Lung disease. X-ray of the chest of a patient with chronic obstructive pulmonary disease (COPD). This is a collection of diseases that includes emphysema and chronic bronchitis. The damage to the lung tissue reduces gas exchange in the lungs. This leads to shortness of breath, which can develop into a serious lack of oxygen in the blood and cyanosis (blue colouring), or even respiratory and heart failure. The main cause is cigarette smoking.