General Paediatrics, Asthma and Allergy

Dr John Chapman   FRCPCH
  Consultant Paediatrician (NHS & Private)

Making sick children better.

What is asthma?

This is a simple question with a complicated answer. I will try to cover the main points but still keep my explanation simple. 

Let's go on a journey into your lungs starting at your mouth. Behind the tongue, is the voice box. 

Beyond the voice box, is the trachea, which is a simple stiff tube. The trachea then splits into two smaller tubes (bronchi) and these tubes split into two and so on. The tubes get smaller and smaller as we get deeper and deeper into the substance if the lungs. Bronchi split to form bronchioles and these split until they end in an air sac called the alveolus which is like a little bubble. It is here that oxygen passes into the body and carbon dioxide comes out. 
Asthma is a disease of the large bronchioles. These bronchioles are lined with airway skin (epithelium) and surrounded on the outside by muscles. 

If you have asthma, your airway epithelium is swollen and sticky - a bit like you might see in active eczema - it is a similar disease after all. 

If you have asthma, your airway muscle is very twitchy and when it contract is squeezes the bronchioles. This, combined with the swollen epithelium causes narrowing of the tube which makes it difficult to breathe through. 
The muscle twitchiness and airway swelling are made worse by viral infections (colds and flu) and by contact with allergens such as cat spit, grass pollen or house dust mite. 
And, like any muscle, the more you use your airway muscle the bigger and stronger it gets. Which means that untreated asthma can get worse and worse. 

Salbutamol, in the blue inhaler, relaxes the airway muscle very quickly and very effectively. This effect lasts for several hours and then the muscle returns to its previous twitchy state. Salbutamol does nothing for the airway swelling. 

Inhaled steroids (and steroid tablets such as prednisolone) act on the airway swelling AND the muscle twitch but only slowly. They can take a couple of months to start working but they will eventually remove the swelling AND stop the twitch long term. If you take these for a couple of years then your lungs will be identical to those of a non-asthmatic. Even the pumped up muscle will go back to a normal size. 

This why you should take your inhaled steroids every single day even when you are well. 

There are many other very good asthma medicines.

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