| Parameter | Group | |||
| Saline/sham | Saline/ATRA | Elastase/sham | Elastase/ATRA | |
| Body weight g | 359±14 | 358±25 | 343±31 | 342±22 |
| VRL cm3 | 6.0±0.6 | 6.2±0.6 | 8.5±1.4 | 7.9±0.7 |
| Mass-spec. VRL mm3·g−1 | 16.7±1.4 | 17.4±0.9 | 24.8±3.3 | 23.8±2.4 |
| Mass-spec. Vair mm3·g−1 | 11.8±1.1 | 12.7±1.0 | 19.9±2.5 | 18.0±2.1 |
| Mass-spec. Vast mm3·g−1 | 2.7±0.3 | 2.5±0.4 | 2.8±0.7 | 3.8±0.4* |
| Mass-spec. Sa cm2·g−1 | 12.7±1.5 | 12.2±1.4 | 9.6±1.7 | 10.4±1.3 |
| SsAEII cm2·cm−2 | 2.7±0.6 | 3.0±0.4 | 2.8±0.7 | 1.8±0.6* |
| τast μm | 2.1±0.2 | 2.1±0.2 | 2.9±0.3 | 3.7±0.1* |
| MCL μm | 73.0±6.0 | 69.3±5.6 | 91.3±7.6 | 80.6±4.2* |
Data are presented as mean±sd. ATRA: all-trans retinoic acid; VRL: volume of fixed right lung; mass-spec.: mass-specific; Vair: volume of distal airspaces; Vast: volume of alveolar septal tissues; Sa: surface area of alveolar septa; SsAEII: fraction of alveolar surface area occupied by alveolar epithelial type II cells; τast: arithmetic mean thickness of alveolar septa; MCL: mean chord length of acinar airspace (alveoli and alveolar ducts). If normality and equal variance were given at p>0.1, the unpaired t-test was used to test for significant differences between saline/sham (SS) versus saline/ATRA and elastase/sham (ES) versus elastase/ATRA, respectively; otherwise non-parametric Mann–Whitney U-test was performed. *: p<0.05 versus group ES.