ABSTRACT
Severe asthma is defined not only by airway obstruction unresponsive to adrenergic agents (status asthmaticus), but also by the difficulty of controlling the disease on a chronic basis. While tests of lung function such as the forced expiratory volume in 1 s (FEV1) will be uniformly abnormal in patients with status asthmaticus, asymptomatic individuals with difficult-to-control chronic asthma may at times have normal conventional tests of lung function. However, as is explored in this chapter, tests of airway function that define the level of airway responsiveness will likely be abnormal in both scenarios.
