eFigure 25-12.

Correlation between diffusing capacity for carbon monoxide (Dl_CO) and emphysema grade.

Top, The single-breath Dl_CO, expressed as the log of the percentage of predicted normal, is displayed on the ordinate. Emphysema grade is displayed on the abscissa and was determined by the panel grading method on lung tissue resected from these patients within 1 week of pulmonary function testing. The solid line is the line of best fit (r = −0.73), the outer dashed lines show the 95% confidence limits for the points, and the inner dashed lines show the 95% confidence limits for the line. The single-breath Dl_CO correlates with the presence and amount of emphysema except when emphysema is mild (grades 0 to 30); when single-breath Dl_CO was plotted against emphysema for patients with minimal disease (grades 0 to 30), there was no significant correlation. Bottom, The intrabreath Dl_CO, expressed as the log of the percentage of predicted normal at 50% exhaled vital capacity, is displayed on the ordinate. Emphysema grade is displayed on the abscissa and was determined by the panel grading method on lung tissue resected from these patients within 1 week of pulmonary function testing. The solid line is the line of best fit (r = −0.77), the outer dashed lines show the 95% confidence limits for the points, and the inner dashed lines show the 95% confidence limits for the line. Thus the intrabreath Dl_CO correlates with the presence and amount of emphysema even when emphysema is mild (grades 0 to 30) and cannot be detected or quantified by the single-breath method.