Asthma

What is asthma?

The variability of asthma

Most people would recognise asthma in a child or adult as attacks of wheezy breathlessness, sometimes on exertion, sometimes at rest, sometimes mild,

sometimes severe. Some would recognise specific ‘triggers’ – for example, animals, fumes, pollens. Some might think of asthma as a condition of children, some as a condition able to affect someone of any age. Some would regard it as an occasional nuisance requiring intermittent treatment only, others as a persistent, significant problem needing continuous treatment. Surely they can’t all be right? In a way they can, although it is this wide range of factors involved in asthma that makes it difficult to come up with a simple definition.

How can asthma be defined?

The word ‘asthma’ is used as a blanket term to cover a condition characterised by episodes of breathlessness caused by intermittent narrowing of the bronchial tubes – or airways – within the lung.

There are many factors that contribute to the development of asthma in the first instance and many that can induce attacks. In addition, these will vary from individual to individual.

The best definition is that asthma is a condition in which the airways within the lung are inflamed and so are more sensitive to specific factors (triggers) that cause the airways to narrow, reducing airflow through them and making the individual breathless and/or wheezy. This sensitivity of the airways enjoys the medical label ‘bronchial hyper-reactivity’. In the surgery or clinic doctors use the term ‘twitchy tubes’!

Normal breathing and asthma

So, why should this sensitivity result in the symptoms so well recognised by each individual with asthma? During most of our waking hours (and all those spent asleep) we are unaware of the gentle movement of the chest which allows oxygen-rich air to be inhaled and waste air, laden with carbon dioxide, to be expelled. We do this automatically because the natural tendency of the lungs and the chest wall is to collapse inwards, so automatic nerve pathways monitor the levels of oxygen and carbon dioxide in the blood and make the chest and therefore the lungs expand to open them up. This easy, untroubled breathing all depends upon air getting in and out of the lung through the branching system of bronchial tubes without any resistance.

Problems arise when the bronchial tubes narrow down, making the flow of air more difficult. In asthma, the narrowing occurs mostly in the smaller bronchial tubes, of which the smallest are about the diameter of a human hair, which open out into the alveoli (or air sacs). Each of these is about the size of the full stop at the end of this sentence, and this is where the inhaled oxygen diffuses easily into the blood vessels covering their surface and the carbon dioxide equally easily diffuses out.

If you spread all the alveoli in a pair of human lungs out, they would cover the area of a tennis court, which shows how well the lungs are suited to exchanging gases easily.

When the bronchial tubes narrow in asthma (the reasons for which I will explain), the flow of air through them drops quite quickly, so to overcome this resistance the chest wall muscles have to work harder to get the air in and out at the rate required to keep oxygen supplies constant. This becomes noticeable to that individual – he or she has to work harder to breathe and becomes breathless. As any musician knows, if you blow air through narrow tubes, noise will be generated – wheezing.

So asthma is not one disease: it covers a multitude of different patterns. Like the word ‘cancer’ it tells you roughly what sort of condition we are dealing with, what ballpark we are in. Under that general heading you will find a range of severities, a range of triggering factors and a range of outcomes. It logically follows that what is good for one person with asthma may be unsuitable for another.

Asthma is a very individual condition and management needs to be personalised because of the variety of factors that underlie each individual’s asthma.

KEY POINTS

• Asthma is not one disease. Like the word ‘cancer’ it covers a multitude of different patterns

• As a result of the wide range of factors involved in causing asthma and the variety of responses that the body’s airways make, it is not easy to define asthma simply