Fig. 1

Individual morphological response to prone positioning. Fifteen mechanically-ventilated patients with COVID-19 underwent a lung computed tomography in the supine and prone position. A–D we describe the individual changes in the total (tissue and gas) volume of the non-aerated (density above − 100 HU), poorly-aerated (from − 100 to − 500 HU), normally-aerated (from − 500 to − 900 HU), and over-aerated (below − 900 HU) compartments with prone positioning, in descending order. E, F each CT slice was divided into ten equal vertical levels, from the sternum (vertical level 1) to the vertebra (vertical level 10), and in ten equal horizontal levels, from the apex (horizontal level 1) to the base (horizontal level 10) of the lung. Herein we describe the individual change in the degree of heterogeneous aeration along the vertical and horizontal axis, expressed with the standardized median absolute deviation of regional gas-to-tissue ratios, and presented in descending order. Negative values indicate that the volume of a given compartment or the degree of heterogeneity decreased with prone positioning. Each bar refers to one patient. The same letter in the six panels refers to the same patient. Patient N had a baseline PaO₂:FiO₂ of 273 mmHg; the decision to prone him was based on the detection of large ventral lung hyperinflation at the CT taken in the supine position (please refer to the main text for other details)