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Breathing exercises for adults with asthma

  1. Diana A Freitas1,
  2. Elizabeth A Holloway2,
  3. Selma S Bruno1,
  4. Gabriela SS Chaves1,
  5. Guilherme AF Fregonezi3,
  6. Karla MPP Mendonça3,*

Editorial Group: Cochrane Airways Group

Published Online: 1 OCT 2013

Assessed as up-to-date: 30 JAN 2013

DOI: 10.1002/14651858.CD001277.pub3


How to Cite

Freitas DA, Holloway EA, Bruno SS, Chaves GSS, Fregonezi GAF, Mendonça KMPP. Breathing exercises for adults with asthma. Cochrane Database of Systematic Reviews 2013, Issue 10. Art. No.: CD001277. DOI: 10.1002/14651858.CD001277.pub3.

Author Information

  1. 1

    Federal University of Rio Grande do Norte, Department of Physical Therapy, Natal, Rio Grande do Norte, Brazil

  2. 2

    University College London, Department of Epidemiology and Public Health, London, UK

  3. 3

    Federal University of Rio Grande do Norte, PhD Program in Physical Therapy, Natal, Rio Grande do Norte, Brazil

*Karla MPP Mendonça, PhD Program in Physical Therapy, Federal University of Rio Grande do Norte, Avenida Senador Salgado Filho, 3000, Bairro Lagoa Nova, Natal, Rio Grande do Norte, 59078-970, Brazil. kmorganna@ufrnet.br.

Publication History

  1. Publication Status: New search for studies and content updated (conclusions changed)
  2. Published Online: 1 OCT 2013

SEARCH

 

Summary of findings    [Explanations]

  1. Top of page
  2. Summary of findings    [Explanations]
  3. Background
  4. Objectives
  5. Methods
  6. Results
  7. Discussion
  8. Authors' conclusions
  9. Acknowledgements
  10. Data and analyses
  11. Appendices
  12. What's new
  13. History
  14. Contributions of authors
  15. Declarations of interest
  16. Index terms

 
Summary of findings for the main comparison.

Breathing exercises compared with inactive control for asthma

Patient or population: adults with asthma

Settings: outpatient

Intervention: breathing exercises

Comparison: inactive control

OutcomesIllustrative comparative risks* (95% CI)Relative effect
(95% CI)
No of participants
(studies)
Quality of the evidence
(GRADE)
Comments

Assumed riskCorresponding risk

Inactive controlBreathing exercises

Change in AQLQ

Follow-up: 8 weeks to 3 months
Mean AQLQ score ranged across control groups from 0.14 to 4.5Mean AQLQ score in the intervention groups was 0.79 higher
(0.50 to 1.08 higher)
MD 0.79 (0.50 to 1.08)172 (2 studies)⊕⊝⊝⊝
very lowa
I2 = 43%

Change in SGRQ

Follow-up: 6 and 12 months
See commentSee commentNot

estimable
78 at 6 months post baseline (1 study)

72 at 12 months post baseline (1 study)
⊕⊝⊝⊝

very lowb,c
Only one trial contributed to this outcome, so we were unable to pool data

Asthma symptoms

Measured by the Nijmegen questionnaire

Follow-up: 6 months to 12 months
Mean asthma symptoms ranged across control groups from 15 to 16.4Mean asthma symptoms in the intervention groups was 3.22 lower
(6.31 to 0.13 lower)
MD -3.22 (-6.31 to -0.13)118 (2 studies)⊕⊝⊝⊝
very lowb
I2 = 0%

Number of acute exacerbations

Number of attacks recorded by a diary

Follow-up: 6 to 54 months
See commentSee commentNot

estimable
106 (1 study)⊕⊝⊝⊝
very lowd
Only one trial contributed to this outcome, so we were unable to pool data

Inpatient hospitalisation episodesSee commentSee commentSee commentSee commentSee commentNo studies reported this outcome

Lung function (FEV1)

Percentage of predicted

Follow-up: 8 weeks
Mean FEV1 ranged across control groups from 59.9% to 77.26%See commentNot

estimable
177 (2 studies)⊕⊝⊝⊝
very lowd,e
We were unable to pool data for this outcome because of substantial heterogeneity

Days off workSee commentSee commentSee commentSee commentSee commentNo studies reported this outcome

*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
AQLQ: Asthma Quality of Life Questionnaire; CI: Confidence interval; FEV1: forced expiratory volume in 1 second; SGRQ: St George’s Respiratory Questionnaire.

 a(-1 limitations) Methods of randomisation and allocation concealment and any attempts to blind outcome assessors were not described in one study assessing this outcome.
b(-1 limitations) One study with a high risk of bias for 'blinding of outcome assessment' due to lack of blinding.
cSingle study.
d(-1 limitations) Methods of randomisation and allocation concealment and any attempts to blind outcome assessors were not described in the studies assessing this outcome.
eSubstantial heterogeneity (I2 = 82%).

 

Background

  1. Top of page
  2. Summary of findings    [Explanations]
  3. Background
  4. Objectives
  5. Methods
  6. Results
  7. Discussion
  8. Authors' conclusions
  9. Acknowledgements
  10. Data and analyses
  11. Appendices
  12. What's new
  13. History
  14. Contributions of authors
  15. Declarations of interest
  16. Index terms
 

Description of the condition

Asthma is a chronic inflammatory disorder of the lungs that can lead to structural and functional changes, resulting in bronchial hyperresponsiveness and airflow obstruction (Taylor 2008; Holgate 2009; Zhang 2010; Allen 2012; Brightling 2012). Symptoms of asthma include recurrent episodes of wheeze, cough, breathlessness and chest tightness, together with episodes of marked worsening of symptoms, known as exacerbations (Bateman 2008; Zhang 2010; Brightling 2012).

The diagnosis of asthma is based on the individual's medical history, physical examination findings and lung function and laboratory test results (Sveum 2012). Measurement of lung function provides an assessment of the severity of airflow limitation. These measures yield complementary information about different aspects of asthma control and are obtained by spirometry and by peak expiratory flow measurement (GINA 2011). Assessment of airway responsiveness to factors that can cause asthma symptoms, evaluation of airway inflammation and measurement of allergic status may facilitate the diagnosis of patients with asthma (GINA 2011).

Asthma is a serious public health problem that is a major cause of disability and health resource utilisation for those affected (Bateman 2008; Eisner 2012; To 2012). Around 300 million individuals of all ages worldwide are affected by asthma (Bateman 2008; Bousquet 2010; Brightling 2012). Increases in morbidity, mortality and economic costs are associated with severe or difficult to treat asthma, particularly in industrialised countries (Zhang 2010; Eisner 2012).

Asthma has been associated with symptomatic hyperventilation, which decreases carbon dioxide (CO2) levels, causing hypocapnia (Thomas 2001; Laffey 2002; Bruton 2005a). Hypocapnia resulting from hyperventilation may perpetuate the bronchospasm and culminate in a cycle of progressive hypocapnia and increasing bronchospasm (Laffey 2002). Thus, hypocapnia may contribute to increased airway resistance in patients with asthma (van den Elshout 1991; Laffey 2002). This fact has led to increasing interest in strategies that can be used to reduce hyperventilation. In addition, psychological symptoms may interfere with the severity of the respiratory symptoms and may influence patients’ quality of life (Rimington 2001; Juniper 2004). Thus, an important component of asthma management is identifying individual issues that impair health-related quality of life and treating them (Rimington 2001; Juniper 2004).

 

Description of the intervention

Although no cure for asthma is known, its symptoms are controllable in most patients (Taylor 2008). Asthma treatment can be pharmacological or non-pharmacological or a combination of the two associated with strategies of symptom control (environmental triggers and asthma education) (Wolf 2008; Burgess 2011; GINA 2011; Welsh 2011).

Medications to treat asthma can be broadly divided into long-term controllers and short-term relievers (Arun 2012). Controller medications are taken daily on a long-term basis, and the relievers are used to rapidly decrease bronchoconstriction and relieve its symptoms (GINA 2011). Such treatment can be administered in different ways (by inhalation, orally or parenterally) (GINA 2011).  

Non-pharmacological interventions have gained attention in the treatment of asthma. Complementary and alternative medicine includes breathing exercises, homeopathy, acupuncture, aromatherapy, reflexology, massage, inspiratory muscle training and the Alexander technique (Blanc 2001; Ram 2009; Dennis 2012; McCarney 2012). Breathing exercises have been used routinely by physiotherapists and other professionals to control the hyperventilation symptoms of asthma (Bruton 2005b) and can be performed as the Papworth method, Buteyko breathing technique, yoga or any other similar intervention that manipulates the breathing pattern (Ram 2003). 

 

How the intervention might work

Work undertaken at the Papworth Hospital, in Cambridge, UK, has changed the techniques used for treatment of asthma and hyperventilation (Cluff 1984; Innocenti 1993; Holloway 1994; Lum 1994). The Papworth method focuses on the use of an appropriate breathing pattern to reduce hyperventilation and hyperinflation, therefore increasing CO2 levels and thus reducing the effects of hypocapnia and some symptoms attributed to asthma crisis.

The Buteyko method was developed in the 1950s by Konstantin Buteyko; the rationale behind its use is similar to that of the Papworth method for people who experience hypocapnia as a major contributor to their asthma symptoms. This method aims to develop a more efficient pattern of respiration through the use of controlled breathing and respiratory pauses. As a result, the method intends to increase alveolar and arterial CO2 tension, which may reverse bronchospasm, normalise the breathing pattern and reduce breathlessness (Bruton 2005b; Burgess 2011).

