Abstract
Background. Bronchial asthma is characterized by episodes of airway narrowing with dyspnoea. This is described as chest tightness, inspiratory effort, unrewarded inspiration or expiratory difficulty.
Aims. To examine if dyspnoea or its descriptors reflect different mechanical changes during bronchoconstriction.
Methods. Eighty-four mild asthmatics were challenged with methacholine. Symptoms were scored as Borg units. Lung function measurements included: 1) compression-free partial flow at 40% of vital capacity, residual volume, functional residual capacity, inspiratory resistance (R5) and reactance (X5) at 5 Hz; 2) changes in R5 and X5 with deep breath and velocity of recovery; 3) difference in resistance between 5 and 19 Hz (R5-19); 4) interquartile range (IQR) of R5, R5-19, and X5; 5) difference between inspiratory and expiratory X5 (ΔX5), as an index of expiratory flow limitation. Relationships between variables were assessed by ordinal logistic regression analysis and expressed as Odds Ratio (OR).
Results. At 25% FEV1 fall, dyspnoea was related to increased X5-IQR (OR: 8.55), inspiratory effort to ΔX5 (OR: 2.27), unrewarded inspiration to deep-breath inability to attenuate X5 fall (OR: 4.58) and expiratory difficulty to a blunted increase in R5-19-IQR (OR: 0.017). No relationships were observed between functional data and chest tightness.
Conclusions. The increments in dyspnoea, inspiratory effort and unrewarded inspiration reflect the ease with which the airways close over time, occurrence of expiratory flow limitation, and reduced recruitment of closed airways with deep breaths. The increase in expiratory difficulty appears to reflect the inability of the open peripheral airways to take different configurations with breathing.
- © 2013 ERS