How does emphysema reduce the amount of oxygen which diffuses into the blood?

See below: In emphysema, the alveoli are destroyed and that is the place where the exchange of oxygen and carbon dioxide is supposed to occur. Malfunctioning alveoli prevent this exchange by not allowing the red blood cels to have contact with the air we breathe so the gas exchange may take place.

From Destruction: The destruction in the lung tissue from emphysema makes the oxygen harder to cross into the blood because there is less tissue surface left. With less air sacs to participate in gas exchange, it is harder for oxygen to cross into the blood. Does that make sense? That's why people should stop smoking.

Destroys the lung: Emphysema causes destruction of lung tissue. The blood vessles in the lung get destroyed in the lung. These vessles carry the blood in the lung to pick up oxygen. If they are destroyed then, oxygen can not get into the blood vessles / blood and you get low oxygen.

Destruction of lung: Emphysema is the destruction of lung tissue, most often from smoking. When this happens, the amount of lung available to participate in the exchange of oxygen decreases, which makes it harder for oxygen to get into the blood from the air. Thus, some patients with emphysema have low oxygen levels.