Yoga is an ancient discipline from India that has been shown to be an alternative technique for the management of asthma to help reduce anxiety associated with asthma symptoms. Some mechanisms may explain the rationale for yoga, such as reduction in psychological overactivity and emotional instability, and thereby reduction in efferent vagal discharge; increased autonomic control; decreased vagal outflow to the lung causing bronchodilatation and decreased bronchial reactivity (Singh 1990a). Yoga breathing techniques include deep breathing exercises (pranayama), which deal explicitly with control of breathing, postures (asanas), cleansing techniques (kriyas), meditation, prayer and often dietary changes to reduce asthma symptoms (Burgess 2011).

 

Why it is important to do this review

The worldwide high prevalence of asthma has become a public health problem because of the high healthcare costs resulting from hospitalisation and medication (Giavina-Bianchi 2010).

Breathing exercises have been used widely as an adjunct therapy in the treatment of asthmatic patients, generating considerable interest among researchers to develop studies that seek to show evidence of the effectiveness of this intervention.

This is an update of a review last published in 2003, in which the review authors concluded that there was insufficient evidence on the clinical benefits of breathing exercises in patients with asthma. Recently, new studies have been conducted to evaluate the effects of breathing exercises on quality of life, symptom control and lung function in asthmatic patients. Thus, within this review update, we aim to summarise and assess evidence from randomised controlled trials showing the efficacy of breathing exercises in the treatment of patients with asthma.  

 

Objectives

  1. Top of page
  2. Summary of findings    [Explanations]
  3. Background
  4. Objectives
  5. Methods
  6. Results
  7. Discussion
  8. Authors' conclusions
  9. Acknowledgements
  10. Data and analyses
  11. Appendices
  12. What's new
  13. History
  14. Contributions of authors
  15. Declarations of interest
  16. Index terms

To evaluate the evidence for the efficacy of breathing exercises in the management of patients with asthma.

 

Methods

  1. Top of page
  2. Summary of findings    [Explanations]
  3. Background
  4. Objectives
  5. Methods
  6. Results
  7. Discussion
  8. Authors' conclusions
  9. Acknowledgements
  10. Data and analyses
  11. Appendices
  12. What's new
  13. History
  14. Contributions of authors
  15. Declarations of interest
  16. Index terms
 

Criteria for considering studies for this review

 

Types of studies

Randomised controlled trials of breathing exercises in adults with asthma.

 

Types of participants

Adult patients with physician diagnosed asthma and/or diagnosis by internationally established criteria: American Thoracic Society (ATS), European Respiratory Society (ERS) or British Thoracic Society (BTS). Patients may be either community or hospital based with their treatment supervised by a general practitioner or respiratory specialist.

 

Types of interventions

Intervention: Patients with asthma who have received at least one course of treatment comprising breathing retraining.

Comparison: Control group receiving asthma education or, alternatively, no active control group (e.g. waiting list control).

 

Types of outcome measures

 

Primary outcomes

  • Quality of life.

 

Secondary outcomes

  • Asthma symptoms (e.g. measures of dyspnoea or breathlessness with Borg score or visual analogue scale).
  • Number of acute exacerbations (mean number and number of participants experiencing one or more exacerbations).
  • Inpatient hospitalisation episodes.
  • Physiological measures—lung function (especially low flow rates) and functional capacity.
  • General practitioner (GP) or hospital outpatient appointments or both.
  • Days off work.
  • Patient's subjective evaluation of the intervention.

 

Search methods for identification of studies

 

Electronic searches

Trials were identified from the Cochrane Airways Group Specialised Register of Trials (CAGR), which is derived from systematic searches of bibliographic databases including the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, CINAHL, AMED and PsycINFO, and from handsearching of respiratory journals and meeting abstracts (see Appendix 1 for further details). All records in the CAGR coded as 'asthma' were searched using the following terms:

((breath*) and (technique* or exercise* or re-train* or train* or re-educat* or educat* or physiotherap* or "physical therap*" or "respiratory therapy")) or (buteyko or "qigong yangsheng" or pranayama* OR yoga*) or "breathing control"

For the previous version of this review, searches were conducted up to April 2003. For this version, the literature search has been updated to February 2012. A repeat search was undertaken in January 2013.

 

Searching other resources

Reference lists of relevant articles found by the above methods were consulted to look for additional studies, and a search in clinical trial registries (clinicaltrials.gov and the WHO trial portal) was undertaken to look for planned, ongoing and unpublished trials.

 

Data collection and analysis

 

Selection of studies

Two review authors (DAF and GSSC) independently assessed studies for the possibility of inclusion in this review. We retrieved full text articles and reviewed them to determine eligibility. Final decisions and disagreements were resolved by consultation with a third review author (KMPPM).

 

Data extraction and management

Two review authors (DAF and GSSC) independently extracted data into RevMan (RevMan 2011) by using a standard data collection form. According to methods described in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011a), we collected information from the studies, including the following.

  • Methods (design, method of randomisation, method of allocation concealment, outcome assessor blinding, withdrawal and dropouts).
  • Participants (country, health status, mean age, gender, total sample and exclusion criteria).
  • Interventions (methods and types of intervention, including number and duration of sessions and methods used for control group comparisons).
  • Outcomes (improvement in quality of life indices, asthma symptoms, number of acute exacerbations, inpatient hospitalisation episodes, etc).

We resolved disagreements by discussion and consensus.

 

Assessment of risk of bias in included studies

Two review authors (DAF and GSSC) independently assessed the risk of bias using The Cochrane Collaboration’s tool for assessing risk of bias, which includes the following items: random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective reporting and other sources of bias. The risk of bias was classified as high, low or unclear, according to the methods described in Chapter 8 of the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011b). Disagreements were resolved by discussion and consensus.

 

Measures of treatment effect

Continuous outcomes were expressed as mean difference (MD) with 95% confidence interval (CI) when outcome measurements were performed on the same scale, or as standardised mean difference (SMD) with 95% CI when studies assessed an outcome by using different methods.

 

Unit of analysis issues

Trials with a cross-over and cluster-randomised design were not included in the review.

 

Dealing with missing data

We wrote to authors of included trials to request additional data as required.

 

Assessment of heterogeneity

We assessed heterogeneity by inspecting the forest plots to detect non-overlapping CIs, while applying the Chi2 test with a P value of 0.10 indicating statistical significance. We also implemented the I2 statistic, with a value of 50% denoting moderate levels of heterogeneity and above 50% indicating a substantial level of heterogeneity (Higgins 2011c).

 

Assessment of reporting biases

If we had been able to meta-analyse sufficient data (10 studies or more), we planned to assess reporting bias among the studies using the funnel plot method discussed in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011d). If asymmetry was noted, we planned to explore possible causes, including publication bias, poor methodological quality and true heterogeneity.

 

Data synthesis

We used The Cochrane Collaboration's statistical package, Review Manager, to combine outcomes when possible (RevMan 2011). We used a fixed-effect model unless substantial heterogeneity (a value of I2 greater than 50%) was obtained, in which case we used a random-effects model. For trials with more than two arms, we split the control group to avoid double counting.

We created a 'Summary of findings' table that included the following outcomes, according to the methods described in Chapter 11 of the Cochrane Handbook for Systematic Reviews of Interventions: change in Asthma Quality of Life Questionnaire (AQLQ), change in St George's Respiratory Questionnaire (SGRQ), asthma symptoms, number of acute exacerbations, inpatient hospitalisation episodes, lung function (forced expiratory volume in 1 second (FEV1)) and days off work.

 

Subgroup analysis and investigation of heterogeneity

If we were able to combine sufficient data and identify substantial heterogeneity (a value of I2 greater than 50%), we planned to conduct the following subgroup analyses.

  • Degree of asthma severity.
  • Age groups (adult versus elderly).
  • Duration of treatment.

 

Sensitivity analysis

If we had been able to combine sufficient data, sensitivity analysis would have been performed to explore the influence on the results of the following factors.

  • Trial quality (randomised controlled trials with poor methodology).
  • Trial size (stratified by sample size).
  • Allocation concealment (high risk of bias versus low risk of bias versus unclear risk of bias).
  • Assessor blinding (high risk of bias versus low risk of bias versus unclear risk of bias).

 

 

Results

  1. Top of page
  2. Summary of findings    [Explanations]
  3. Background
  4. Objectives
  5. Methods
  6. Results
  7. Discussion
  8. Authors' conclusions
  9. Acknowledgements
  10. Data and analyses
  11. Appendices
  12. What's new
  13. History
  14. Contributions of authors
  15. Declarations of interest
  16. Index terms
 

Description of studies

 

Results of the search

For the initial version of the review (1998), full texts of 42 potentially relevant studies were obtained after 182 abstracts and titles revealed by the searches were screened; five studies were included (Nagarathna 1985; Girodo 1992; Fluge 1994; Bowler 1998; Vedanthan 1998). In the 2003 update, two more studies were included (Opat 2000; Thomas 2003). The search of the Airways Group Register for the 2012 update returned 147 references. Of these, twelve were identified as potentially relevant, and the full text articles were retrieved for closer inspection, of which five were new additions in the 2012 update (Holloway 2007; Thomas 2009; Sodhi 2009; Vempati 2009; Grammatopoulou 2011). A repeat search was undertaken from February 2012 to January 2013, and 12 new references were identified. Of these, three were considered eligible and thus were included in the review (Bidwell 2012; Singh 2012Prem 2013).  

We excluded two studies that were included in earlier versions of this review (see Excluded studies).

