Difficulty in breathing enough air.
Breathlessness, or dyspnoea, 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.
Experiencing a sensation of strained respiration, commonly known as labored breathing, can occur under certain circumstances. Breathlessness is a natural response to physical activity or exertion, but it can also manifest as a symptom of certain underlying medical conditions.