Effect of increased acceleration on regional pleural pressure in dogs

The variation of pleural pressure was measured in anesthetized spontaneously breathing dogs subjected to increased acceleration (0-4 G) in a centrifuge. Two groups of animals were studied. In one group, the resultant acceleration was in a direction either ventral-to-dorsal (+Gx) or dorsal-to-ventral (-Gx), with a relatively small residual cranial-to-caudal acceleration. In the other group, the resultant acceleration was either cranial-to-caudal (+Gz) or caudal-to-cranial (-Gz), with a relatively small residual dorsal-to-ventral acceleration. Pleural liquid pressure (Ppl) was measured by two rib capsules that were separated by 7-9 cm and oriented either in the dorsal-to-ventral or cranial-to-caudal direction. At functional residual capacity, Ppl in the nondependent lung region became more negative when the acceleration was in the +Gx or +Gz direction. Thus the lung would be susceptible to damage that results from overexpansion in these acceleration directions. By contrast, acceleration in the -Gx or -Gz direction produced values of Ppl at functional residual capacity that were positive. Thus, in these acceleration directions, the respiratory muscles must provide greater force during inspiration to overcome lung compression before lung ventilation can occur. The Ppl gradients with respect to the acceleration directions increased approximately in proportion to acceleration in the +Gx, -Gx, and -Gz directions but remained relatively constant in the +Gz direction.