LAUSR

Introduction The mechanism by which prone position (PP) reduces mortality in moderate-to-severe acute respiratory distress syndrome (ARDS) patients as compared to supine (SP) [1] likely includes reduction/homogenization of lung stress/strain. The common accepted scenario is that this effect stems from an increase in chest wall elastance (Est,cw) in PP. However, whether, and to what extent, the angulation of the body may affect Est,cw is unclear. Our hypothesis is that thorax inclination significantly changes respiratory system mechanics and lung volume from SP to PP, as previously suggested in healthy humans [2] and anesthetized patients [3].