The 'Destructive Index' in nonemphysematous and emphysematous lungs. Morphologic observations and correlation with function

We examined the relationship of the newly described 'Destructive Index' (DI) to emphysema using nine nonemphysematous and 13 emphysematous lungs obtained at autopsy. The amount of emphysema was assessed by the panel method (emphysema grade, EG) and measurement of the mean linear intercept (Lm). The DI depends on three components - alveolar wall/duct disruption, DI(d); alveolar fibrosis, DI(f); and classic emphysema, DI(e). DI(f) was a minor component in our series. The mean DI was 5.8 ± 2.5, 10.9 ± 3.9, and 55.7 ± 7.0% (± 1 SEM) in the nonemphysematous (panel grade EG = 0), mild (0 < EG ≤ 25), and moderate to severe (30 ≤ EG ≤ 60) emphysematous lungs, respectively. The increase in the DI in mild emphysema did not reach significant levels (p < 0.2). The mean DI(d) was 5.6 ± 2.5, 10.0 ± 4.0, and 12.8 ± 3.9% in the above categories, and the DI(d) in mild emphysema did not differ significantly from that of the nonemphysematous lungs. Lm showed a similar trend and alveolar disruption did not precede airspace enlargement, rather both changes appeared to advance in parallel. The DI correlated closely with EG (r = 0.83, p < 0.01), but this was due to the component of DI(e). The DI(e) increased steeply in the lungs with EG ≥ 30. The DI correlated with post-mortem function tests such as the volume of the air in the lung at a transpulmonary pressure of 30 cm H₂O (V₃₀), lung recoil pressure at 90% of V₃₀, and the shape constant K, calculated from fitting a single exponential to volume-pressure curves (p < 0.05). Slightly less residual variance was found between recoil pressure of 90% of V₃₀ and DI compared to EG and Lm, and K was only significantly related to DI. DI(d) in apparently nonemphysematous parts of emphysematous lungs (DI'(d)) was increased but not significantly in mildly emphysematous lungs but was increased significantly in moderately and severely emphysematous lungs. We conclude that DI was not of increased value in assessing emphysema in our cases and takes considerably more time than conventional measurements of emphysema. DI'(d) could not account for previously reported loss of recoil and increased lung volumes in mildly emphysematous lungs.