Figure 1.

Upper part: sections from low-dose, native chest CTs of both patients during expiratory hold with PEEP 10 cmH₂O, as well as during inspiratory hold (airway pressure 45 cmH₂O). Although both patients exhibited a distinct recruitability of the lungs, the underlying COVID-19 pattern explains the poor functional effect of higher PEEP levels in improving oxygenation. Lower part: this graph displays the volumes determined in the chest CTs (y-axis) per a range of 5 Hounsfield units (x-axis) at 10 cmH₂O (light grey) and 45 cmH₂O (black). Circles represent data from patient 1, triangles data from patient 2. The insert at the upper left shows the absolute lung volumes in liters classified as non-aerated, poorly aerated, normally aerated and overaerated again comparing the two pressures in both patients. Note the differences between the absolute lung volumes at both pressure levels (at 45 cmH₂O about 6.5 l for patient 1, about 4.5 l for patient 2).