Description of the condition
Asthma is a common chronic inflammatory disorder characterized by hypersensitivity of the airways and reversible, episodic airway obstruction (Miller 2001). Typical symptoms of asthma include wheezing, coughing, chest tightness and dyspnoea (i.e. shortness of breath). Many patients with asthma also have so-called 'somatopsychic imbalance' in such forms as suppressed emotion, anxiety and heightened self-consciousness together with muscle tension, both generalized and localized (Goyeche 1982). The asthma attacks and the panic or anxiety associated with the attacks can affect the lifestyle (e.g. social activities), wellbeing, and perceived health status of patients with asthma to varying degrees, making improving quality of life an important issue in asthma management. Over the past decade, the prevalence of asthma has dramatically increased. Globally, asthma affects about 300 million people, and this figure continues to rise (Masoli 2004; ISAAC 2006). Asthma represents a huge economic burden on society. In the United States of America (USA), the management of asthma costs more than US dollars (USD) 12.7 billion per year (Weiss 2001). In Germany, Switzerland and Singapore, national studies have estimated the annual total costs for asthma to be USD4.43 billion, USD1.41 billion and USD49 million respectively (Chew 1999; Stock 2005; Szucs 1999).
Current guidelines for asthma treatment recommend a severity-based, stepwise approach (Global Initiative for Asthma 2011). Common agents to treat people with asthma include inhaled corticosteroids and long-acting beta agonists (Becker 2003). For severe cases, additional controller medications such as anti-leukotrienes, oral corticosteroids and anti-IgE therapy are recommended (Global Initiative for Asthma 2011; Peters 2006). However, somatopsychic imbalance has been seldom addressed by traditional drug treatments, pointing to the need for a holistic, somatopsychic therapy for people with asthma (Goyeche 1982).
Description of the intervention
Yoga originated from ancient India and remains an important element of India's diverse culture. Common components of yoga include breathing exercises (pranayama), postures (asanas) and meditation (dhyana) (Riley 2004). As different combinations of and variations in components could represent a 'new' type of yoga, it is hard to tell exactly how many types of yoga are being practiced around the world. To our knowledge, types of yoga include but are not limited to the following: aerial yoga, Ananda yoga, Anusara yoga, Ashtanga (or Astanga) yoga, Bhakti yoga, Bikram yoga (hot yoga), Chair yoga, Forrest yoga, Hatha yoga, ISHTA (Integral Science of Hatha and Tantric Arts), Iyengar yoga, Jivamukti yoga, Jnana yoga, Kali Ray TriYoga, Karma yoga, Kripalu, Kriya yoga, Kundalini yoga, Mantra yoga, Moksha, Power yoga, prenatal yoga, Purna yoga (integral yoga), Raja yoga, Restorative yoga, Sahaja yoga, Satyananda yoga, Sivananda yoga, stand-up paddle yoga, Svaroopa yoga, Swara yoga, Tibetan yoga, Viniyoga yoga, Vinyasa yoga and White Lotus yoga (about.com; dailycupofyoga.com; iloveindia.com; matsmatsmats.com; mindbodygreen.com; spine-health.com; yogajournal.com; yogapoint.com). It appears that there has been no estimate of the proportion of each type of yoga taught by practitioners worldwide. According to the polls conducted by Yoga Journal, the most commonly-practiced yoga in the USA is Iyengar (43.6%), followed by Ashtanga (29.1%), Power yoga (15.9%), Bikram (7.3%), Kundalini (7.1%), Sivananda (6.4%), Viniyoga (5.7%) and other (Lamb 2006). The practice of yoga seeks to attain a perfect integration of body, mind and spirit (Anand 1991; Kappmeier 2006).
Yoga has been gaining in global popularity, partly due to its reputed physical and psychological benefits. Currently available data (which are not necessarily accurate) show that there were about 16 million yoga practitioners in the USA alone (Harris Interactive Service Bureau 2008), more than 3 million adult yoga practitioners in Germany in 2004, approximately 2 million (3% of the total population) in Great Britain in 2004, less than 1 million (around 8% of the total population) in Taiwan in 2005, 0.5 to 1 million (0.4% to 0.8% of the total population) in Japan in 2004, and 454,000 (2.8% of the total population) in Australia in 2007 (Lamb 2006; Penman 2008). The International Yoga Federation once estimated that there were about 300 million yoga practitioners worldwide (Lamb 2006).
