Effect of gravitational and inertial forces on pleural and esophageal pressures

Abstract

Seven dogs were exposed to forward, backward, and right and left lateral accelerations for 60 sec. at mean levels of 2.1, 4.3, and 6.7 G. Intrapleural pressures at dorsal (paravertebral), ventral (retrosternal), left, and right sites plus esophageal pressure were measured by saline-filled catheters and P23D Statham gauges. With increasing acceleration, end-expiratory pleural pressures decreased at sites which, depending on body position, were superior in the thorax and increased at sites which were dependent. Esophageal pressures exceeded pleural pressures interpolated to the same level during all conditions studied. Interpolation of pleural and esophageal pressures to 0 G gave -5.5 and -2.7 cm H2O, respectively, independent of body position and site of measurement. It is concluded that differences in pleural pressure recorded at different sites in the thorax are caused by the weight of the thoracic contents and that the resulting pressure imbalances impose a limitation on the levels and durations of acceleration that can be tolerated with safety by animals and man when a given depth of lung is oriented in the direction of the resultant vector of acceleration.