Late-gestation tracheal occlusion in the fetal lamb causes rapid lung growth with type II cell preservation

Background. Fetal tracheal occlusion (TO) results in varying degrees of lun g growth. This study examines whether gestational age influences lung growt h response following TO. Materials and methods. Fetal lambs (term = 145 days) underwent TO early (10 8 days, n = 6) or late (122 days, n = 6) in gestation. Aspirated lung fluid volume (LFV) and intratracheal pressure (ITP) were recorded daily. Two wee ks after TO, the fetuses were sacrificed. Lung growth was assessed by lung weight and stereologic volumetry. Type II cellular density was assessed by computer-assisted morphometry using antisurfactant protein B antibody. Results. After early TO, ITP remained below 2 mm Hg for all but one of the first 5 days. In late TO, ITP rose to 4.8 +/- 1.7 mm Hg by Day 1 and remain ed elevated. LFV remained lower after early than after late TO (P < 0.05) f or 8 days. Thereafter, pressure and volume reached similar levels in both T O groups; both were significantly higher than their respective controls (P < 0.05). Parenchymal fraction (1 - air-space fraction) was significantly sm aller after late TO (22.8 +/- 1.2%) than after early TO (31.3 +/- 0.5%). Ty pe II density was 38.0 +/- 12.4 x 10(6)/mL after early TO and 84.0 +/- 24.3 x 10(6)/mL in control (P < 0.05); the difference between late TO and contr ol was not significant. Conclusions. Late tracheal occlusion in fetal lambs caused more rapid lung growth than earlier TO, although ultimate lung size was similar in both gro ups. Late TO also resulted in greater air-space fraction and better preserv ation of the type II cell population than fore be preferable to prolonged o cclusion initiated earlier. (C) 2000 Academic Press.