Asthma and COPD are associated with inflammation of the airway mucosa. Hyperemia, exudation, transudation and hypersecretion alter both the morphology and the function of the airways.
What is this tutorial about?
Let us assume that you expose an asthmatic's and a non-asthmatic's airways to increasing concentrations of a substance that will produce airway narrowing (agonist). You measure the degree of airway narrowing as either the increase in airways resistance, or the decrease in the volume of air that can be forcibly exhaled in one second.
The degree of airway narrowing in response to the agonist is greater and occurs at a lower concentration of the agonist for the asthmatic than for the non-asthmatic subject. You therefore decide that the asthmatic airway is 'hyperreactive'. As rapid airway narrowing is mediated by smooth muscle contraction, you might conclude that 'bronchospasm' occurred, and that the difference between the asthmatic and non-asthmatic airways results from differences in the airway smooth muscle. In addition, you might conclude that the best way to prevent airway narrowing in patients with asthma is to treat them with 'bronchospasmolytics'.
Thus one assumption leads to the next one.
After you have finished this tutorial you will appreciate that the inflammatory process within the asthmatic airways is an important component of airway hyperresponsiveness, due to which they react differently than in healthy subjects. Administration of only an airway smooth muscle relaxant is therefore of limited value in controlling airways obstruction and the symptoms of asthma. It is of primary importance to prevent and treat the inflammatory process within the lung with the use of anti-inflammatory agents, such as glucocorticosteroids. Anti-inflammatory agents can reduce airways obstruction, decrease the sensitivity of the airways to agonists, and greatly decrease the requirement for bronchodilator drugs.
When you have completed the tutorial you will appreciate that the two illustrations shown here very concisely summarise the pathophysiological principles underlying bronchial hyperresponsiveness and provide a framework for prevention and therapy. 'Bronchospasm' and 'bronchospasmolysis' will no longer form part of your vocabulary.
The pathophysiological principles underlying airway responsiveness are generally applicable to biological tube systems, such as that of the (pulmonary) circulation.