MMP9 and chronic obstructive pulmonary disease: The excessive increase of TIMP-1 relative to MMP-9 eventually leads to excessive deposition of extracellular matrix in the airway, which promotes the occurrence and development of airway remodeling.15 Exhaled MMP-9 and TIMP-1 were significantly increased in the stable phase of COPD, and the concentration in the acute exacerbation period was further increased and negatively correlated with arterial blood gas parameters.16