Mechanical forces contribute to neonatal lung growth: the influence of altered diaphragm function in piglets

Neonatal lung growth is controlled in part by mechanical forces. Altered mechanical forces precipitated by phrenectomy or prosthetic replacement of the diaphragm result in altered thoracic volume relationships, which, in turn, change lung distending pressures and or thoracic volume. These effects might contribute to regional lung growth. We postulated a relationship between altered thoracic mechanical forces and changes in lung growth and asked if altered diaphragm function influenced regional lung growth. Piglets (28d, 7-8kg), were assigned to left transthoracic phrenectomy (P), prosthetic diaphragm replacement (PDR), or sham (S), (n = 6). After a mean 10 days, piglets were studied with tracheostomy and regional pleural pressure transducers. Integrated lung volumes (LV) were recorded with intrapleural pressure (Pip). Dynamic compliance (Cdyn) was calculated (dV/dP). After sacrifice continuous pressure volume (P/V) curves were generated. Lungs were then cut into 4 quadrants based on relationship to R/L bronchus and processed for DNA content and total protein indexes. Analysis of data were made within and between groups. Body weight and gain were similar in all. LV, Pip, Cdyn, and P/V were not significantly different in PDR and P compared with S. Pip differences between thoracic regions within each group were significant for PDR and showed LU less than RU, LL less than RL (P less than 0.05). RU and RL Pip in the PDR group were the same as S. Pip in the P group were decreased in the RU, LU, and LL but only the LL approached significance. Whole lung wet weights were decreased (P less than .05) in P compared to PDR and S.(ABSTRACT TRUNCATED AT 250 WORDS)