ASTHMA

ASTHMA - a patient's guide
Dr Adrian Harrison - Chest Specialist, Mercy Hospital

What is asthma?

Asthma is an inflammatory condition of the breathing tubes (or bronchi). The inflammation causes airway irritability and results in airway narrowing (called bronchospasm).

Now, to explain that in a little more detail, let's go back a few steps.

How the lungs work

Our breathing "equipment" is made up of two parts: a set of breathing tubes - similar to the trunk and branches of a tree, except that our breathing tubes, of course, are hollow. At the end of the finest branches of a tree there are leaves. In our bodies, instead of leaves, our lungs are made up of a sponge tissue.

Inhaled air travels down the breathing tubes, out to the finest branches, which are in close communication with blood vessels containing blood. The blood takes the oxygen from the air and carbon dioxide travels in the other direction, from the blood stream back into the airways, where it is breathed out.

The process of gas exchange occurs in the sponge tissue of the lung. The job of the breathing tubes is to get the air in and the carbon dioxide out.

What is different about the lungs in asthma?

In asthma, the sponge tissue works well. The problem lies in the breathing tubes.

The breathing tubes (bronchi) have an inner lining, which is similar to the lining of your mouth. In the middle of the airway wall is a layer of muscle. In asthma, this muscle layer is very irritable or "twitchy" so that a wide variety of trigger factors cause it to tighten. This causes narrowing of the breathing tubes, making it harder to breathe, and also causing chest tightness, wheezing and coughing.

Why is the muscle layer in the breathing tubes so irritable? By far the main reason for this is inflammation. An example of inflammation elsewhere in the body is sunburn. Inflamed tissues are red and swollen. In asthma the lining of the breathing tubes are inflamed.

a) Inflamed tissue contains a large number of white blood cells and these are like tiny chemical factories. The substances they release have a number of harmful effects. They cause blood vessels to become leaky so that fluid seeps out into the tissues - the tissues then become swollen.

b) Other chemicals or substances from the white blood cells attack the inner lining layer of the breathing tubes, causing it to become so damaged that, under the microscope, it looks as though the lining layer has been attacked with sandpaper. Because of this damage, infections and irritating substances we breathe in can affect the breathing tubes more easily and cause problems.
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