 

Included studies

In total, 13 studies are now included in this review: Nagarathna 1985; Girodo 1992; Fluge 1994; Vedanthan 1998; Thomas 2003; Holloway 2007; Thomas 2009; Sodhi 2009; Vempati 2009; Grammatopoulou 2011; Bidwell 2012; Singh 2012Prem 2013. See 'Characteristics of included studies' for full details on each study.

 
Setting and populations

Five trials were conducted in India (Nagarathna 1985; Sodhi 2009; Vempati 2009; Singh 2012Prem 2013), one in Canada (Girodo 1992), one in Germany (Fluge 1994), three in the UK (Thomas 2003; Holloway 2007; Thomas 2009), two in the USA (Vedanthan 1998; Bidwell 2012) and one in Greece (Grammatopoulou 2011). All papers were written in English with the exception of Fluge 1994, which was written in German. Nine studies were conducted between 2003 and 2013, three were conducted between 1992 and 1998 and one was conducted in 1985. The studies varied in size from 17 to 183 participants. Participants in the included studies were older than 18 years of age, with the exception of Nagarathna 1985 (aged 9 to 47), Thomas 2003 (aged 17 to 65) and Holloway 2007 (aged 16 to 70). We included all studies as the mean age was over 18.

 
Interventions and control groups

In seven studies (Nagarathna 1985; Fluge 1994; Vedanthan 1998; Sodhi 2009; Vempati 2009; Bidwell 2012; Singh 2012), participants undertook yoga training that involved breathing exercises as the major component, and the control groups did not undergo yoga training but continued taking their usual medication. In Nagarathna 1985, participants in the intervention group underwent training for two weeks and were told to practise these exercises for 65 minutes daily. In Fluge 1994, participants underwent 15 yoga sessions over 3 weeks. In Vedanthan 1998, yoga sessions were performed 3 times a week over 16 weeks. In Sodhi 2009, each yoga training session was of 45 minutes' duration per week with a trained instructor for a period of 8 weeks. In Vempati 2009, the intervention consisted of 2-week supervised training in lifestyle modification and stress management based on yoga followed by closely monitored continuation of these practises at home for 6 weeks. In Bidwell 2012, yoga training consisted of two 1-hour supervised yoga sessions per week for 10 weeks. In Singh 2012, participants attended yoga training provided by a yoga expert for 5 to 6 days. Thereafter, participants were told to practise yoga for an average of 40 to 50 minutes daily at home for 2 months. Participants were called to the yoga centre regularly (about every 7 days) so investigators could see whether they were doing the yoga exercises properly.

In the Girodo 1992 study, participants undertook a 16-week programme of deep diaphragmatic breathing exercises and were compared against a group of controls that were on a waiting list. Thomas 2003 compared participants who completed three short breathing retraining sessions (total contact time 75 minutes), taught by a physiotherapist, with a control group that received asthma education from a nurse. In the Holloway 2007 study, the intervention group completed five 60-minute individual sessions on the Papworth method provided by a respiratory physiotherapist. The control group received no additional treatment. In the Thomas 2009 study, the breathing training group attended three sessions (one small group session and two individual sessions) that provided an explanation of normal breathing and possible effects of abnormal 'dysfunctional breathing'. During individual sessions, participants were taught diaphragmatic and nasal breathing techniques and were encouraged to practise these exercises for at least 10 minutes per day. The control group received three sessions of nurse-provided asthma education. The intervention group in the Grammatopoulou 2011 study received twelve individual breathing retraining sessions, and the control group received usual asthma care. In the study of Prem 2013, 120 participants were divided into three groups: Buteyko, yoga and control. Participants assigned to Buteyko or yoga groups received 3 to 5 days of sessions totalling 60 minutes each day. Participants in the control group followed routine physician care involving pharmacological management.

 
Outcomes

The primary outcome in Holloway 2007, Thomas 2009, Bidwell 2012 and Prem 2013 was quality of life, although different instruments (SGRQ in Holloway 2007 and Bidwell 2012, and AQLQ in Thomas 2009 and Prem 2013) were used. Asthma symptoms as measured by the Asthma Control Test score were the main outcome in Grammatopoulou 2011. In Vempati 2009, pulmonary function was the primary outcome.

Secondary outcomes were asthma symptom and lung function in Holloway 2007 and Thomas 2009. Asthma symptoms were measured by the Nijmegen questionnaire in Holloway 2007 and by the Asthma Control Questionnaire in Thomas 2009. In Grammatopoulou 2011, secondary outcomes were quality of life (as measured by the Short Form (SF)-36 v2 Health Survey) and lung function. In Vempati 2009, the secondary outcome was quality of life (as measured by the AQLQ).

In the other included trials, primary and secondary outcomes were not specified, but the authors reported several main outcome measures, including pulmonary function (Fluge 1994; Sodhi 2009), asthma symptoms (Girodo 1992), number of acute exacerbations and pulmonary function (Nagarathna 1985), quality of life and asthma symptoms (Thomas 2003), asthma symptom and lung function (Vedanthan 1998), and lung function and quality of life (Singh 2012).

 

Excluded studies

After the full text of potentially eligible trials was retrieved, a total of 43 studies were excluded from the review. Two studies previously included were excluded in the 2012 update (Bowler 1998; Opat 2000). Reasons for exclusion are described in the Characteristics of excluded studies.

 

Risk of bias in included studies

Full details of risk of bias judgments can be found in Characteristics of included studies and in Figure 1.

 FigureFigure 1. Risk of bias summary: review authors' judgements about each risk of bias item for each included study.

 

Allocation

Four studies reported adequate sequence generation and were judged to have low risk of bias (Thomas 2003; Holloway 2007; Grammatopoulou 2011; Prem 2013). Nine studies were reported as randomised but gave no description of the methods used and were therefore judged to be at unclear risk of bias (Nagarathna 1985; Girodo 1992; Fluge 1994; Vedanthan 1998; Sodhi 2009; Thomas 2009; Vempati 2009; Bidwell 2012; Singh 2012).

Thomas 2003 recruited individuals with high Nijmegen scores who were currently being treated for asthma at a general practice. Volunteers were randomly assigned by numbering them alphabetically and using random number tables to assign them to trial groups. In Holloway 2007, randomisation was undertaken by a computer-generated number sequence that assigned consecutive subject ID numbers a 1 or a 2 to denote intervention or a control condition. Random allocation was undertaken with sealed envelopes in Grammatopoulou 2011. In Prem 2013, participants were assigned to three groups (Buteyko, yoga and control) through block randomisation.

Only two trials described adequate allocation concealment and were then judged to have low risk of bias (Grammatopoulou 2011; Prem 2013). In Grammatopoulou 2011, allocation concealment was undertaken with sealed envelopes, and in Prem 2013, the method of allocation was concealed in sequentially numbered, sealed, opaque envelopes. The other eleven studies gave no description of the methods of allocation concealment used and were therefore judged to have unclear risk of bias (Nagarathna 1985; Girodo 1992; Fluge 1994; Vedanthan 1998; Thomas 2003; Holloway 2007; Thomas 2009; Vempati 2009; Sodhi 2009; Bidwell 2012; Singh 2012).

 

Blinding

A study is classed as double-blinded if neither the investigator nor the participant involved knows the identity of the intervention. Blinding reduces bias in a trial. Double-blinding is not possible or practical in these studies. Participants in these trials must know whether or not they are undertaking breathing training or asthma education, as compliance is critical to the study. However, it is possible to blind the assessor who is analysing the results of the trial.

Five trials described that the blinding of participants and personnel was not possible; these studies were judged to have a high risk of bias, as it was determined that the outcomes may be influenced by the lack of blinding (Thomas 2003; Holloway 2007; Thomas 2009; Vempati 2009; Grammatopoulou 2011). Eight studies did not describe blinding of participants and personnel, so they were judged to have an unclear risk of bias (Nagarathna 1985; Girodo 1992; Fluge 1994; Vedanthan 1998; Sodhi 2009; Bidwell 2012; Singh 2012; Prem 2013).

Blinding of outcome assessors was described in five studies (Vedanthan 1998; Thomas 2003; Holloway 2007; Grammatopoulou 2011; Prem 2013). In Grammatopoulou 2011, participants were assessed by the same trained assessor, who was blinded to the participants' treatment allocation. In Thomas 2003, questionnaires completed by the participants were scored by the blinded investigator. In Vedanthan 1998, records of the yoga and control groups were coded during the study period, and the decoded data were unavailable to the principal investigators. In Prem 2013, the parameters were recorded before and after training by a person blinded to the allocation of groups. Eight studies did not describe blinding of outcome assessment, so they were judged to have an unclear risk of bias (Nagarathna 1985; Girodo 1992; Fluge 1994; Thomas 2003; Vempati 2009; Sodhi 2009; Bidwell 2012; Singh 2012).  

 

Incomplete outcome data

Two studies did not describe the occurrence of withdrawals and dropouts and were judged to be at unclear risk of bias (Girodo 1992; Sodhi 2009). The study of Nagarathna 1985 affirmed that in total 25 participants dropped out of the study. However, this study was judged to have an unclear risk of bias because it did not describe how many participants dropped out of the study in each group (intervention and control). In three studies, no withdrawals or dropouts were reported; these studies were judged to have a low risk of bias (Vedanthan 1998; Grammatopoulou 2011; Bidwell 2012). Seven studies described withdrawals and dropouts and were also judged to have a low risk of bias because the missing outcome data were balanced in numbers across intervention groups (Thomas 2003; Holloway 2007; Thomas 2009; Vempati 2009) or because the reasons for missing outcome data were unlikely to be related to true outcomes (Fluge 1994; Singh 2012; Prem 2013).

