Vascular resistance refers to the resistance to the flow of blood in the vascular system, causing increased pulmonary vascular resistance mainly due to the following factors: 1, long-term recurrent chronic bronchitis and peribronchitis, which can involve the adjacent small pulmonary arteries causing vasculitis, luminal wall thickening, luminal narrowing or fibrosis or even complete occlusion, resulting in increased pulmonary vascular resistance to produce pulmonary hypertension; 2, with the aggravation of emphysema, alveolar pressure increases compression alveolar capillaries, resulting in narrowing or occlusion of the capillary lumen; 3, alveolar wall rupture resulting in destruction of the capillary network, alveolar capillary bed impairment of at least more than 70%, increased pulmonary circulation resistance, prompting the occurrence of pulmonary hypertension; 4, pulmonary vasoconstriction and pulmonary vascular remodeling, chronic hypoxia causes vasoconstriction tubular wall tension increases, can directly stimulate the wall hyperplasia, pulmonary fine arteries and malformed microarteries of smooth muscle Cell hypertrophy or atrophy, increased intercellular matrix, intimal elastic fibers and collagen fibers proliferation, non-malformed micro-artery mechanization to thicken the vessel wall, sclerosis, lumen narrowing, increased resistance to blood flow.