Peak expiratory flow rate (PEFR) is the best assessment of asthma severity during acute asthmatic attack (AAA). Since PEFR represents an effort-dependent flow from large airways, we wonder if the falls of PEFRs during AAA result from expiratory tracheobronchial collapses (TBC). This study aims to explore the existence of TBC during AAA and, if any, its influence on PEFR.
Methods: We conducted a cross sectional cohort in patients with AAA treated at the emergency department (ED). Along with the continued monitoring of PEFRs, TBC assessments by low dose high resolution computerized tomogram (HRCT) were performed twice for each patient, i.e. at ED (T1) and at 6th-8th week (T2) (PEFR variability <15%). TBCs in both periods were quantified and changes were compared with changes in the corresponding PEFRs.
Results: Of the 34 enrolled patients, 5 were excluded due to failures in forced expiratory maneuvers. At T1, all of the 29 patients exhibited variable degree of TBCs (% inspiration) (mean 44.05±19.79). 2nd HRCTs were not done in 5 patients for repeated exacerbations. Of the 24 patients who completed 2 HRCTs, 72.91% of them showed improvement of TBCs over time. Comparisons of the improvements of TBCs with those of PEFRs (% predicted) between T1 and T2 showed that TBC changes at the level of trachea near to the carina (L3) correlated well with PEFR changes (p<0.05, r=0.7). At T1, the magnitudes of TBCs at L3 also correlated with the corresponding PEFRs (p<0.05, r=0.5).
Conclusions: Patients with AAA demonstrated presences of TBCs of different severities which mostly improved with time. TBC at tracheal rings near to the carina was most prominent that influenced the changes of PEFRs. TBCs thus play roles in the falls of PEFRs during AAA.