Medically termed ‘dyspnoea’, this may be due to any condition which renders the blood deficient in oxygen, and which therefore produces excessive involuntary efforts to gain more air. Exercise is a natural cause, and acute anxiety may provoke breathlessness in otherwise healthy people. Deprivation of oxygen – for example, in a building fire – will also cause the victim to raise his or her breathing rate. Disorders of the lung may diminish the area available for breathing – for example, ASTHMA, PNEUMONIA, TUBERCULOSIS, EMPHYSEMA, BRONCHITIS, collections of fluid in the pleural cavities, and pressure caused by a TUMOUR or ANEURYSM.

• PLEURISY causes short, rapid breathing to avoid the pain of deep inspiration.

• Narrowing of the air passages may produce sudden and alarming attacks of difficult breathing, especially among children – for example, in CROUP and ASTHMA.

• Most cardiac disorders (see HEART, DISEASES OF) cause breathlessness, especially when the person undergoes any special exertion.

• Severe ANAEMIA is a frequent cause.

• Obesity is often associated with shortness of breath.

Mountain climbing may cause breathlessness because, as altitude increases, the amount of oxygen in the air falls (see ALTITUDE SICKNESS). (See also LUNGS and RESPIRATION.)