The key to this conundrum was the discovery that oxygen deficiency is not caused by a lack of oxygen, but by a lack of carbon dioxide! The concentration of carbon dioxide in the blood affects its pH (acidity/alkalinity) and the strength with which oxygen binds to haemoglobin (oxyhaemoglobin). Too little carbon dioxide (an acidic gas) results in higher blood pH (more alkaline), which inhibits the release of oxygen from oxyhaemoglobin in the tissues. The need for more oxygen results in increased breathing (hyperventilation) which flushes out more carbon dioxide from the lungs which in turn raises blood pH producing a vicious circle resulting in an asthma attack! In addition to this, carbon dioxide is a natural broncho-dilator, helping to keep the airways open. A lack of carbon dioxide results in the airways closing with dire consequences for an asthmatic!