Breathlessness

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Breathlessness is the feeling of being out of breath. This is normal in healthy people who exert themselves physically, but can be a sign of illness if it occurs at a much lower level of exertion than expected.

The basis behind breathlessness is a balance. On the one hand, there is the bodyâ€™s need for oxygen and its supply from the lungs. On the other hand, there is the level of waste gas (carbon dioxide, or CO2) that builds up in the body during exercise. Muscles working hard in exercise need more oxygen, and produce more CO2. Special cells in the main arteries detect the levels of oxygen and CO2, and these send signals to the brain and heart to increase breathing and pulse rates. This means that more blood is pumped around the body, picking up more CO2 from the muscles, to be released in the lungs to be breathed out, and picking up more oxygen there to deliver to the muscles.

In a healthy person, physical fitness will set the level when breathlessness is experienced. The more regular physical exercise a body is used to, the more efficient the muscles are. They use oxygen better and create less CO2, and the lungs and heart are more efficient, too. This is why a fit person can do more exercise without getting breathless than an unfit person can.

Certain illnesses can mimic the effects of unfitness, but at much lower levels of exertion than simple exercise, so that even crossing a room slowly can be a major effort. Breathlessness is said to be acute if it happens suddenly and severely, and chronic when it has built up gradually over a long time. The causes of these two types are generally different.