This is most frequently done after administration of a bronchodilator. The dose of nebulized salbutamol is 2.5 mg in 3 ml of normal saline. If a metered dose inhaler gives it, 4 puffs (360 ug) given at intervals of 30 seconds are recommended. Change in heart rate by > 10% and lasting for at least 2 minutes is confirmative of the effect of salbutamol.
Spirometry is repeated 15 minutes after short acting beta agonist and 30 minutes after an anti cholinergic inhalation. Reversibility of bronchospasm is checked. Other challenges are methacholine, histamine, leukotrienes and prostaglandins, which stimulate the smooth muscles receptors of the airway. Other ways of checking the hyper responsiveness are post exercise, dry, cold air inhalation, specific antigens, hypertonic saline and distilled water inhalation. However, these should be performed with caution.