 

Selective reporting

Two studies were registered on clinicaltrials.gov, and all of the prespecified primary and secondary outcomes were reported in a prespecified way (Holloway 2007; Vempati 2009). These studies were judged to have a low risk of bias. Six studies adequately reported outcome data for all primary and secondary outcomes as listed in the methods, although the protocol for each study is not available ( Nagarathna 1985; Thomas 2003; Thomas 2009; Sodhi 2009; Grammatopoulou 2011; Singh 2012). Five studies were judged to be at high risk of bias because one or more outcomes of interest in the review were reported incompletely, so that they cannot be entered into a meta-analysis (Girodo 1992; Fluge 1994; Vedanthan 1998; Bidwell 2012; Prem 2013).

 

Other potential sources of bias

We were unable to identify any other potential biases in four studies (Thomas 2003; Holloway 2007; Grammatopoulou 2011; Prem 2013). Nine studies were judged to be at unclear risk of bias, as they did not provide sufficient information to allow assessment of whether an important risk of bias is present (Nagarathna 1985; Girodo 1992; Fluge 1994; Vedanthan 1998; Thomas 2009; Sodhi 2009; Vempati 2009; Bidwell 2012; Singh 2012).

 

Effects of interventions

See:  Summary of findings for the main comparison

 

Breathing exercises versus inactive control

 
Primary outcome: quality of life

Six studies involving 381 participants reported improvement in quality of life in the groups that submitted to breathing exercises (Holloway 2007; Vempati 2009; Grammatopoulou 2011; Bidwell 2012; Singh 2012; Prem 2013). One study (Holloway 2007) reported data at baseline and at 6 and 12 months after baseline; one (Grammatopoulou 2011) at baseline and at 1, 2 and 6 months; and one (Vempati 2009) at baseline and at 2, 4 and 8 weeks. In Bidwell 2012, Singh 2012 and Prem 2013, data were reported at baseline and at post-treatment. Three of these studies (Holloway 2007; Vempati 2009; Prem 2013) were included in the meta-analysis. However, the studies of Vempati 2009 and Prem 2013 assessed quality of life by the AQLQ, and the study of Holloway 2007 assessed this outcome by the SGRQ. When the AQLQ showed the opposite direction of effect to the SGRQ, these questionnaires were analysed separately.

For the outcome 'Change in AQLQ' ( Analysis 1.1), which included the studies of Vempati 2009 and Prem 2013, meta-analysis showed significant differences favouring the breathing exercises group (MD 0.79, 95% CI 0.50 to 1.08). The postintervention values for the AQLQ in the study of Prem 2013 were provided by the author as means and standard deviations.

The statistical analysis for the SGRQ in the study of Holloway 2007 has a P value that has been adjusted for a baseline covariate. However, the adjusted mean difference was not given in this study. Thus, after the adjusted mean difference was calculated, the analysis for the outcome ‘Change in SGRQ’ ( Analysis 1.2)  yielded a P value smaller than the 0.186 reported in the paper (6 months post-baseline), whereas no difference was seen in the final scores analysis (12 months post-baseline).

We were not able to include the other three studies in the meta-analysis (Grammatopoulou 2011; Bidwell 2012; Singh 2012). Of these, Grammatopoulou 2011 showed that the group that performed breathing exercises showed improvement in the physical component of the SF-36 quality of life questionnaire compared with controls in all assessments (2, 3 and 6 months after intervention, with P values of 0.003, 0.0002 and 0.066, respectively). Bidwell 2012 found significant improvement in the three aspects of the SGRQ (symptoms, activity and impact) in the yoga group compared with the control group (P < 0.05). Singh 2012 observed a significant difference favouring the group submitted to the intervention, with a P value ˂ 0.001 for all four domains of the AQLQ.

Holloway 2007 also assessed the Hospital Anxiety and Depression Score (HADS). This study found significantly lower HADS scores in the intervention group than in the control group, with a P value of 0.002 for HADS Anxiety score and of 0.075 for HDAS Depression score at 6 months post-baseline assessment. At 12 months post-baseline assessment, significant differences favoured the intervention group, with P = 0.772 for the HADS Anxiety score and P < 0.001 for the HADS Depression score.

 
Secondary outcome: asthma symptoms

Five studies involving 331 participants reported asthma symptoms (Girodo 1992; Vedanthan 1998; Holloway 2007; Grammatopoulou 2011; Prem 2013). Meta-analysis was possible for two studies for this outcome (Holloway 2007; Grammatopoulou 2011) ( Analysis 1.3; Figure 2). Assessment of heterogeneity revealed no significant difference between these two studies (I2 = 0%). Meta-analysis showed significant differences favouring the breathing exercises group (MD -3.22, 95% CI -6.31 to -0.13). The other three studies (Girodo 1992; Vedanthan 1998; Prem 2013) did not report sufficient data to enter the meta-analysis. Of these, one study reported no significant difference in asthma symptoms between yoga and control groups (Vedanthan 1998). Girodo 1992 did not observe significant changes in frequency of symptoms on the Asthma Symptom Checklist in any group. However, this study also reported that significant differences (P < 0.03) favoured the intervention group for attack intensity scores (Girodo 1992). In Prem 2013, the comparison between baseline and postintervention values showed that the Buteyko group had better trends toward improvement in total Asthma Control Questionnaire (ACQ) score (P = 0.001) than the pranayama (P = 0.356) and control groups (P = 0.383). The study of Prem 2013 did not provide between-group analyses for this outcome.

 FigureFigure 2. Forest plot of comparison: 1 Breathing exercises versus inactive control, outcome: 1.3 Asthma symptoms.

 
Secondary outcome: number of acute exacerbations

Only one study reported this outcome (Nagarathna 1985). Over two weeks, the intervention group involving 53 participants attended a daily yoga programme lasting two and a half hours. Comparison between the two groups (yoga and control) showed significant improvement (P < 0.005) in the number of exacerbations in the group that received the intervention (Nagarathna 1985). 

 
Secondary outcome: physiological measures

Six studies involving 462 participants reported improvement in spirometry in the groups that performed the intervention (Nagarathna 1985; Sodhi 2009; Vempati 2009; Grammatopoulou 2011; Bidwell 2012; Prem 2013). Four studies did not show significant differences in this outcome (Fluge 1994; Vedanthan 1998; Holloway 2007; Singh 2012). Only two of the ten studies (Sodhi 2009; Vempati 2009) were included in the meta-analysis ( Analysis 1.4,  Analysis 1.5,  Analysis 1.6,  Analysis 1.7;  Analysis 1.8). However, because of the substantial heterogeneity indicated by an I2 statistic greater than 50% for all variables evaluated in spirometry (peak expiratory flow (PEF), forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), FEV1/FVC, air flow in the middle of a forced exhalation (FEF25-75%)), data could not be pooled. This heterogeneity may be attributed to methodological differences in the studies, such as duration of intervention (duration of 45 minutes for 8 weeks vs 4 hours for 2 weeks) for Sodhi 2009 and Vempati 2009, respectively.

Two studies also assessed capnography (Holloway 2007; Grammatopoulou 2011). The study of Holloway 2007 did not find significant differences between intervention and control groups regarding end-tidal carbon dioxide. However, values for relaxed breathing rate over a 10-minute period showed better results in the intervention group than in the control group, with P < 0.001 at 6- and 12-month post-baseline assessments. In the study of Grammatopoulou 2011, the intervention group compared with the control group showed increased end-tidal carbon dioxide (P = 0.002 and 0.003 for 1- and 6-month post-baseline assessments, respectively; P < 0.0001 for 2-month post-baseline assessment). The intervention group showed a decreased respiratory rate compared with the control group (P < 0.0001).

 
Secondary outcomes: inpatient hospitalisation episodes, GP appointments, days off work and subjective evaluation of the intervention

These outcomes were not reported in any of the studies.

 

Breathing exercises versus asthma education

 
Primary outcome: quality of life

Two studies involving 194 participants assessed this outcome (Thomas 2003; Thomas 2009). Both studies had follow-up periods of 1 and 6 months. The study of Thomas 2003 showed a statistically significant improvement (P = 0.018) in overall AQLQ scores in the intervention group compared with the control group after 1 month. After 6 months, only the improvement in the activities domain of the AQLQ was significantly greater in the intervention group than in the control group (P = 0.018). The study of Thomas 2009 showed no significant between-group differences in the four subdomains of the AQLQ at 1-month assessment. At 6 months, significantly greater improvements were found in the intervention group in terms of symptoms (P = 0.01), activities (P = 0.01) and emotions (P = 0.05) domains but not in the environment domain (P = 0.40) compared with controls, with a significant between-groups difference favouring the intervention group (P = 0.01) for the total score (see  Analysis 2.1).

Thomas 2009 also assessed the Hospital Anxiety and Depression Score (HADS). This study found significant reductions in HAD Anxiety and Depression domain scores in both groups 1 month after the intervention, with no significant difference noted between the groups. At the 6-month assessment, significant between-group differences were observed to favour the intervention group for Anxiety score (P = 0.02) and Depression score (P = 0.03).

 
Secondary outcome: asthma symptoms

Two studies involving 194 participants assessed asthma symptoms (Thomas 2003; Thomas 2009). Both studies carried out assessment of symptoms at baseline and 1 month and 6 months after the intervention (Thomas 2003; Thomas 2009). In Thomas 2003, the between-group difference favouring the intervention was statistically significant only after 6 months (P = 0.01). In Thomas 2009, no between-group difference was noted for the ACQ, whereas a statistically significant difference favoured the intervention group at 6-month assessment for the Nijmegen Questionnaire (P = 0.005).

