Expiratory air trapping during asthma exacerbation: Relationships with clinical indices and proximal airway morphology

• We visually scored expiratory air trapping (ATexp) during asthma exacerbation (AE).
• During AE, ATexp was invariably present and usually extensive.
• The total ATexp score was correlated with patient’s age, BMI, BSA and AE severity.
• The total ATexp score was correlated with bronchial wall area and thickness.
• The total ATexp score was not correlated with expiratory bronchial collapse.

ObjectivesTo semi-quantitatively assess expiratory air trapping (ATexp) and structural changes in the proximal airways in asthma during asthma exacerbation (AE) and to explore the relationships among ATexp, clinical indices, and proximal airway changes.MethodsPaired inspiratory-dynamic forced expiratory CT scans of 36 asthmatics (30 women, 6 men; mean age, 49.2 ± 18.9 years) performed during AE were retrospectively reviewed for the total ATexp score (summed scores [extent grading (0–4) × pattern grading (1–4)] of the twelve lung zones), morphologic parameters and expiratory bronchial collapse (BCexp) of the proximal airways. The relationships of the score with clinical indices and proximal airway morphology (normalized by body surface area [BSA]) were analyzed. A p value of <0.05 was considered statistically significant.ResultsThe mean total ATexp score was 110.1 ± 43.4 (range, 8–166). It was higher in the lower zones and in patients older than 60 years, having BMI of <27.5 kg/m2, and peak expiratory flow rate (PEFR) of <60% predicted. Correlation existed between the score and age (r = 0.331), BMI (r = –0.375), BSA (r = –0.442), % predicted PEFR (r = –0.332), right upper lobe apical segmental bronchus (RB1)-wall area (WA)/BSA (r = 0.467), %RB1-WA (r = 0.395), and RB1-bronchial wall thickness (BWT)/BSA (r = 0.378). The score showed no correlation with BCexp and other morphologic bronchial parameters. Area under receiver-operating-characteristic curve 0.724 (95% CI) showed that the score of 110 could discriminate patients with PEFR of <60% predicted from those with PEFR of ≥60% predicted.ConclusionDuring AE, there was a high prevalence of extensive ATexp which was correlated with patient’s age, BMI, BSA, AE severity and RB1 morphology but not correlated with BCexp.