How does pleural effusion affect the function of the lungs?

The main effect of pleural effusion is its effect on the lungs. If the pleural effusion becomes large enough, it prevents the lung from properly expanding when breathing. This may lead to the shortness of breath and chest pain symptoms. Additionally, blood vessels deliver oxygen to and remove carbon dioxide from the small air sacs in the lung. Overtime with inadequate lung expansion some of the small air sacs may not open and this may result in poor delivery of oxygen to the blood vessels. This is referred to as ventilation perfusion mismatching.