Relationship between quantitative CT metrics and pulmonary function in combined pulmonary fibrosis and emphysema

Combined pulmonary fibrosis and emphysema (CPFE) is increasingly recognized, as current reports of its clinical features show. To determine CPFE's physiologic and radiologic features, we conducted quantitative assessment of computed tomography scans to compare with those of chronic obstructive pulmonary disease (COPD).

In 23 patients with CPFE and 42 patients with COPD, we measured the extent of emphysema (LAA %), parenchymal density, and total cross-sectional areas of pulmonary vessels smaller than 5 mm(2) (%CSA <5) and 5-10 mm(2) (%CSA 5-10).

For CPFE, airflow was better, but diffusing capacity for carbon monoxide (DLCO) was worse than for COPD, whereas LAA % was similar for both groups. The %CSA <5 was greater but %CSA5-10 was less in CPFE than COPD. COPD involved a negative correlation between DLCO and LAA % at all lung sites; those factors correlated for CPFE only in the upper lobe (r = -0.535). In contrast, CPFE had a negative correlation between DLCO and parenchymal density in lower lobes (r = -0.453), but COPD showed no correlation in any such sections. In CPFE, no correlation was apparent between LAA in upper lobes and parenchymal density in lower lobes. The annual rate of FVC decline (-169.26 ml/year) in CPFE patients correlated with parenchymal density (r = -0.714).

In CPFE, fibrosis and emphysema apparently existed independently, but both correlate with and likely contribute to the disproportionate reduction in gas exchange. Our study also suggested that pulmonary fibrotic changes may be more important contributors than emphysema for disease progression.