Narrowing/distortion of airways
Chronic Bronchitis
Emphysema
Asthma
COPD
Bronchiectasis
obstruction by tumor or foreign body
pnumonia
Pulmonary infarction
pleural effusion
primarily affects perfusion
Pulmonary embolism
Enlarged lymph nodes (causing compression of vessels)
Vasculitis or multiple small pulmonary emboli