#ARDS #FOAMed A comparison of some physiological effects of supine (left) and prone (right) positioning. In the prone position, reduced force from other organs is applied to the lungs, which allows for improved lung compliance and therefore improved relation between ventilation and perfusion of the lungs. Top panel: Dark blue arrows indicate the direction of the force exerted on the lungs by the heart. Middle panel: Arrows indicate the direction of the force exerted on the lungs by the abdominal organs. For prone positioning, less force from these organs is applied to the lungs, which allows for improved lung compliance by decreasing the force it needs to expand against. Bottom panel: Graded shading represents lung perfusion with darker shade representing greater ventilation/perfusion mismatch owing to alveolar collapse posteriorly in the supine position (reduced in the prone patient as this position allows for more even chest expansion). Note: A = anterior, P = posterior. Figure from: CMAJ November 23, 2020 192 (47) E1532-E1537