Dynamic hyperinflation during bronchoconstriction in asthma: implications for symptom perception.

OBJECTIVE: The objective of this study was to examine the relationship between respiratory symptom intensity and quality and dynamic lung hyperinflation (DH) during induced bronchoconstriction in asthma. PATIENTS AND METHODS: Subjects with asthma (n = 116) underwent baseline spirometry and lung volume measurement followed by high-dose methacholine challenge testing (MCT) [maximum decrease in FEV(1) of 50% from baseline]. Dyspnea intensity (Borg scale) was measured after each dose of methacholine. Qualitative descriptors of breathlessness and functional residual capacity (FRC) were measured at the doses nearest to the provocative concentration of methacholine causing a 20% fall in FEV (PC(20)) and at the highest dose of methacholine (maximum response).
RESULTS: FEV(1) decreased by 24.7 +/- 0.7% (mean +/- SEM) at the dose nearest to PC(20) and by 46.1 +/- 1.1% at maximum response. Inspiratory capacity decreased by 0.62 +/- 0.04 L at the dose nearest to PC(20) and 1.06 +/- 0.06 L at maximum response. The descriptor clusters "inspiratory difficulty," "chest tightness," "unsatisfied inspiration," and "work" were selected at the dose nearest to PC(20) but were more frequently selected at maximum response (p < 0.0001). Individuals who reported chest tightness at maximum response had greater airflow obstruction and higher FRC (percentage of predicted) than those who did not report chest tightness.
CONCLUSIONS: Four dominant qualities of dyspnea in asthma (inspiratory difficulty, chest tightness, unsatisfied inspiration, and work) were reported early in the course of MCT and evolved in parallel, becoming more prevalent at maximum response. Significant DH accompanied even mild bronchoconstriction during MCT in asthma, making it difficult to separate mechanisms of chest tightness from other dominant respiratory sensations.