PNMT and chronic obstructive pulmonary disease: Bioinformatic analysis identified six critical markers (CYP1B1, CA3, AHRR, MGAM, PNMT, and PLA2G1B) that regulated CEM in the progression of COPD, from which a prognostic model was constructed using a nomogram with an area under the curve (AUC) of 0.814.