Asthmatics breathe on average about twice as much air as they should. The normal breathing rate is four to six liters of air per minute, whereas asthmatics breathe at a rate in excess of this - breathing 10 - 14 liters per minute at rest. This is known as hyperventilation (HV) which simply means to overbreathe, either by breathing too quickly or too deeply, usually through the mouth.

This long-term hyperventilation upsets the vital balance of respiration. It seems logical that if you breathe more, then you should absorb more oxygen, which the body needs. In reality you don't absorb more oxygen. 

An adequate level of carbon dioxide is vital for oxygenation because it controls the acid/alkali balance (pH) of the blood. When carbon dioxide levels start to drop, this leads to a condition known as respiratory alkalosis. The "stickiness" of hemoglobin for oxygen increases, resulting in less oxygen being released where it is needed.

To counteract the alkalosis, cells begin to produce lactic acid which leads to tired, aching muscles and exhaustion. If you have had asthma for 2 or 3 days, you will have sore muscles particularly in your chest, shoulders and back.

This loss of carbon dioxide from the blood stream also tightens the smooth muscle wrapped around the airways, giving the "tight chest" feeling associated with asthma.

Low levels of carbon dioxide cause the mast cells to release histamine resulting in inflammation which narrows the airways further.

Hyperventilation cools and dries out the airways making them sensitive and the mucus glands produce more mucus to moisten them. This increased mucus and inflammation results in coughing, wheezing, a blocked or running nose. If hyperventilation continues, the mucus dries out and becomes sticky, causing you to cough or wheeze even more.

It is a vicious cycle to break.