 
Secondary outcome: physiological measures

Only one study assessed spirometric values (Thomas 2009). This study assessed FEV1 by checking that no significant difference (P = 0.07) was evident between the intervention and control groups.

The study of Thomas 2009 also assessed resting end-tidal carbon dioxide concentration, showing that values for this outcome did not change significantly within or between groups.

 
Secondary outcomes: numbers of acute exacerbations, inpatient hospitalisation episodes, GP appointments and days off work and subjective evaluation of the intervention

These outcomes were not reported in these two studies.

 

Discussion

  1. Top of page
  2. Summary of findings    [Explanations]
  3. Background
  4. Objectives
  5. Methods
  6. Results
  7. Discussion
  8. Authors' conclusions
  9. Acknowledgements
  10. Data and analyses
  11. Appendices
  12. What's new
  13. History
  14. Contributions of authors
  15. Declarations of interest
  16. Index terms
 

Summary of main results

This systematic review assessed available evidence for the efficacy of breathing exercises in the treatment of patients with asthma. A total of 13 studies involving 906 participants satisfied the inclusion criteria. Although these studies met the inclusion criteria, they differed significantly in terms of intervention characteristics, such as type of breathing exercise, number of participants, number and duration of sessions, reported outcomes and statistical presentation of data. These differences limited meta-analysis.  

The included studies reported that breathing exercises were well tolerated by participants, and no adverse effects related to the intervention were described, showing that this is a safe non-pharmacological intervention. All eight studies that assessed quality of life reported improvement in this outcome. Improvement in the number of acute exacerbations was observed by the only study that assessed this outcome. Six of seven included studies showed a significant difference favouring breathing exercises for asthma symptoms. Effects on lung function were more variable, with no difference noted in five of the eleven studies that assessed this outcome, although the other six showed a significant difference for this outcome that favoured breathing exercises.

Because the included studies employed different interventions by using different methodologies, meta-analysis for lung function was not possible because of high heterogeneity. For asthma symptoms and changes in AQLQ, meta-analysis showed improvement favouring the group that submitted to breathing exercises. However, each meta-analysis was performed with only two studies.

 

Overall completeness and applicability of evidence

The types of breathing exercises that were related to improvements in quality of life, asthma symptoms and numbers of exacerbations were the Papworth method, Buteyko, diaphragmatic breathing and yoga. The ones that improved lung function were Buteyko, yoga and diaphragmatic breathing. However, the effects seen may represent a combination of many characteristics rather than breathing exercises alone. Some of the included studies involved group sessions in which participants were able to talk to each other and share their experiences. This can also be considered a therapeutic procedure that may affect the sensation of well-being (Evans 1993). Awareness of participation in the study, the sensation of increased care and cure and the specialists’ recommendations to continue regular asthma medication are characteristics that must be considered when the findings of an experimental study are interpreted (Grammatopoulou 2011).

Moreover, asthma severity of participants from the included studies ranged from mild to moderate, so it was not possible to assess the effects of breathing exercises on participants with severe asthma. The samples from studies consisted solely of outpatients. Besides that, four of the eight outcomes proposed by this review were not addressed: inpatient hospitalisation episodes, reduction in general practice (GP) and hospital outpatient appointments, days off work and participants' subjective evaluation of the intervention. 

 

Quality of the evidence

This systematic review was limited by the quality of existing data. Some points must be taken into consideration when the results of this review are analysed, including small sample size and small number of sessions of some studies coupled with limitations in the design and reporting of studies, leading to risk of bias.

In general, the included studies had a small number of participants. The impact of a small sample size on trial results was already reported in a previous study (Moher 1994), which reviewed 383 randomised controlled trials. This study concluded that most trials with negative results did not have large enough sample sizes to detect relative differences. Furthermore, the description of how sample size was determined is recommended by the CONSORT statement (CONSORT 2010). Three of the included studies performed sample size and power calculations: Thomas 2003 (based on AQLQ), Holloway 2007 (based on SGRQ) and Grammatopoulou 2011 (based on ACT). Moreover, the number of sessions involved in these studies was small, given the longer duration of 6 months.

Of the thirteen studies included in the review, only four described the method of random sequence generation and were classified as “low risk of bias”. In addition, the allocation concealment was described in only two studies, which had a low risk of bias for this item. According to Savović 2012, inadequate reporting of trial methods can severely impede assessment of trial quality and of risk of bias in trial results. According to this study, this is a particular problem for the assessment of sequence generation and allocation concealment, which often are not described in trial publications (Savović 2012). In addition, inadequately reported randomisation has been associated with bias in estimating the effectiveness of interventions (Moher 2001).

In a randomised controlled trial, at least three distinct groups (trial participants, trial personnel and outcome assessors) can potentially be blinded (Savović 2012). When a randomised controlled study that involves breathing exercises is conducted, it is not possible for the participants and the personnel to be blinded to the intervention (Holloway 2007). According to Savović 2012, the lack of or unclear double blinding (participants and personnel) can be associated with marked exaggeration of intervention effect estimates.

 

Potential biases in the review process

Although an attempt was made to apply a systematic process for including and excluding studies in this review, besides following the criteria prespecified in the protocol with robust methods for data collection and risk of bias assessment, final decisions are open to interpretation or criticism.

Incomplete outcome data may be considered a potential source of bias of this review. This factor has also limited analysis, as the data from these studies could not be entered into a meta-analysis. Also related to meta-analysis, the subgroup and the sensitivity analysis were not possible because of the impossibility of obtaining sufficient data. This could have showed possible differences in degree of asthma severity, age groups and duration of treatment. Moreover, sensitivity analysis could have identified the influence of some factors (such as trial quality and trial size) on the results, thus revealing a source of the substantial heterogeneity found among studies on lung function.  

 

Agreements and disagreements with other studies or reviews

The current review update included eight new randomised controlled trials and removed two trials that were included in the last published version of this review. In addition, this review brings together trials that were not included in previous systematic reviews (Ernst 2000; Ram 2003). These two reviews assessed the effectiveness of breathing exercises in the management of asthma. The outcomes assessed by Ernst 2000 were asthma symptoms and lung function, and those assessed by Ram 2003 were quality of life, asthma symptoms, number of exacerbations and lung function.

The findings of this review show that, even though outcomes reported by individual trials showed improvement in quality of life indices, asthma symptoms, number of exacerbations and lung function of participants who submitted to breathing exercises, evidence supporting the efficacy of breathing exercises in these outcomes is not sufficient. The systematic review performed by Ernst 2000 affirmed that, on the basis of available data, it was not possible to make firm judgments. Also, this review suggested that breathing techniques seem to have some potential and should be tested rigorously in the future. Similarly, the systematic review performed by Ram 2003 concluded that because evidence available from the small randomised controlled trials included in the review is limited, it was not possible to draw any firm conclusions as to the effectiveness of breathing exercises in the treatment and management of asthma.

It is important to emphasise that, even though the results of this review are consistent with results reported by the two previous systematic reviews (Ernst 2000; Ram 2003), some methodological differences have been noted among these studies. The review of Ernst 2000 was published more than one decade ago. Moreover, this review included two cross-over studies and one study that was performed with children admitted to hospital with acute severe asthma. Ram 2003 included only six studies, which did not involve the same breathing exercise techniques that were examined by the present review, such as the Papworth method.

 

Authors' conclusions

  1. Top of page
  2. Summary of findings    [Explanations]
  3. Background
  4. Objectives
  5. Methods
  6. Results
  7. Discussion
  8. Authors' conclusions
  9. Acknowledgements
  10. Data and analyses
  11. Appendices
  12. What's new
  13. History
  14. Contributions of authors
  15. Declarations of interest
  16. Index terms

 

Implications for practice

This review indicates that breathing exercises are a safe and well-tolerated intervention for people with asthma. Also, meta-analysis of two studies showed that breathing exercises may have positive effects on asthma symptoms and quality of life (more specifically, on AQLQ score). Even though outcomes that were reported from individual trials show that breathing exercises may have a role in the treatment and management of asthma, no conclusive evidence is provided in this review to support or refute the benefits of these techniques in terms of quality of life, asthma symptoms, number of exacerbations and lung function. This is a result of the small number of participants in most of the included studies, the small number of sessions, the methodological differences among included studies, trials with poor methodology and the statistical heterogeneity noted among the studies for three of the four outcomes assessed by meta-analysis. No data are available regarding the effects of breathing exercises on inpatient hospitalisation episodes, reduction in GP and hospital outpatient appointments, days off work and participants' subjective evaluation of the intervention.

 
Implications for research

Well-conducted randomised controlled trials are needed to assess the clinical benefit of breathing exercises in the management of asthma, including those that were not assessed by the studies included in this review such as inpatient hospitalisation episodes, reduction in GP and hospital outpatient appointments, days off work and participants' subjective evaluation of the intervention. Furthermore, in the future, much more attention needs to be paid to good reporting and high-quality study design, including items such as adequate random sequence generation and allocation concealment, blinding of outcome assessor and determination of the trial sample size before the study is begun.

