Relationship of airway hyperresponsiveness to respiratory symptoms and diurnal peak flow variation in patients with obstructive lung disease

Hyperresponsiveness of the bronchial airways is a fundamental characteristic of a number of respiratory disorders, including asthma and chronic obstructive pulmonary disease (COPD). In general, the degree of airway hyperresponsiveness correlates with the severity of the symptoms reported by patients suffering from these diseases. However, in some cases, the degree of airway hyperresponsiveness does not seem to be predictable on the basis of symptom severity. To further characterize the relationships between airway hyperresponsiveness, respiratory symptoms, and peak expiratory flow (PEF; an index of the maximum amount of gas breathed out from the lungs), a study was carried out with 221 hyperresponsive patients with moderately severe airway obstruction. The patients were categorized as having asthma (81 patients), asthmatic bronchitis (69 patients), or chronic obstructive pulmonary disease (44 patients). Twenty-seven patients could not be accurately classified into one of these groups. Airway responsiveness was quantified by measuring the degree of bronchial constriction in response to inhaled histamine (a bronchoconstrictor substance). Average airway responsiveness was significantly higher in asthmatic patients than in either COPD or asthmatic bronchitis patients, but there was a large amount of variability in all three groups. Airway responsiveness was moderately correlated with peak expiratory flow; however, for each level of airway responsiveness, there was wide variability in the PEF values obtained, indicating that the two measures are not interchangeable. Symptom severity was weakly related to airway responsiveness and PEF levels. Hence, all three variables (airway hyperresponsiveness, peak expiratory flow, and symptom severity) appear to provide related but different information on the underlying disease process. (Consumer Summary produced by Reliance Medical Information, Inc.)