rationale: Artificial ventilation induces mechanical stresses that are potentially injurious to the lung tissue. We describe a new technique to quantitatively image regional lung strain and specific elastance that uses radiation generated by a synchrotron source. Methods: We used K-edge subtraction synchrotron CT during the washin of stable Xe, in 3 healthy anaesthetized rabbits in 2 axial image levels, to image regional specific ventilation (sV9) at a PEEP of 0 (ZEEP) and 9 cmH 2 O. Dynamic Strain within a given image voxel was computed based on sV9; as the percent tidal volume change per voxel gas volume. Specific elastance was given by : (Plateau pressure – end expiratory pressure) / Strain. Results: While mean dynamic strain significantly decreased with PEEP (14.8±4.6 vs. 17.3±7.7, p=0.001), specific elastance increased (1.63±0.23 vs. 0.67±0.21, p=0.002). High specific-elastance regions with poor ventilation in one animal on ZEEP were reversed with PEEP (Figure). Conclusions: Our data demonstrate the feasibility of imaging regional dynamic strain and specific elastance, using synchrotron imaging. This method can be useful for exploring the consequences of changes in mechanical ventilation settings on regional lung function in preclinical models of disease.