FIGURE 1.

The effect of the prone position on alveolar size at functional residual capacity (FRC) and FRC plus tidal volume (VT). In the supine posture, at FRC, the most dependent alveoli are small because of higher pleural pressures, compression from the heart, and extrinsic compression from abdominal contents as compared with the prone posture. During tidal breathing, the distribution of local ventilation is more uniform in the prone posture because the alveolar volumes are more uniform at the initiation of each breath. This allows tidal volumes to be more evenly distributed throughout the lung, leading to less alveolar stress and lung injury. Figure reprinted with permission from Johnson NJ, Luks AM, Glenny RW. Gas Exchange in the prone posture. respir care. 2017 Aug;62(8):1097‐1110. PMID: 28559471