1.Introduction:
Asthma is the most common chronic lower respiratory disease in childhood, characterized by airway inflammation and airway hyper-responsiveness. Most cases of childhood asthma occur before the age of 3 years, and pulmonary impairment often starts during the preschool ages. Moreover, acute exacerbations are one of the main causes of emergency department visits and may lead to long‐term pulmonary impairment children[1-3]. Therefore, early diagnosis and early treatment are of great significance to achieve full control and reduce asthma exacerbations[4]. Lung function tests are a common detection method of asthma. Longitudinal monitoring of respiratory parameters is helpful to early intervention and improve prognosis.
Spirometry has traditionally been employed to evaluate lung function, considered as the gold standard[4]. However, young children may be unable to perform the test, since it requires effort dependent lung maneuvers. The effort dependent nature of the test interferes with the reproducibility of the test. Besides, spirometry may be limited when clinical conditions do not allow it to be carried out safely[5].
For these reasons, impulse oscillometry (IOS), based on forced oscillation technique (FOT), has been noticed to measure lung function in young children(mainly over 3 years old)[6]. Compared with spirometry, IOS is a much simpler and noninvasive technique for assessing airway impedance and responsiveness in children. It is effort-independent that can be performed in tidal breathing and requires minimal patient cooperation. Also, it can distinguish between the degree of obstruction in central and peripheral airways[7, 8]. The main indicators of IOS are R5 (resistance at 5HZ), R20 (resistance at 20HZ), R5-20 (resistance at 5 Hz minus resistance at 20 Hz), X5(reactance at 5Hz), AX(reactance area), Fres(resonant frequency of reactance).
In recent years, many studies have explored the predictive value of IOS for asthma exacerbations in childhood, but its specific indicators are still controversial. Therefore, we performed a systematic literature review and meta-analysis to further investigate the issue and identify potential sources of heterogeneity that might be confounders that have affected some existing conclusions.
2.Methods
This meta-analysis strictly followed the recommendations of the
Preferred Reporting Items for
Systematic
Reviews and Meta-analyses Statement[9]. No ethical
approval and patient consent were required for this review as all data
were already published in peer-reviewed journals.
2.1 literature search and selection criteria
We conducted a comprehensive literature search of the PubMed, Embase,
and Web of Science databases up to July 2020 with the following search
algorithm: (asthma or asthmas or bronchial asthma or asthma, bronchial)
and impulse oscillometry. Besides, the reference lists of retrieved
articles and related reviews were examined to identify any potential
relevant research. There were no language or publication date
restrictions. The flow diagram was presented in Fig. 1.
The inclusion criteria were as follows: 1.study design was randomized
controlled trials (RCT); 2. participants were children (≤14 years old)
with asthma exacerbations or poorly controlled asthma, which was
diagnosed according to the Global Initiative for Asthma or relevant
guidelines;3. participants used impulse oscillometry to evaluate lung
function;4. outcome measures included impulse oscillometry parameters.
To ensure accuracy, two authors chose the studies independently,
resolved their differences through discussion with the third author, and
selected the articles to be included by consensus.
2.2 quality assessment and data extraction
The Newcastle–Ottawa Scale (NOS) was applied to assess the quality of
included studies by two independent authors. NOS is a 9-star system,
which scores observational studies on 3 dimensions: selection (4 items),
comparability (1 item), and exposure/outcome (3 items). Except for
comparability (2 points), 1 point will be given for each item. A score
≥of 7 was considered a high-quality article.
Two authors independently abstracted data and any discrepancy was
resolved by consensus. The following variables were collected from each
study: author, publication year, country, type of study, age of
baseline, sample size and number of cases, and measurements. The outcome
of interest was parameters of IOS that can predict asthma exacerbations
or loss of control.
2.3 Statistical analyses
For studies that reported separate effect size estimates of different
related indicators of IOS in acute asthma attacks, we combined these
risk estimates into each study, weighted by the inverse of the variance.
Subgroup analyses were performed based on different parameters of IOS
related to asthma exacerbations. Heterogeneity across included studies
was assessed with the Cochrane Q test (the level of significance was set
at 0.1)[10]. The I2 score was
also used to determine the degree of heterogeneity
(I2< 50%, no obvious heterogeneity;
I2>50%, large or extreme
heterogeneity)[11]. Galbraith plot[12] introduced to identify the studies that
contributed to the heterogeneity and meta-analysis was performed again
after removing these studies.
In the sensitivity analysis, the meta-analysis was repeated after each
study was omitted. Begg’s test[13] and Egger’s
test [14] were used to assess publication bias.
Meta-analysis was conducted using STATA 12.0.