Yoga practice often involves a financial cost, such as the expense of attending classes, and purchasing props, clothing, books, magazines, DVDs and yoga mats. It has been reported that practitioners spend nearly USD6 billion on yoga classes and products each year in the USA (Harris Interactive Service Bureau 2008). An Australian national survey showed that 98.65 dollars were spent on yoga practice per participant per month on average, amounting to a total of 537.4 million dollars per year for all participants in Australia (Penman 2008). According to the 'conservative estimate' by a 2002 article in Yoga Journal, a yoga practitioner spends USD1,500 on yoga practice yearly (Lamb 2006).
How the intervention might work
As a holistic therapy, yoga practice contains no asthma-specific posture or breathing exercises (Goyeche 1982). The exact mechanism by which yoga may affect asthma symptoms is not fully understood (Vernpati 2009). However, several explanations have been proposed.
The first has to do with the breathing pattern in yoga practice. One trigger of asthma attacks is frictional stress in airways, which could damage the airway wall, affect the dynamics of airway smooth muscle and result in the mast cell degranulation (Singh 1990; Solway 1997; Chowdhary 1999). Some studies have shown that the tidal volume and breathing rate decrease during yoga practice (Kesterson 1989; Sudsuang 1991), which may interfere with the process that triggers asthma attacks. Empirically, randomised controlled trials conducted in patients with asthma have demonstrated that specific breathing exercises or techniques could help reduce acute exacerbations and rescue bronchodilator use as compared with no intervention, and could significantly improve quality of life as compared with asthma education (Fluge 1994; Bowler 1998; Opat 2000; Thomas 2003). However data were insufficient to draw conclusions to this effect in a Cochrane review comparing breathing exercises with usual care or asthma education control (Holloway 2004). Therefore, yoga practice involving breathing techniques may have some impact on asthma symptoms. Breathing exercises in yoga practice could help release suppressed emotion, reduce anxiety and self-consciousness, and relax tense muscles (Goyeche 1982).
Secondly, certain yoga postures may help expand the chest and increase breath-holding time as well as vital capacity (Goyeche 1982). This, logically, could have some effect on the lung function of patients with asthma.
Thirdly, by practicing yoga people with asthma may achieve a sense of relaxation and a positive mood, thus reducing the autonomic arousal factors like mast cell activation (Goyeche 1982; Manocha 2002; Vernpati 2009). Meditation, a common component of yoga, may even help yoga practitioners reach a state of complete mental silence ('Sahaja' in Sanskrit), which advocates of yoga consider to be an innately therapeutic process beneficial to people with chronic diseases, including asthma. Meditation may also help the control and feedback of respiratory muscles which would be adversely affected by asthma attacks (Nayak 2004).
Why it is important to do this review
Previous literature indicates that yoga might be applied for obstructive pulmonary disease (Donesky-Curenco 2009), pulmonary tuberculosis (Visweswaraiah 2004), hypertension (Patel 1975; Sundar 1984; van Montfrans 1990), myocardial infarction (Bulavin 1993), chronic back pain (Groessl 2008; Tekur 2008), osteoarthritis (Bukowski 2007) and other medical disorders (Jain 1993; Ramaratnam 2000; Culos-Reed 2006; DiStasio 2008). However, as the National Center for Complementary and Alternative Medicine stated, "there is not enough evidence to support the use of any complementary health practices for the relief of asthma" (NCCAM 2012). A number of clinical trials have been carried out to evaluate the efficacy of yoga for asthma. Some of them suggested that yoga may enhance pulmonary function and reduce airway hyper-responsiveness, emotional stress, and asthma attacks (Nagarathna 1985; Sodhi 2009; Vernpati 2009), while others showed that yoga conferred rather limited or even no benefit (Manocha 2002; Sabina 2005). Such information may confuse asthma patients when they are deciding whether or not to spend time and money on practicing yoga. To better understand current evidence and investigate potential sources of heterogeneity between studies, we propose to conduct the present Cochrane review.
To assess the effects of yoga on people with asthma.
Criteria for considering studies for this review
Types of studies
Randomized controlled trials.
Types of participants
Patients with asthma of any duration and severity, irrespective of age, gender, ethnicity or language spoken.
Types of interventions
We will include studies if they state that the intervention was yoga as compared with sham intervention or no intervention. The intervention should last for at least two weeks, as a randomised controlled trial showed that two weeks were sufficient for yoga-based interventions to reach efficacy in the management of bronchial asthma (Vernpati 2009). We will use the following comparisons:
- Yoga versus usual care (or no intervention)
- Yoga versus sham intervention
Types of outcome measures
The outcomes of this review are listed below. Our pilot search suggests that relevant trials usually report only a selection of these outcome measures. Therefore, studies will not be included or excluded on the basis of reported outcomes.
