Question 2b

Which three factors determine the difference in bronchial responsiveness between healthy subjects and patients with asthma?

Answer

• Plateau response, sensitivity and reactivity

You are absolutely right. Just in case you guessed the right answer, let us summarize how in general asthmatics differ from healthy subjects:

• Airway sensitivity is increased: airway narrowing occurs at low concentrations of the agonist;
• The reactivity is increased: once the airway responds, the degree of airway narrowing per unit of agonist is greater, i.e. the slope of the dose-response curve is steeper;
• The maximal response is increased in the asthmatic. In non-asthmatic subjects, asthmatic subjects with mild increase in airway responsiveness, and some patients with COPD a plateau in airway narrowing is achieved at high dosages of agonist. Increasing the dose does not produce further airway narrowing. The asthmatic with mild disease and the patient with COPD have response plateaus but there is greater airway narrowing than in the non-asthmatic. In patients with moderate or severe asthma, a plateau is not obtained. The bronchial challenge has to be stopped at relatively low doses of agonist due to symptoms of severe airways obstruction.