Internal surface area and other measurements in emphysema

Some measurements of emphysema were made on 29 pairs of non-emphysematous lungs and 44 pairs of emphysematous lungs inflated at a standard transpulmonary pressure of 25 cm. of formalin. These were: a subjective visual assessment (units); an assessment of the volume of the lung parenchyma involved by emphysema (point count); an average subjective visual grading by eight pathologists (Co-op score); mean linear intercept or average distance between alveolar walls at a transpulmonary pressure of 25 cm. of formalin (Lm); mean linear intercept corrected to total lung capacity (Lm_C); internal (alveolar) surface area at 25 cm. transpulmonary pressure (ISA); internal surface area at total lung capacity (ISA_C); internal surface area corrected to an arbitrary lung volume of 5 litres (ISA₅). Internal surface area measurements were generally decreased in severe emphysema. Because of the wide range of ISA and ISA_C in non-emphysematous lungs, most emphysematous lungs fell within the normal range. The range of ISA₅ was smaller in non-emphysematous lungs and most emphysematous lungs fell outside this range. ISA₅ in `mild' emphysema was not distinguishable from non-emphysematous lungs. Most emphysematous lungs in which the surface area was decreased less than expected from subjective assessment were examples of centrilobular emphysema. Lm and Lm<sub>C</sub> were increased in emphysema. ISA<sub>5</sub>, Lm, and Lm<sub>C</sub> paralleled the subjective assessments of emphysema rather better than ISA or ISA<sub>C</sub>, even when the latter were expressed as a percentage of predicted. Lm and Lm<sub>C</sub> in lungs with mild emphysema fell within the ranges found in non-emphysematous lungs, but the mean value of Lm in lungs with `mild' emphysema was different from the mean Lm of non-emphysematous lungs, at conventional levels of significance. Since objective methods did not recognize adequately examples of `mild' emphysema, a subjective visual grading system (with its limitations) may have a definite place.