MODEL RELEASED. Oxygen therapy. View of a general practice doctor holding an oxygen mask up to an elderly man's face. The patient is suffering from breathlessness due to bronchitis, asthma, angina pectoris or a heart attack (myocardial infarct- ion). The oxygen mask supplies him with air enriched with the oxygen he is lacking. The doctor is also examining his chest with a stethoscope. Asthma and bronchitis occur due to inflammation of the lung's airways. Angina is a feeling of pain and constriction in the chest. It results from a blockage in one of the coronary arteries which supply the surface of the heart with oxygen. This can cause tissue death and a heart attack.