Fig. 3

Regional lung gas-to-tissue ratio in the supine and prone position. Fifteen mechanically-ventilated patients with COVID-19 underwent a lung computed tomography (CT) in supine and prone positions. 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 ratio of the gas volume (ml) to the tissue weight (g) in each of those levels, in the supine and prone positions. Data are reported as median (Q1–Q3). A vertical gradient of lung inflation. On average, the gas-to-tissue ratio decreased by 0.34 (0.25–0.49) ml/g per level in the supine position and by 0.03 (− 0.11 to 0.14) ml/g in the prone position (p < 0.001). B horizontal gradient of lung inflation. On average, the gas-to-tissue ratio decreased by 0.14 (0.04–0.27) ml/g per level in the supine position and by 0.11 (− 0.05 to 0.21) ml/g in the prone position (p = 0.003)