Sputum MMP-9 expression levels correlated negatively with post-bronchodilator FEV1% predicted [r = −0.530, (95% CI −0.686, -0.327), p < 0.001], post-bronchodilator FEV1/FVC [(r = −0.551 (−0.701, -0.354], p < 0.001], and DLco [r = −0.399 (−0.539, -0.102), p = 0.048], (Figure 2) but were not significantly associated with the CT extent of emphysema [r = 0.266 (−0.020, 0.446), p = 0.115]. Here, MMP9 is linked to pulmonary emphysema.