Short Definition
Asthma is defined in Essential Allergy, by Niels Mygind, Ronald Dahl, Soren Pedersen and Kristian Thestrup-Pedersen 2nd edition as : a lung disease characterized by: 1, variable and reversible airway obstruction; 2, airway inflammation; and 3, bronchial hyper-responsiveness.
A medical description of asthma
Asthma is a disease causing difficulty in breathing, with recognisable symptoms: episodic wheezy breathlessness, which varies considerably within short periods of time, and is reversible (but not completely so in some patients) either spontaneously or with treatment; most important is a significant response to beta2 agonists and to corticosteroid drugs (Table 1).

Characteristics of Asthma

1. Episodes of wheezy difficulty in breathing
2. Narrowing of the air passages in the lungs and hence increased resistance to airflow.
   The narrowing is due to different combinations of:
   1. contraction of muscles around the air passages
   2. swelling of the airway lining due to airway inflammation
   3. excessive mucus in the airways
3. Rapid and considerable changes in airway obstruction (peak flow variation >= 20%)
4. Frequent nocturnal episodes and low morning peak flow values
5. Significant reversibility with drugs which resemble adrenaline, the beta2 agonists
6. Significant reversibility with steroid drugs
7. Symptom-free periods
8. Frequent occurrence of allergy
9. Inflammation of the air passages, characterised by eosinophils in the airway wall
10. Bronchial hyper-responsiveness to nonspecific stimuli such as cold air or histamine

Table 1. Characteristics of asthma in 10 points


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Three facts stand out about asthma.

Drugs, such as those resembling two of our hormones, help asthma.

These two hormones are adrenaline (epinephrine in the USA) and hydrocortisone (a steroid). In practice we use modified forms of these hormones to get fewer side effects.
Adrenaline (epinephrine) shoots into our bloodstream when we have a sudden fright or emergency. It is the quick-acting hormone from the middle of the adrenal glands near our kidneys. It makes your pulse race, makes your heart thump, and readies your body for emergency action. In asthma, the medicines which resemble adrenaline quickly relieve asthma for a short time. So they are called 'relievers'.

Hydrocortisone comes from the outer part of our adrenal glands, called the 'cortex'. It is also partly an emergency hormone but it works much more slowly, for much longer, and in a completely different way from adrenaline. Medicines which resemble it act slowly make the lining of air tubes in asthma more normal. So your asthma becomes less bad and you are less likely to get asthma attacks. So these steroid medicines are called 'preventers'. There are other asthma 'preventers', but the steroids are the most powerful.

Most people who have asthma should have both of these kind