Emphysema may cause high pulmonary artery pressure. Pulmonary hypertension is caused by a variety of diseases of the heart, lungs, or pulmonary vasculature itself, and manifests itself as increased pressure and resistance in the pulmonary circulation, which can lead to increased right heart load, right heart insufficiency, and decreased pulmonary blood flow, resulting in a range of clinical manifestations. In severe emphysema, the alveoli are distended, and the interstitial walls of most alveoli rupture and fuse, forming large alveoli, with a consequent reduction in the capillary beds of the alveolar walls. The pressure within the emphysematous alveoli tends to increase, compressing the capillaries of the interalveolar wall and causing stenosis. In addition, emphysema patients, when the expiratory pressure within the alveoli can rise up to 40cmH2O, and due to the significant prolongation of the expiratory phase, resulting in the pulmonary artery blood can not be successfully perfused into the alveolar capillaries. All of the above are directly or indirectly caused by the reduction of the pulmonary vascular bed, resulting in increased pulmonary artery pressure.