Influence of abdomen on respiratory mechanics in supine rabbits

Previous studies showed that abdominal evisceration has no effect on respiratory system compliance. We hypothesized that this could be related to lung distortion in eviscerated animals. Methods were developed for continuous recording of pleural pressure (Ppl) at various sites over the costal (co) and diaphragmatic lung surface (di) in acutely and chronically instrumented rabbits. We compared Delta Ppl,co and Delta Ppl,di recorded at mid-lung height during inflations in anesthetized, paralyzed supine rabbits before and after evisceration. Cranial and caudal Delta Ppl,co were the same under all conditions. In intact animals, Delta Ppl,co and Delta Ppl,di were equal at all inflation volumes, whilst in eviscerated animals, Delta Ppl,di were smaller than Delta Ppl,co, the difference increasing with lung inflation. At any given volume? rib cage circumference (Crc) was smaller after evisceration, but the Crc-Delta Ppl,co relationship remained unchanged. These results are indicative of non-uniform lung expansion after evisceration and are consistent with model predictions based on cylindrical deformation and lung stress-strain relationship. This deformation should mimic the effect of a reduced lung compliance, keeping respiratory system compliance of eviscerated animals nearly normal. Similar deformation should have occurred also in intact rabbits during strong inspiratory efforts and in the erect posture, because lower Ppl,di than Ppl,co values were observed at the same lung height under these conditions. (C) 1999 Elsevier Science B.V. All rights reserved.