To make it easier to understand breathlessness, it may help to understand the way lungs work.
We have two lungs – one on each side of the chest. When we breathe in, air passes from our nose or mouth through the windpipe (trachea), which divides into two tubes (airways), one going to each lung. These are known as the right and left bronchus. They divide to form smaller tubes called bronchioles, which carry air through the lungs.
At the end of the bronchioles, there are millions of tiny air sacs called alveoli. In the alveoli, oxygen is absorbed from the air we breathe in and passes into the bloodstream to be circulated around the body.
Carbon dioxide is a waste gas that needs to be removed from the body. It passes from the bloodstream into the alveoli and is then breathed out by the lungs.
Just below your lungs is a sheet of muscle called the diaphragm. The diaphragm and the muscles of the lower chest are the main breathing muscles used when you are relaxed.
During heavy exercise, the muscles in your shoulders and upper chest can also help with breathing. These muscles are not designed to work for long periods of time and tire easily.