- Self-reported quality of life measured by validated questionnaires (e.g. asthma quality of life questionnaire (AQLQ));
- Self-reported symptom scores (e.g. asthma symptom scale)
- Asthma control (e.g. Asthma Control Test)
- Lung function, such as forced expiratory volume in one second (FEV1), peak expiratory flow rate (PEFR), forced vital capacity (FVC), etc.
- Asthma medication usage (e.g. frequency of inhaler use)
- Adverse events
We chose quality of life and symptoms as the primary outcomes of our review because they are patient important outcomes (Ozgen Alpaydin 2011). The physiological measures of lung function and medication usage may indirectly reflect the potential benefit of yoga, while adverse events indicate the related risk. We will include studies of at least one month follow-up and we will use the outcomes measured at the end of the study.
Search methods for identification of studies
We will identify trials 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 handsearching of respiratory journals and meeting abstracts (please see Appendix 1 for further details). We will search all records in the CAGR coded as 'asthma', using the following terms:
yog* OR meditat* OR relax* OR hatha OR ashtanga OR bikram OR iyengar OR kripalu OR kundalini OR sivananda OR vinyasa OR raja OR radja OR bhakti OR jnana OR kriya OR karma OR yama OR niyama OR asana OR pranayama OR pratyahara OR dharana OR dhyana OR samadhi OR bandha OR mudra.
An additional search of the Alternative Medicine Electronic Database (AMED) will be conducted using the strategy in Appendix 2. We will also search ClinicalTrials.gov using the above terms related to yoga as 'Search Terms', and 'asthma' as Conditions' under the 'Advanced Search' tab. We will search the WHO ICTRP search portal (http://apps.who.int/trialsearch/Default.aspx) using the above terms in the 'Title', and 'asthma' as 'Conditions' under the 'Advanced Search' tab. All databases will be searched from their inception to the present, and there will be no restriction on language of publication.
Searching other resources
We will check the reference lists of all primary studies and review articles for additional references. We will contact authors of identified trials and ask them to identify other published and unpublished studies. We will also contact experts in the field.
Data collection and analysis
Selection of studies
Two review authors (YJQ, HYF) will independently screen titles and abstracts for inclusion of all the potential studies we identify as a result of the search and code them as 'retrieve' (eligible or potentially eligible/unclear) or 'do not retrieve'. We will retrieve the full-text study reports/publication and two review authors (YJQ, HYF) will independently screen the full-text and identify studies for inclusion, and identify and record reasons for exclusion of the ineligible studies. We will resolve any disagreement through discussion or, if required, we will consult a third person (TJL). We will identify and exclude duplicates and collate multiple reports of the same study so that each study rather than each report is the unit of interest in the review. We will record the selection process in sufficient detail to complete a PRISMA flow diagram and 'Characteristics of excluded studies' table.
Data extraction and management
We will design and pilot test a standard form for data extraction. We will extract information on study characteristics (title, authors, publication date, participants, interventions, outcomes), methods (randomisation, blinding, follow-up, data analysis, etc.), and relevant outcome data. Again, this process will be performed independently by two authors and inconsistencies will be resolved by discussion. If necessary, we will contact authors of the original study to obtain additional data and/or to confirm methodological aspects of the study.
Assessment of risk of bias in included studies
Two review authors (WXY, MC) will independently assess the risk of bias for each included study using the criteria outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). Any disagreement will be resolved by discussion or by involving TJL. We will assess the risk of bias according to the following domains:
- Random sequence generation;
- Allocation concealment;
- Blinding of participants and personnel;
- Blinding of outcome assessment;
- Incomplete outcome data;
- Selective outcome reporting;
- Other bias.
We will grade each potential source of bias as high risk, low risk or unclear.
Measures of treatment effect
For continuous outcome such as FEV1 and AQLQ, we will calculate a mean difference (MD) with 95% confidence interval (95% CI) to denote the treatment effect if the outcome is measured by the same scale in different studies. If the outcome in different studies is measured by different scales, then we will calculate the standardized mean difference (SMD) with 95% CI. For dichotomous outcomes, we will report the treatment effect by risk ratio (RR) with 95% CI.
Unit of analysis issues
We have conducted a pilot search and found that published studies eligible for this review were all individually randomised, parallel trials, without multiple yoga intervention groups. Hence, it seems that unit-of-analysis issues related to cluster-randomized trials, crossover trials and multiple intervention groups are unlikely to arise. We will try to avoid any potential unit-of-analysis error by extracting and analysing the data carefully according to the methods recommended in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011).
