How Asthmatics Breathe
When we breathe in, our airways are pulled open as the chest wall gets larger, but when we breathe out, the airways tend to collapse, trapping air in the chest. If you are an asthmatic, emptying the lungs takes a long time because your airways are narrowed. You cannot completely empty the lungs before you have to take another breath. The more short of breath you are, the faster you try to breathe and the less time there is to exhale. The result of this is that the lungs retain, or "trap," a lot of air. This is called air-trapping, or hyperinflation. This process makes it harder to take another breath in, and your breathing muscles have to work harder to take in any air. A young or otherwise healthy asthmatic can usually overcome this difficulty, but at the cost of significant strain on the breathing muscles. If this demand is sustained too long, for example as a result of resistance to medication, your breathing muscles can fatigue and you will develop respiratory failure.
Respiratory Failure
Respiratory failure is characterized by either a reduced oxygen level or an elevated carbon dioxide level in arterial blood. In asthmatic attacks, the decrease in oxygen is usually not too severe, but may cause breathlessness, rapid breathing, and blue lips. In less severe asthmatic attacks, the respiratory rate rises and the carbon dioxide levels are usually lower than normal; this is called hyperventilation. If the carbon dioxide level is high (or even normal) during an asthma attack, it suggests that the respiratory muscles are fatigued and heralds respiratory failure. As the carbon dioxide level rises, you can become confused, sleepy and possibly comatose. The acidity of the blood is also altered, so that many vital organs cannot function normally. The reduced oxygen level in status asthmaticus is easily corrected with nasal, or face mask oxygen. The treatment of an elevated carbon dioxide level, however, usually requires mechanical ventilation.