 

Acknowledgements

  1. Top of page
  2. Summary of findings    [Explanations]
  3. Background
  4. Objectives
  5. Methods
  6. Results
  7. Discussion
  8. Authors' conclusions
  9. Acknowledgements
  10. Data and analyses
  11. Appendices
  12. What's new
  13. History
  14. Contributions of authors
  15. Declarations of interest
  16. Index terms

The authors would like to thank Emma Welsh (the Managing Editor of the Cochrane Airways Group) for providing assistance throughout the review process and Elizabeth Stovold (the Trials Search Co-ordinator/Information Specialist of the Cochrane Airways Group) for performing the search. 

We would also like to thank all the authors who responded to our enquiries.

Anne Holland was the Editor for this review. Anne commented critically on the review and assisted the Co-ordinating Editor with signing off on the review for publication.

 

Data and analyses

  1. Top of page
  2. Summary of findings    [Explanations]
  3. Background
  4. Objectives
  5. Methods
  6. Results
  7. Discussion
  8. Authors' conclusions
  9. Acknowledgements
  10. Data and analyses
  11. Appendices
  12. What's new
  13. History
  14. Contributions of authors
  15. Declarations of interest
  16. Index terms
Download statistical data

 
Comparison 1. Breathing exercises versus inactive control

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Change in AQLQ2172Mean Difference (IV, Fixed, 95% CI)0.79 [0.50, 1.08]

    1.1 Buteyko
159Mean Difference (IV, Fixed, 95% CI)0.98 [0.55, 1.41]

    1.2 Pranayama
156Mean Difference (IV, Fixed, 95% CI)0.5 [0.04, 0.96]

    1.3 Yoga
157Mean Difference (IV, Fixed, 95% CI)0.96 [0.28, 1.64]

 2 Change in SGRQ1Mean Difference (IV, Fixed, 95% CI)Subtotals only

    2.1 6 months post baseline
178Mean Difference (IV, Fixed, 95% CI)-5.9 [-12.64, 0.84]

    2.2 12 months post baseline
172Mean Difference (IV, Fixed, 95% CI)-5.00 [-13.97, -0.03]

 3 Asthma symptoms2118Mean Difference (IV, Fixed, 95% CI)-3.22 [-6.31, -0.13]

 4 Lung function (PEF)2Mean Difference (IV, Random, 95% CI)Totals not selected

 5 Lung function (FVC)2Mean Difference (IV, Random, 95% CI)Totals not selected

 6 Lung function (FEV1)2Mean Difference (IV, Random, 95% CI)Totals not selected

 7 Lung function (FEV1/FVC)2Mean Difference (IV, Random, 95% CI)Totals not selected

 8 Lung function (FEF25-75%)2Mean Difference (IV, Random, 95% CI)Totals not selected

 
Comparison 2. Breathing exercises versus asthma education

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Change in AQLQ1Mean Difference (Fixed, 95% CI)0.38 [0.08, 0.68]

 

Appendices

  1. Top of page
  2. Summary of findings    [Explanations]
  3. Background
  4. Objectives
  5. Methods
  6. Results
  7. Discussion
  8. Authors' conclusions
  9. Acknowledgements
  10. Data and analyses
  11. Appendices
  12. What's new
  13. History
  14. Contributions of authors
  15. Declarations of interest
  16. Index terms
 

Appendix 1. Sources and search methods for the Cochrane Airways Group Specialised Register (CAGR)

 

Electronic searches: core databases


DatabaseFrequency of search

CENTRAL (The Cochrane Library)Monthly

MEDLINE (Ovid)Weekly

EMBASE (Ovid)Weekly

PsycINFO (Ovid)Monthly

CINAHL (EBSCO)Monthly

AMED (EBSCO)Monthly



 

 

Handsearches: core respiratory conference abstracts


ConferenceYears searched

American Academy of Allergy, Asthma and Immunology (AAAAI)2001 onwards

American Thoracic Society (ATS)2001 onwards

Asia Pacific Society of Respirology (APSR)2004 onwards

British Thoracic Society Winter Meeting (BTS)2000 onwards

Chest Meeting2003 onwards

European Respiratory Society (ERS)1992, 1994, 2000 onwards

International Primary Care Respiratory Group Congress (IPCRG)2002 onwards

Thoracic Society of Australia and New Zealand (TSANZ)1999 onwards



 

 

MEDLINE search strategy used to identify trials for the CAGR

 

Asthma search

1. exp Asthma/

2. asthma$.mp.

3. (antiasthma$ or anti-asthma$).mp.

4. Respiratory Sounds/

5. wheez$.mp.

6. Bronchial Spasm/

7. bronchospas$.mp.

8. (bronch$ adj3 spasm$).mp.

9. bronchoconstrict$.mp.

10. exp Bronchoconstriction/

11. (bronch$ adj3 constrict$).mp.

12. Bronchial Hyperreactivity/

13. Respiratory Hypersensitivity/

14. ((bronchial$ or respiratory or airway$ or lung$) adj3 (hypersensitiv$ or hyperreactiv$ or allerg$ or insufficiency)).mp.

15. ((dust or mite$) adj3 (allerg$ or hypersensitiv$)).mp.

16. or/1-15

 

Filter to identify RCTs

1. exp "clinical trial [publication type]"/

2. (randomised or randomised).ab,ti.

3. placebo.ab,ti.

4. dt.fs.

5. randomly.ab,ti.

6. trial.ab,ti.

7. groups.ab,ti.

8. or/1-7

9. Animals/

10. Humans/

11. 9 not (9 and 10)

12. 8 not 11

The MEDLINE strategy and RCT filter are adapted to identify trials in other electronic databases.

 

What's new

  1. Top of page
  2. Summary of findings    [Explanations]
  3. Background
  4. Objectives
  5. Methods
  6. Results
  7. Discussion
  8. Authors' conclusions
  9. Acknowledgements
  10. Data and analyses
  11. Appendices
  12. What's new
  13. History
  14. Contributions of authors
  15. Declarations of interest
  16. Index terms

Last assessed as up-to-date: 30 January 2013.


DateEventDescription

30 January 2013New search has been performedLiterature search run.

30 January 2013New citation required and conclusions have changedEight new studies included; two formerly included studies excluded. New author team. Title changed to specify that the review pertains to adults only. Summary of findings table added.



 

History

  1. Top of page
  2. Summary of findings    [Explanations]
  3. Background
  4. Objectives
  5. Methods
  6. Results
  7. Discussion
  8. Authors' conclusions
  9. Acknowledgements
  10. Data and analyses
  11. Appendices
  12. What's new
  13. History
  14. Contributions of authors
  15. Declarations of interest
  16. Index terms

Protocol first published: Issue 4, 1998
Review first published: Issue 3, 2000


DateEventDescription

21 July 2008AmendedConverted to new review format.

16 September 2003New citation required and conclusions have changedSubstantive amendment



 

Contributions of authors

  1. Top of page
  2. Summary of findings    [Explanations]
  3. Background
  4. Objectives
  5. Methods
  6. Results
  7. Discussion
  8. Authors' conclusions
  9. Acknowledgements
  10. Data and analyses
  11. Appendices
  12. What's new
  13. History
  14. Contributions of authors
  15. Declarations of interest
  16. Index terms

Diana Freitas: selected the studies, extracted data, entered data into RevMan, carried out the analysis, interpreted data and drafted the final review.

Elizabeth Holloway: drafted the original review and contributed her clinical expertise.

Selma Bruno: contributed with clinical expertise, carried out the analysis, interpreted data and drafted the final review.

Gabriela Chaves: selected the studies, extracted data, entered data into RevMan, carried out the analysis, interpreted data and drafted the final review.

Guilherme Fregonezi: contributed with clinical expertise and drafted the final review.

Karla Mendonça: coordinated the review, made an intellectual contribution, interpreted data and drafted the final review.

 

Declarations of interest

  1. Top of page
  2. Summary of findings    [Explanations]
  3. Background
  4. Objectives
  5. Methods
  6. Results
  7. Discussion
  8. Authors' conclusions
  9. Acknowledgements
  10. Data and analyses
  11. Appendices
  12. What's new
  13. History
  14. Contributions of authors
  15. Declarations of interest
  16. Index terms

None known.

