Comparison of Single Breath Carbon Monoxide Diffusing Capacity and Pressure-Volume Curves in Detecting Emphysema

Abstract

To evaluate the sensitivity of diffusing capacity (DLCO) and pressure-volume (P-V) curves in the detection of emphysema, these tests were compared with pathologic assessment of emphysema in patients undergoing lung resection for a localized tumor, and with the overall extent of emphysema as assessed by computed tomography (CT). The resected lung specimens were fixed in the inflated state and cut at 1-cm intervals in the horizontal plane. The pathologic extent of emphysema was quantitated by comparison with a standard reference panel of emphysema grading. The overall extent of emphysema on CT was assessed by a visual scoring system in a total of 55 patients, 19 undergoing lung resection and 36 not undergoing lung resection. Analysis of 37 patients by pathology scores revealed 18 with no or trivial emphysema (emphysema grades .ltoreq. 5; mean grade, 2.2 .+-. SD 2.6) and 19 with emphysema (grades .gtoreq. 10; mean grade, 33.2 .+-. SD 24.2). Diffusing capacity, the ratio of DLCO to alveolar volume (DLCO/VA), maximal lung elastic recoil (PLmax), and lung elastic recoil at 90% of total lung capacity (PL90) were significantly different between the two groups, whereas K (the exponential constant describing the shape of the P-V curve) was not. The pathology grade of emphysema showed a significant correlation with (DLCO) (r = 0.53) and DLCO/Va (r = - 0.55), which was greater than the correlation with PLmax (r= -0.42) and PL90 (r = -0.43). There was no correlation between the pathology grade of emphysema and K. Using 95% confidence limits of predicted values to define abnormal lung function, we found DLCO to be the best predictor of emphysema. Correlation of pulmonary function tests with the overall extent of emphysema as assessed by CT gave similar results. We conclude that DLCO is a better indicator of macroscopic emphysema than are measurements from the P-V curve.