Fig. 1.

Quantitative CT analysis. The figure shows how the CT number of 9 schematic voxels may inform the changes of aeration that the lungs undergo during ARDS and in response to ventilatory management. Panel 1 shows 9 normally inflated voxels (blue, CT number between − 900 and − 501 HU). Once ARDS occurs (panel 2), a number of voxels become poorly inflated (n = 2, yellow, CT between − 500 and − 101 HU) and non-inflated (n = 3, green, CT number between − 100 and 100 HU) despite the application of 5 cmH₂O of PEEP. When PEEP is increased to 10 cmH₂O (panel 3), a poorly inflated voxel is restored to normal inflation, but a normally inflated voxel becomes hyperinflated (n = 1, red, CT number below − 901 HU). During tidal ventilation (panel 4), voxels pass from normal inflation to hyperinflation (tidal hyperinflation), while others are passing from non-inflation to normal inflation (tidal opening and closing, or atelectrauma). ARDS acute respiratory distress syndrome, CT computed tomography, HU Hounsfield unit, PEEP positive end-expiratory pressure