Topography of pleural surface pressure during simulation of gravity effect on abdomen

Abstract

When the abdominal pressure in supine rabbits and dogs was decreased until the lung volume equalled that in the head-up posture at FRC, a cranio-caudal gradient of transpulmonary pressure similar to that in the head-up posture at FRC was produced. By further lowering the abdominal pressure the gradient became greater than that in the head-up posture at FRC. When the abdominal pressure in head-down rabbits was decreased until the lung volume equalled that in the head-up posture at FRC the vertical gradient of transpulmonary pressure reversed and became nearly equal to that in the head-up posture at FRC. When the abdominal pressure in head-up rabbits was increased until the lung volume equalled that in the head-down posture at FRC the vertical gradient disappeared: it reversed only in exsanguinated rabbits. These results show that, except when the lung is engorged with blood, the distribution of transpulmonary pressure depends essentially upon the shape of the chest wall, which is mainly related to the gravity effect on its parts.