Mechanical dissociation of bronchi from parenchymna in the immature pigletlung

Previous studies of isolated piglet lungs suggested that local distending f orces around bronchi might be relatively weak before postnatal growth and m aturation. The present study used tantalum bronchograms to compare pressure -diameter relationships of bronchi in situ and after excision from the pare nchyma in immature (3- to 7-day-old) and mature (3-mo-old) piglets. The mat ure group reproduced behavior that is well established in mature lungs from other species; i.e., bronchial diameters maintained a constant relationshi p to the parenchyma as the lungs were deflated from maximum to minimum volu me. In sharp contrast, diameters failed to change until the immature lungs were deflated to (5 cmH(2)O transpulmonary pressure. Total pet-cent change in bronchial diameter was then only 24% in the immature lungs compared with 47% in the mature lungs (P < 0.002). Total elastances of mature generation 3-8 bronchi did not change when they were excised from the parenchyma. How ever, in the same generations of immature bronchi, total elastances were lo wer after than before (1.06 vs. 1.60 cmH(2)O/%, P < 0.05) excision from the parenchyma. Elastances of the excised immature and mature bronchi were the n the same (1.06 vs. 1.03 cmH(2)O/%, not significant). Because elastic modu li of the lung parenchyma are also similar in the two age groups, it was co ncluded that local features of airway-parenchyma coupling limited the gener ation of local parenchymal recoil around bronchi in the immature lungs.