Shortness of breath (SOB) or the perceived inability to get enough air is caused by a number of factors, including lung and heart disease. 

For people with obstructive lung disease (COPD), usually reflects the fact that the air is trapped in the lungs and not properly exhaled. CO2 builds up and the body feels short of breath. Breathing techniques like purse lip breathing help move more air out of the lung and therefore more O2 into the lungs. This alleviates the shortness of breath.

One of the other causes of shortness of breath is heart disease. Congestive Heart Failure (the inability of the heart muscle to pump blood) and heart value failure are two reasons for vascular based SOB. If a person is SOB and has edema or swelling of the lower extremities, they may have a heart problem and not a lung problem

www.onebreath.info