Measurements of regional strain and time constants in ex-vivo animal models at different PEEP levels using functional respiratory imaging (FRI)

Aims and objectives: In ARDS, lung units are characterized by large heterogeneities of distension and variations in resistance and compliance. Regional heterogeneity in time constant (τ) values may have meaningful consequences in injured lung during ventilation by creating regional differences of strain (e), or zones of high shear stress and shear strain between lung regions. In this study, we hypothesized that FRI can be used to assess regional values of e and inspiratory τ (τI) and the influence of positive end expiratory pressure (PEEP) on these parameters. Methods: Ex-vivo lungs of five adult female Yorkshire pigs were ventilated with a PEEP of 0, 5 and 10cmH2O during CT scans. Three-dimensional reconstructions of the airways (see figure 1), the right and left anterior lobes (RAL and LAL), right and left caudal lobes (RCL and LCL), right and left diaphragmatic lobes (RDL and LDL) and right internal lobe (RIL) at full inspiration and expiration were created. Using FRI, lobar e and τI values were calculated at the different PEEP levels. Results: Strain decreased linearly with increasing PEEP (p=0.001). RAL was found to have the lowest e while no differences were observed between the other lobes. The τI decreased quadratically in a concave pattern with increasing PEEP (p Conclusions: FRI can be used to assess global and regional values of e and τI. The manipulation of PEEP causes changes in regional e that are reflected by changes in τI values.