Efficacy of prone position in acute respiratory distress syndrome patients: A pathophysiology-based review

Figure 1 Relationship between gravity, superimposed pressure and shape matching. A: In supine position gravity, superimposed pressure, and shape matching act to the same detrimental direction; B: In prone position, shape matching counterbalances gravity and superimposed pressure allowing a more homogeneous inflation of the dependent lung areas.

Figure 2 A summary showing the sequential effects of prone position on acute respiratory distress syndrome diseased lung. A: Original shape of the isolated lung; the dorsal side is bigger than the ventral one (no gravity); B: The result of shape matching: alveolar units have bigger size ventrally and smaller size dorsally (no gravity); C: The additive effect of gravity on ventilation and perfusion: blood flow is being diverted toward dependent regions, while dependent pulmonary units close; D: Immediately after turning to the prone position, pulmonary blood flow in dorsal regions of the lung is maintained unmodified; E: Dorsal lung recruitment follows (greater than ventral de-recruitment), gravitational forces compress the ventral region, but this effect is damped by regional expansion due to shape matching; F: Transpulmonary pressure and regional inflation distribution become more homogeneous throughout the lung resulting finally to better oxygenation.

Figure 3 Prone positioning allows the heart to lay on the sternum and the compressive force of the heart on dorsal lung regions to be eliminated.