Reversibility test in the early stages of bronchial asthma

Small Airways Response to Bronchodilators in Adults with Asthma or COPD: A Systematic Review

BACKGROUND

Bronchodilator responsiveness (BDR) is commonly used in the diagnosis of lung disease. Although small airways dysfunction is a feature of asthma and COPD, physiological tests of small airways are not included in guidelines for BDR testing. This systematic review assessed the current evidence of BDR using small airways function in asthma and COPD.

METHODS

The systematic review used standard methodology with the protocol prospectively registered on PROSPERO (CRD42020164140). Electronic medical databases (EMBASE and Medline) were searched using related keywords. Abstracts and full texts were screened independently by two reviewers. Studies that reported the change of physiological small airways function and FEV₁ were included in the review. The revised Cochrane risk of bias tool for RCT and NIH quality assessment tool for cohort and cross-sectional studies were used to evaluate the studies.

RESULTS

A total of 934 articles were identified, with 12 meeting the inclusion criteria. Ten studies included asthma patients, 1 study included COPD patients and 1 study included both asthma and COPD. A total of 1104 participants were included, of whom 941 were asthmatic, 64 had COPD and 109 were healthy controls. Studies were heterogeneous in design including the device, dose and time intervals for BDR assessment. A small airway BDR was seen for most tests in asthma and COPD, including oscillometry (R5-20, reactance (X5), area of reactance (AX) and resonant frequency (Fres)) and Maximal Mid Expiratory Flow.

CONCLUSION

There is a measurable BDR in the small airways. However, with no consensus on how to assess BDR, studies were heterogeneous. Further research is needed to inform how BDR should be assessed, its clinical impact and place in routine clinical practice.

Small airway impairment and bronchial hyperresponsiveness in asthma onset

Purpose

Our study tried to find a relationship between baseline FEF_25-75% and airway hyperresponsiveness (AHR) and whether a greater FEF_25-75% impairment may be a marker of a more severe hyperresponsiveness in subjects with normal FEV1 and FEV1/FVC and suggestive asthma symptoms. Besides, we tried to asses a FEF_25-75% cut-off value to identify hyper-reactive subjects.

Methods

4,172 subjects (2,042 M; mean age: 38.3±14.9; mean FEV1 % predicted: 100.5±12.7 and FEV1/FVC: 85.4±6.8) were examined after performing a methacholine (Mch) test. All subjects reported a symptom onset within 3 years before the test. Subjects with PD20<400 or >400 µg were arbitrarily considered affected by moderate/severe and borderline AHR, respectively.

Results

PD20 values were 213 (IQR:86-557), 340 (IQR:157-872) and 433 (IQR:196-1032) µg in subjects with baseline FEF_25-75≤50%, FEF_25-75 between 50 and 70% and FEF_25-75>70% respectively (P<0.0001). Only in moderate/severe hyper-reactive subjects (excluded borderlines), PD20 was lower in the FEF_25-75≤50% subgroup than in the 1 with FEF_25-75>70%. The hyperreactive subjects percentage, was higher in those with FEF_25-75≤50% and lower in those with FEF_25-75>70% (P<0.0001). FEF_25-75<50% (compared to FEF_25-75>70%) was a higher AHR risk factor, especially in subjects with moderate/severe AHR (OR: 2.18 [IQR:1.41-3.37]; P<0.0001). Thresholds yielding the highest combined sensitivity/specificity for FEF_25-75% were 75.19 (area under curve [AUC]: 0.653) and 74.95 (AUC:0.688) in subjects with PD20<2,400 and <400 µg respectively. FEV1, FVC, and FEV1/FVC measured in subjects with different FEF_25-75≤50%, FEF_25-75>50 and ≤70% or FEF_25-75>70% levels were similar both in normoreactive and hyperreactive subjects.

Conclusions

At asthma onset, reduced baseline FEF_25-75 values with normal FEV1 and FEV1/FVC may predict AHR. Detectable predictive cut-off values do not exist because even normoreactive subjects can show lower FEF_25-75 values. Furthermore, a greater FEF_25-75 reduction may be associated to a more severe AHR, suggesting a possible FEF_25-75 role in the management of asthma when FEV1 and FEV1/FVC are normal.