Emphysema affects the distal bronchioles and causes occlusions of the peripheral alveolar vessels, thereby resulting in reduced capillary blood flow and a reduction in the alveolar capillary surface area available for gas exchange.[42] Although our meta-analysis results initial revealed that the 8 types of vasodilator drugs had no significant effect on DLCO, which may be due to the different mechanisms of action of the drugs, subgroup analysis showed that PDE-5 inhibitors could effectively improve DLCO indicating the therapeutic potential of PDE-5 inhibitors for COPD. Here, PDE5A is linked to pulmonary emphysema.