* Indicates the major publication for the study

References

References to studies included in this review

  1. Top of page
  2. AbstractRésumé
  3. Summary of findings
  4. Background
  5. Objectives
  6. Methods
  7. Results
  8. Discussion
  9. Authors' conclusions
  10. Acknowledgements
  11. Data and analyses
  12. Appendices
  13. What's new
  14. History
  15. Contributions of authors
  16. Declarations of interest
  17. Characteristics of studies
  18. References to studies included in this review
  19. References to studies excluded from this review
  20. References to ongoing studies
  21. Additional references
Bidwell 2012 {published data only}
  • Bidwell AJ, Yazel B, Davin D, Fairchild TJ, Kanaley JA. Yoga training improves quality of life in women with asthma. The Journal of Alternative and Complementary Medicine 2012;18(8):749-55.
Fluge 1994 {published data only}
  • Fluge T, Ritcher H, Fabel H, Zysno E, Wehner E, Wagner IUF. Long term effects of breathing exercises and yoga in patients with asthma. [Langzeiteffekte von Atemgymnastik und Yoga bei Patienten mit Asthma Bronchiale]. Pneumologie 1994;48:485-90.
Girodo 1992 {published data only}
  • Girodo M, Ekstrand KA, Metiver GJ. Deep diaphragmatic breathing: rehabilitation exercises for the asthmatic patient. Archives of Physiology, Medicine and Rehabilitation 1992;73:717-20.
Grammatopoulou 2011 {published data only}
  • Grammatopoulou EP, Skordilis EK, Stavrou N, Myrianthefs P, Karteroliotis K, Baltopoulos G, et al. The effect of physiotherapy-based breathing retraining on asthma control. Journal of Asthma 2011;48(6):593-601.
Holloway 2007 {published data only}
  • Holloway EA, West RJ. Integrated breathing and relaxation training (the Papworth method) for adults with asthma in primary care: a randomised controlled trial. Thorax 2007;62(12):1039–42.
Nagarathna 1985 {published data only}
  • Nagarathna R, Nagendra HR. Yoga for bronchial asthma: a controlled study. British Medical Journal 1985;291:1077-9.
Prem 2013 {published data only}
  • Prem V, Sahoo RC, Adhikari P. Comparison of the effects of Buteyko and pranayama breathing techniques on quality of life in patients with asthma: a randomized controlled trial. Clinical Rehabilitation 2013;27(2):133-41.
Singh 2012 {published data only}
  • Singh S, Soni R, Singh KP, Tandon OP. Effect of yoga practices on pulmonary function tests including transfer factor of lung for carbon monoxide (TLCO) in asthma patients. Indian Journal of Physiology and Pharmacology 2012;56(1):63-8.
Sodhi 2009 {published and unpublished data}
  • Sodhi C, Singh S, Dandona PK. A study of the effect of yoga training on pulmonary functions in patients with bronchial asthma. Indian Journal of Physiology and Pharmacology 2009;53(2):169-74.
Thomas 2003 {published data only}
Thomas 2009 {published data only}
Vedanthan 1998 {published data only}
  • Vedanthan PK, Kasavalu LN, Mutthy KC, Duvall K, Hall MJ, Baker S, et al. Clinical study of yoga techniques in university students with asthma: a controlled study. Allergy and Asthma Proceedings 1998;19(1):3-9.
Vempati 2009 {published data only}
  • Vempati R, Bijlani RL, Deepak KK. The efficacy of a comprehensive lifestyle modification programme based on yoga in the management of bronchial asthma: a randomized controlled trial. BMC Pulmonary Medicine 2009;30(9):10.1186/1471-2466-9-37.

References to studies excluded from this review

  1. Top of page
  2. AbstractRésumé
  3. Summary of findings
  4. Background
  5. Objectives
  6. Methods
  7. Results
  8. Discussion
  9. Authors' conclusions
  10. Acknowledgements
  11. Data and analyses
  12. Appendices
  13. What's new
  14. History
  15. Contributions of authors
  16. Declarations of interest
  17. Characteristics of studies
  18. References to studies included in this review
  19. References to studies excluded from this review
  20. References to ongoing studies
  21. Additional references
Aleksandrov 1990 {published data only}
  • Aleksandrov. [Russian]. Terapevticheskii Arkhiv 1990.
Anonymous 1968 {published data only}
Asher 1990 {published data only}
Berlowitz 1995 {published data only}
Bobokhodzhaev 1984 {published data only}
  • Bobokhodzhaev II, Rudoi DG, Bobkhodzhaev OI, Kovaleva IF, Vlasova IF. Effectiveness of the early inclusion of physical methods in the combined therapy of bronchial asthma [Russian]. Voprosy Kurortologii, Fizioterapii i Lechebnoi Fizicheskoi Kultury 1984;1:58-9.
Bowler 1998 {published data only}
  • Bowler SD, Green A, Mitchell CA. Buteyko breathing techniques in asthma: a blinded randomised controlled trial. The Medical Journal of Australia 1998;169(11-12):575-8.
Cambach 1997 {published data only}
  • Cambach W, Chadwick-Straver RVM, Wagenaar RC, van Keimpema ARJ, Kemper HCG. The effects of a community-based pulmonary rehabilitation programme on exercise tolerance and quality of life: a randomized controlled trial. European Respiratory Journal 1997;10:104-13.
Cambach 1999 {published data only}
  • Cambach W, Wagenaar RC, Koelman TW, van Keimpema T, Kemper HCG. The long-term effects of pulmonary rehabilitation in patients with asthma and chronic obstructive pulmonary disease: a research synthesis.. Archives of Physical Medicine Rehabilitation 1999;80:103-11.
Coll 1994 {published data only}
  • Coll R, Tello A. Yoga in bronchial asthma letter [Yoga en el asma bronquial]. Archivos de Bronconeumologia 1994;30(7):369.
Cooper 2003 {published data only}
  • Cooper S, Oborne J, Newton S, Harrison V, Thompson Coon J, Lewis S, et al. Effect of two breathing exercises (Buteyko and pranayama) in asthma: a randomised controlled trial. Thorax 2003;58(8):674-9.
Cowie 2008 {published data only}
  • Cowie RL, Conley DP, Underwood MF, Reader PG. A randomised controlled trial of the Buteyko technique as an adjunct to conventional management of asthma. Respiratory Medicine 2008;102(5):726-32.
Emtner 1998 {unpublished data only}
  • Emtner M. Rehabilitation of adults with asthma. Doctoral Dissertation, Uppsala University Library, 1998.
Erskine 1979 {published data only}
Falkenbach 1993 {published data only}
  • Falkenbach A, Kirchner P, Richter R, Kaiser C, Schultze-Werninghaus G, Meier-Sydow J. The influence of a comprehensive respiratory therapy and educational program on the symptoms during metacholine-induced acute airway obstruction in asthmatic adults. European Journal of Physical Medicine and Rehabilitation 1993;3(3):95-100.
Gallefoss 1999 {published data only}
  • Gallefoss F, Bakke P S, Kjaersgaard P. Quality of life assessment after patient education in a randomised controlled study on asthma and chronic obstructive pulmonary disease. American Journal Respiratory Critical Care Medicine 1999;159:812-7.
Gosselink 1993 {published data only}
  • Gosselink HAAM, Wagenaar RC. Efficacy of breathing exercises in chronic obstructive pulmonary disease and asthma. Journal of Rehabilitation Sciences 1993;6:66-79.
Holmes 1990 {published data only}
  • Holmes P. An air of hope. Nursing Times 1990;86(33):21.
Joseph 1999 {published data only}
  • Joseph CLM, Foxman B, Leickly FE, Peterson E. Ownby D. Sensitivity and specificity of asthma definitions and symptoms used in a survey of childhood asthma. Journal of Asthma 1999;36(7):565-73.
Khanam 1996 {published data only}
  • Khanam AA, Sachdevaq U, Guleria R, Deepak KK. Study of pulmonary and autonomic functions of asthma patients after yoga training. Indian Journal of Physiology and Pharmacology 1996;40(4):318-24.
Kotses 1978 {published data only}
Kurabayashi 1998 {published data only}
  • Kurabayashi H, Machida I, Handa H, Akiba T, Kubota K. Comparison of three protocols for breathing exercises during immersion in 38C water for chronic obstructive pulmonary disease. American Journal of Physical Medicine Rehabilitation 1998;77(2):145-8.
Lacasse 1997 {published data only}
Loew 1996 {published data only}
  • Loew TH, Siegfried W, Martus P, Tritt K, Hahn EG. 'Functional relaxation' reduces acute airway obstruction in asthmatics as effectively as inhaled terbutaline. Psychotherapy and Psychosomatics 1996;65:124-8.
Manocha 2002 {published data only}
Mass 1991 {published data only}
  • Mass R, Harden H, Leplow B, Wessel M, Richter R, Dahme B. A device for functional residual capacity controlled biofeedback of respiratory resistance [Ein Messaufbau zur Ruckmeldung des Atemwiderstandes unter Kontrolle der funktionellen Residualkapazitat]. Biomedizinische Technik 1991;36(4):78-85.
McFadden 1986 {published data only}
McHugh 2003 {published data only}
  • McHugh P, Aitcheson F, Duncan B, Houghton F. Buteyko Breathing Technique for asthma: an effective intervention. The New Zealand Medical Journal 2003;116(1187):U710.
Mussell 1986 {published data only}
Opat 2000 {published data only}
Paleev 1988 {published data only}
  • Paleev. [Russian]. Klinicheskaia Meditsina 1988.
Pryor 1979 {published data only}
  • Pryor J, Webber BA. An evaluation of the forced expiration technique as an adjunct to postural drainage. Physiotherapy 1979;65(10):304-7.
Redchits 1986 {published data only}
  • Redchits IV, Treumova SI. Effectiveness of the differential treatment of bronchial asthma patients on the southern coast of the Crimea [Russian]. Voprosy kurortologii, fizioterapii, i lechebnoi fizicheskoi kultury 1986;Jul-Aug(4):54-56.
Sabina 2005 {published data only}
  • Sabina AB, Williams A-L, Wall HK, Bansal S, Chupp G, Katz DL. Yoga intervention for adults with mild-to-moderate asthma: a pilot study. Annals of Allergy, Asthma, & Immunology 2005;94(5):543-8.
Saxena 2009 {published data only}
  • Saxena T, Saxena M. The effect of various breathing exercises (pranayama) in patients with bronchial asthma of mild to moderate severity. International Journal of Yoga 2009;2(1):22-5.
Schulze 2000 {published data only}
  • Schulze J, Riel B, Fischer S, Lecheler J, Hofmann D. Improvement of the quality of life by asthma training [Verbesserung der Lebensqualität durch Asthmaschulung]. Pravent-Rehabil 2000;12(3):91-8.
Shaw 2011 {published data only}
  • Shaw BS, Shaw I. Static standing posture and pulmonary function in moderate-persistent asthmatics following aerobic and diaphragmatic breathing training. Pakistan Journal of Medical Sciences 2011;27(3):549-52.
Singh 1987 {published data only}
Singh 1990 {published data only}
Slader 2006 {published data only}
  • Slader CA, Reddel HK, Spencer LM, Belousova EG, Armour CL, Bosnic-Anticevich SZ, et al. Double blind randomised controlled trial of two different breathing techniques in the management of asthma. Thorax 2006;61(2):651-6.
Smyth 1999 {published data only}
  • Smyth JM. Soeffer MH, Hurewitz A, Stone AA. The effect of tape recorded relaxation training on well being symptoms, and peak expiratory flow rate in adult asthmatics: a pilot study. Psychology and Health 1999;14:487-501.
Tandon 1978 {published data only}
van der Schans 1997 {published data only}
  • van der Schans CP, de Jong W, de Vries G, Postma DS, Koeter GH, van der Mark TW. Respiratory muscle activity and pulmonary function during acutely induced airways obstruction. Physiotherapy Research International 1997;2(3):167-94.
Weiner 1992 {published data only}
Wilson 1975 {published data only}
  • Wilson AF, Honsberger R, Chiu JT, Novey HS. Transcendental meditation and asthma. Respiration 1975;32:74-80.

