Fig. 1. Model of a fluid-filled container with two flexible walls ( A, left ). Depending on the characteristics of the fluid and the container, an inflection point will develop along the vertical flexible wall, above which pressure will be negative and below which fluid pressure is increasingly positive. In A, right , the resultant shapes of diaphragm and abdomen reflect the balance of forces across these structures in an upright posture. ( B ) Supine, the “flexible walls” change orientation with respect to gravity. Below the anterior abdominal wall, pressure is now positive or negative, depending on body habitus, whereas pressure against the diaphragm steadily increases toward the vertebral column. Question: What impact will anesthesia/paralysis have in a system with such an inhomogeneous distribution of forces across the diaphragm?