Dealing with missing data
We will contact investigators or study sponsors in order to verify key study characteristics and obtain missing numerical outcome data where possible.
Assessment of heterogeneity
We will use the I² statistic to measure heterogeneity among the trials in each analysis. If we identify substantial heterogeneity (I² ≥ 50%) we will explore it by pre-specified subgroup analysis (see Subgroup analysis and investigation of heterogeneity).
Assessment of reporting biases
Where we suspect reporting bias (see 'Selective reporting bias' above), we will attempt to contact study authors asking them to provide missing outcome data. Where this is not possible, and the missing data are thought to introduce serious bias, we will explore the impact of including such studies on the overall assessment of results by a sensitivity analysis. We will visually inspect funnel plots to see if there is possible publication bias.
We plan to perform meta-analysis with Review Manager 5 on each outcome provided that the outcome measures are similar enough and the data reported are sufficient for such an analysis. We will use a fixed-effect model if there is no substantial heterogeneity among studies. Otherwise we will explore the potential source of the heterogeneity by subgroup analysis, or if necessary, use a random-effects model to pool the data. For outcomes for which it is inappropriate or impossible to pool quantitatively , we will conduct descriptive analysis and summarise the findings narratively.
We plan to create a 'Summary of findings' table using the methods and recommendations described in Section 8.5 and Chapter 12 of the Cochrane Handbook (Higgins 2011) and using GRADEpro software. We plan to include the following outcomes in the 'Summary of findings' table: Self-reported quality of life, self-reported symptom scores, lung function, asthma medication usage and adverse events.
Subgroup analysis and investigation of heterogeneity
We plan to carry out the following subgroup analyses:
- Age: adults versus children
- Gender: male versus female
- Ethnicity: Asian versus Caucasian versus Australian versus African
- Severity of asthma: mild versus moderate-to-severe
- The subtype of yoga: yoga that includes breathing exercises versus other types
- Duration of intervention: ≤ 1 month versus 1 to 2 months versus > 2 months
We plan to conduct sensitivity analysis to assess the robustness of the results by excluding the studies at high or unclear risk of bias. For this review, a study will be rated as being 'at high risk of bias' when there is 'high risk of bias' in any of the domains of the Cochrane Collaboration's risk of bias tool, and as being 'at unclear risk of bias' when there is an 'unclear risk of bias' in one or more domains with 'low risk of bias' in all the remaining domains. We note that, as the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011) states, all thresholds for high or low risk are arbitrary, and studies may lie anywhere on the spectrum from 'free of bias' to 'undoubtedly biased'.
We thank Emma Welsh for her editorial assistance and Anne Holland for editing the review. We thank Elizabeth Stovold for her comments on the search strategy.
Appendix 1. Sources and search methods for the Cochrane Airways Group Specialised Register (CAGR)
Electronic searches: core databases
Handsearches: core respiratory conference abstracts
MEDLINE search strategy used to identify trials for the CAGR
1. exp Asthma/
3. (antiasthma$ or anti-asthma$).mp.
4. Respiratory Sounds/
6. Bronchial Spasm/
8. (bronch$ adj3 spasm$).mp.
10. exp Bronchoconstriction/
11. (bronch$ 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.
Filter to identify randomised controlled trials (RCTs)
1. exp "clinical trial [publication type]"/
2. (randomised or randomised).ab,ti.
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.
Appendix 2. AMED search strategy
7. (hatha or ashtanga or bikram or iyengar or kripalu or kundalini or sivananda or vinyasa or raja or radja or bhakti or jnana or kriya or karma or yama or niyama or asana or pranayama or pratyahara or dharana or dhyana or samadhi or bandha or mudra).af.
11. spasm/ or respiratory tract disease/
13. (bronch* adj3 spasm*).af.
15. (bronch* adj3 constrict*).af.
16. Respiratory hypersensitivity/
17. ((bronchial* or respiratory or airway* or lung*) adj3 (hypersensitiv* or hyperreactiv* or allerg* or insufficiency)).af.
18. 1 or 2 or 3 or 4 or 5 or 6 or 7
19. 8 or 9 or 10 or 11 or 12 or 13 or 14 or 15 or 16 or 17
20. 18 AND 19
Contributions of authors
YZY and YJQ drafted the protocol with clinical and methodological input from GYM, MC, and TJL.
Declarations of interest
Sources of support
- None, Not specified.
- None, Not specified.