|Effectiveness of cough exercise and expiratory muscle training: a meta-analysis
|Kojima H, Yamada T, Takeda M, Itou Y, Yoshida M, Kimura M
This review assessed cough exercise and expiratory muscle training for enhancing the effectiveness of coughing. The authors concluded that the forced expiration technique and coughing alone significantly increased mucus clearance. Expiratory muscle training significantly increased expiratory muscle strength. Given the methodological limitations of the trials and the review, and the limited information shown, the reliability of the conclusions is unclear.
To investigate the effects of cough exercise and expiratory muscle training (EMT) in enhancing the effectiveness of coughing.
The Cochrane Database of Systematic Reviews, the Cochrane CENTRAL Register, DARE, ACP Journal Club, CINAHL (1990 to October 2004), PEDro, MEDLINE (1966 to October 2004) and Ichushi Web (NPO Japan Medical Abstracts Society, 1983 to October 2004) were searched; the search terms were given. Reference lists might also have been searched, but this was slightly unclear. The search was restricted to trials published in English or Japanese.
The authors did not specify any inclusion criteria for the participants. Studies of coughing exercise included patients with cystic fibrosis and chronic obstructive pulmonary disease (COPD), while those studying EMT included patients with multiple sclerosis and COPD, as well as healthy participants.
Studies were eligible if they were randomised controlled trials investigating coughing exercise or EMT. The included trials investigated both coughing exercise and EMT, and appear to have used coughing alone or cough prohibition as a control intervention. The comparisons made in the included trials were cough versus no cough, forced expiration technique versus cough alone, and EMT versus control.
Studies were considered if they investigated outcomes such as weight of sputum expectorated, radioactive aerosol clearance, peak cough flow (PCF) on coughing exercise, maximal expiratory pressure (PEmax), maximal inspiratory pressure (PImax), or PCF on EMT. None of the included studies used PCF as an outcome.
Articles that fulfilled the selection criteria based on title and abstract were retrieved in full. The authors did not state how many reviewers performed the selection.
Assessment of study quality
The quality of the included studies was assessed on the basis of randomisation, similarity of the groups at baseline, intention-to-treat analysis, blinding, validity of the outcome measurement, description of exercise regimen, losses to follow-up and additional treatment received.
Two reviewers independently assessed quality, with any disagreements resolved by a third reviewer.
The authors did not state how the data were extracted for the review, or how many reviewers performed the data extraction. Effect sizes and 95% confidence intervals (CIs) were calculated.
Methods of synthesis
Effect sizes were combined in a meta-analysis using a random-effects model for each outcome. Statistical heterogeneity was assessed using the Q-statistic.
Results of the review
Ten trials (n=150) were included: 6 studies (n=74) investigated cough exercise and 4 studies (n=76) investigated EMT.
The included studies scored between 24 and 38 points (of a maximum of 40) for methodological quality. All of the coughing exercise trials were randomised crossover trials. In 9 studies the outcome assessor was not blinded or blinding of the outcome assessment was not reported. Sample sizes were small.
For studies of coughing exercise, coughing versus no coughing resulted in a significant increase in the weight of sputum expectorated (effect size 3.07, 95% CI: 0.06, 6.09) but no significant difference in radioactive aerosol clearance (effect size 4.15, 95% CI: -0.67, 8.98). Similarly, with the forced expiration technique compared with coughing alone, there was a significant increase in the weight of sputum expectorated (effect size 2.01, 95% CI: 1.06, 2.96) but not in radioactive aerosol clearance (effect size -0.34, 95% CI: -0.88, 0.21).
For studies of EMT versus control, there was a significant increase in PEmax (effect size 1.38, 95% CI: 0.74, 2.02) but not PImax (effect size 0.96, 95% CI: -0.34, 2.26).
Some heterogeneity was present in the trials. Homogeneity was found only for radioactive aerosol clearance in the evaluation of the forced expiration technique, coughing in the evaluation of coughing exercise, and PEmax in the evaluation of EMT.
Both the forced expiration technique and coughing alone significantly increased mucus clearance. EMT significantly increased expiratory muscle strength.
This review had clearly stated inclusion criteria with respect to the interventions, outcomes and study design, but not the participants. The search involved a number of relevant databases, but inclusion was restricted to studies published in English or Japanese; this might have introduced language bias. No supplementary searches (e.g. for unpublished data) were carried out, so relevant studies might have been overlooked. Since the study selection process was not described clearly and there was no description of the data extraction, it is unclear whether a systematic methodology has been applied. The validity assessment was described, but there was only a limited systematic description of the quality of the included trials. There was no detailed and systematic description of the characteristics of the trials included. Crossover trials were included, but it is unclear how these were analysed. Heterogeneity was assessed but not further explored. The results were presented without significance levels, although CIs were shown. Given the limited information provided, it is unclear to what extent the conclusions are reliable.
Implications of the review for practice and research
Practice: The authors made no specific recommendations for practice.
Research: The authors stated that further studies with larger and more diverse sample populations are necessary to determine the effects of increasing expiratory muscle strength on cough effectiveness.
Kojima H, Yamada T, Takeda M, Itou Y, Yoshida M, Kimura M. Effectiveness of cough exercise and expiratory muscle training: a meta-analysis. Journal of Physical Therapy Science 2006; 18(1): 5-10
Subject indexing assigned by CRD
Exercise Test /methods; Exercise Therapy /methods; Exhalation; Inhalation; Lung /physiopathology; Respiratory Function Tests /methods; Respiratory Muscles /physiopathology; Treatment Outcome
Date bibliographic record published
Date abstract record published
This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.