References to ongoing studies

  1. Top of page
  2. AbstractRésumé
  3. Summary of findings
  4. Background
  5. Objectives
  6. Methods
  7. Results
  8. Discussion
  9. Authors' conclusions
  10. Acknowledgements
  11. Data and analyses
  12. Appendices
  13. What's new
  14. History
  15. Contributions of authors
  16. Declarations of interest
  17. Characteristics of studies
  18. References to studies included in this review
  19. References to studies excluded from this review
  20. References to ongoing studies
  21. Additional references
Murthy 2010 {unpublished data only}
  • Effect of naturopathy interventions in bronchial asthma . Ongoing study 01/10/2009 (date of first enrolment).
Thomas 2011 {unpublished data only}
  • Study of the effectiveness of breathing training exercises taught by a physiotherapist by instructional videos/DVDs/Internet download or by face-to-face sessions in the management of asthma in adults. Ongoing study 01/11/2011.

Additional references

  1. Top of page
  2. AbstractRésumé
  3. Summary of findings
  4. Background
  5. Objectives
  6. Methods
  7. Results
  8. Discussion
  9. Authors' conclusions
  10. Acknowledgements
  11. Data and analyses
  12. Appendices
  13. What's new
  14. History
  15. Contributions of authors
  16. Declarations of interest
  17. Characteristics of studies
  18. References to studies included in this review
  19. References to studies excluded from this review
  20. References to ongoing studies
  21. Additional references
Allen 2012
  • Allen JC, Seidel P, Schlosser T, Ramsay EE, Ge Q, Ammit AJ. Cyclin D1 in ASM cells from asthmatics is insensitive to corticosteroid inhibition. Journal of Allergy (Cairo) 2012:Article ID 307838. [DOI: 10.1155/2012/307838]
Arun 2012
  • Arun JJ, Lodha R, Kabra SK. Bronchodilatory effect of inhaled budesonide/formoterol and budesonide/salbutamol in acute asthma: a double-blind, randomized controlled trial. BMC Pediatrics 2012;12:21.
Bateman 2008
  • Bateman ED, Hurd SS, Barnes PJ, Bousquet J, Drazen JM, FitzGerald M. Global strategy for asthma management and prevention: GINA executive summary. The European Respiratory Journal 2008;31(1):143-78.
Blanc 2001
  • Blanc PD, Trupin L, Earnest G, Katz PP, Yelin EH, Eisner MD. Alternative therapies among adults with a reported diagnosis of asthma or rhinosinusitis: data from a population-based survey. Chest 2001;120(5):1461-7.
Bousquet 2010
  • Bousquet J, Mantzouranis E, Cruz AA, Aït-Khaled N, Baena-Cagnani CE, Bleecker ER, et al. Uniform definition of asthma severity, control, and exacerbations: document presented for the World Health Organization Consultation on Severe Asthma. The Journal of Allergy and Clinical Immunology 2010;126(5):926-38.
Brightling 2012
Bruton 2005a
Bruton 2005b
Burgess 2011
  • Burgess J, Ekanayake B, Lowe A, Dunt D, Thien F, Dharmage SC. Systematic review of the effectiveness of breathing retraining in asthma management. Expert Review of Respiratory Medicine 2011;5(6):789-807.
Cluff 1984
  • Cluff RC. Chronic hyperventilation and its treatment by physiotherapy. Journal of the Royal Society of Medicine 1984;10(77):855-62.
CONSORT 2010
  • Schulz KF, Altman DG, Moher D, for the CONSORT Group. CONSORT 2010 Statement: updated guidelines for reporting parallel group randomised trials. BMC Medicine 2010;8:18.
Dennis 2012
Eisner 2012
  • Eisner MD, Yegin A, Trzaskoma B. Severity of asthma score predicts clinical outcomes in patients with moderate to severe persistent asthma. Chest 2012;141(1):58-65.
Ernst 2000
Evans 1993
Giavina-Bianchi 2010
  • Giavina-Bianchi P, Aun MV, Bisaccioni C, Agondi R, Kalil J. Difficult-to-control asthma management through the use of a specific protocol. Clinics 2010;65(9):905-18.
GINA 2011
  • Global Initiative for Asthma. Global strategy for asthma management and prevention, 2011. www.ginasthma.com (accessed August 2012).
Higgins 2011a
  • Higgins JPT, Deeks JJ. Chapter 7: Selecting studies and collecting data. In: Higgins JPT, Green S (editors). Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 [updated March 2011]. The Cochrane Collaboration, 2011. www.cochrane-handbook.org.
Higgins 2011b
  • Higgins JPT, Altman DG, Sterne JAC. Chapter 8: Assessing risk of bias in included studies. In: Higgins JPT, Green S (editors). Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 [updated March 2011]. The Cochrane Collaboration, 2011. www.cochrane-handbook.org.
Higgins 2011c
  • Deeks JJ, Higgins JPT, Altman DG. Chapter 9: Analysing data and undertaking meta-analyses. In: Higgins JPT, Green S [editors]. Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 [updated March 2011]. The Cochrane Collaboration, 2011. www.cochrane-handbook.org.
Higgins 2011d
  • Sterne JAC, Egger M, Moher D. Chapter 10: Addressing reporting biases. In: Higgins JPT, Green S (editors). Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 [updated March 2011]. The Cochrane Collaboration, 2011. www.cochrane-handbook.org.
Holgate 2009
Holloway 1994
  • Holloway EA. The Role of the physiotherapist. In: Timmons BH, Ley R editor(s). Behavoural and Psychological Approaches to Breathing Disorders. First Edition. New York: Plenum Press, 1994:157-75.
Innocenti 1993
  • Innocenti DM. In: Pryor J, Webber B editor(s). Physiotherapy in Respiratory Care & Cardiac Rehabilitation. London: Churchill Livingstone, 1993.
Juniper 2004
  • Juniper EF, Wisniewski ME, Cox FM, Emmett AH, Nielsen KE, O'Byrne PM. Relationship between quality of life and clinical status in asthma: a factor analysis. The European Respiratory Journal 2004;23(2):287-91.
Laffey 2002
Lum 1994
  • Lum LC. Hyperventilation Syndromes. In: Ley R, Timmons BH editor(s). Behavoural and Psychological Approaches to Breathing Disorders. First Edition. New York: Plenum Press, 1994:113-23.
McCarney 2012
Moher 1994
  • Moher D, Dulberg CS, Wells GA. Statistical power, sample size, and their reporting in randomized controlled trials. JAMA 1994;272(2):122-4.
Moher 2001
Ram 2003
Ram 2009
  • Ram FSF, Wellington SR, Barnes NC. Inspiratory muscle training for asthma. Cochrane Database of Systematic Reviews 2009, Issue 4. [DOI: 10.1002/14651858.CD003792]
RevMan 2011
  • Copenhagen: The Nordic Cochrane Centre, The Cochrane Collaboration. Review Manager (RevMan). 5.1. Copenhagen: The Nordic Cochrane Centre, The Cochrane Collaboration, 2011.
Rimington 2001
Savović 2012
  • Savović J, Jones H, Altman D, Harris R, Jni P, Pildal J, et al. Influence of reported study design characteristics on intervention effect estimates from randomised controlled trials: combined analysis of meta-epidemiological studies. Health Technology Assessment 2012;16(35):1-82.
Singh 1990a
Sveum 2012
  • Sveum R, Bergstrom J, Brottman G, Hanson M, Heiman M, Johns K, et al. Institute for Clinical Systems Improvement. Diagnosis and Management of Asthma. Updated July 2012. https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&ved=0CFQQFjAE&url=https%3A%2F%2Fwww.icsi.org%2F_asset%2Frsjvnd%2FAsthma.pdf&ei=sRZAUvu3Mci10wXg2oCYCA&usg=AFQjCNGUOXZNQ3xBFXDTa5oQ931Wg9LELg&bvm=bv.52434380,d.d2k&cad=rja (accessed 23 September 2013).
Taylor 2008
Thomas 2001
To 2012
  • To T, Stanojevic S, Moores G, Gershon AS, Bateman ED, Cruz AA, et al. Global asthma prevalence in adults: findings from the cross-sectional world health survey. BMC Public Health 2012;12:204.
van den Elshout 1991
Welsh 2011
Wolf 2008
  • Wolf F, Guevara JP, Grum CM, Clark NM, Cates CJ. Educational interventions for asthma in children. Cochrane Database of Systematic Reviews 2008, Issue 4. [DOI: 10.1002/14651858.CD000326]
Zhang 2010