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O’Connor E, Patnode CD, Burda BU, et al. Breathing Exercises and/or Retraining Techniques in the Treatment of Asthma: Comparative Effectiveness [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US); 2012 Sep. (Comparative Effectiveness Reviews, No. 71.)
This publication is provided for historical reference only and the information may be out of date.
Breathing Exercises and/or Retraining Techniques in the Treatment of Asthma: Comparative Effectiveness [Internet].
Show detailsOverview of Main Findings
Available evidence suggests that selected intensive behavioral approaches that include breathing retraining exercises may improve asthma symptoms and reduce reliever medication use in motivated adults with poorly controlled asthma. This suggestion, however, was based primarily on evidence from small, methodologically limited trials with widely heterogeneous samples. The evidence was further compromised by the relatively short followup and inconsistent outcome reporting (Table 15). Primary outcomes (symptom reduction and reliever medication use) were also self-reported, making them susceptible to social desirability bias. The largest, most coherent body of evidence for a specific breathing training technique assessed hyperventilation reduction techniques and showed they reduced asthma symptoms and reliever medication use.
Table 15
Strength of evidence.
Hyperventilation reduction techniques were not found to improve pulmonary function tests as measured by FEV1 or PEF. Yoga was the only technique with evidence that it may improve pulmonary function and symptoms. However, quality issues in these trials limit confidence in results and applicability to the U.S. health care system was very low. The yoga practiced in these trials was likely more intensive than would available to most patients in the United States, for example 4 hours per day for 2 weeks, or daily 70-minute sessions for 6 months. Additionally, yoga may not have the same cultural significance in the United States as it does in India. Available research on IMT and other breathing retraining techniques was limited to a heterogeneous group of small trials that are best characterized as pilot studies, which provided insufficient evidence to draw conclusions on these interventions’ effectiveness.
Programs that included more hours of contact (e.g., 5 or more hours) and that also offered intervention components beyond breathing retraining or advice appeared more likely to be found effective. Trials that matched treatment groups for number of hours of contact were less likely to show benefit than those providing extra hours of contact for the intervention group. This suggests that generic benefits of therapeutic contact (e.g., empathy, encouragement, and self-monitoring techniques) may be important components of treatment. These observations, however, should be considered hypothesis-generating rather than definitive for numerous reasons, including the lack of accounting for effect size and the high heterogeneity on numerous dimensions in these trials, which precludes clear isolation of the effects of any specific elements. Specific mechanisms of action for breathing training may be less important than enhanced self-efficacy, self-monitoring, and anxiety management.
Although interventions could be quite intensive, there was no evidence that breathing techniques are harmful besides minor annoyances associated with mouth taping. Although asthma medications associated with NAEPP guidelines are generally safe and effective, they can be associated with unpleasant or even harmful side effects,1 so breathing retraining may be worth trying for some patients who are highly motivated to manage asthma symptoms with minimal use of reliever medication. In the United States, results of these trials would likely be most applicable to patients with a high level of motivation, given the fairly high attrition rates in several trials and, in some cases, selected samples.
Evidence was primarily applicable to adults; only a single trial of IMT targeted children (ages 8 to 12 years),65 and only four other trials included people younger than 16 years of age, 50,53,56,58 all addressing hyperventilation reduction training. It is unlikely that many teens were included in these trials, however, since, where it was reported, the average participant age was in the forties in these studies. Subgroup analyses of teens and/or emerging adults were not reported.
Hyperventilation Reduction Breathing Retraining Techniques
Hyperventilation reduction techniques had the best evidence base, with 11 efficacy or comparative effectiveness trials. Almost all trials had very small samples, and all had some methodological limitations. The only relatively large-scale trial of any breathing retraining method (n=600 randomized into three groups) investigated the effects of Buteyko techniques and showed substantially larger reductions in both asthma symptoms and reliever medication use in the treatment group, compared to either of two control groups. Retention in the two control groups in this trial, however, was lower in the two control groups than the Buteyko group (90% retention in the Buteyko group vs. 82% in the intensity-matched group vs. 73% in the low-intensity control group at 6 months).56
Five of the seven trials that compared comprehensive hyperventilation reduction training with a control or placebo reported reductions in asthma symptoms.54–56,59,71 The pooled estimate suggested a large effect on asthma symptoms, although only four trials provided sufficient data to be included in the meta-analysis, and statistical heterogeneity was very high. In general, pooled estimates based on few trials are likely to overestimate true effects,107 and including four trials will provide an estimate that is within 10 percent of the true estimate of effect in only about 50 percent of cases, according to a recent analysis.108 Thus, the pooled estimate in this case may overestimate the true effect. Of the four trials in the meta-analysis, one was the large trial described above and the other three were limited by either low retention,59 no report of pulmonary function testing to confirm asthma,54,59 no report that allocation was concealed,55 and lack of blinding of outcomes assessment.55
Hyperventilation reduction interventions did not show greater reduction in asthma symptoms than interventions involving other breathing techniques. In some cases, both the intervention and controls groups improved, while in others neither group showed improvement.
All but one of the trials that showed improvements in asthma symptoms involved at least 5 hours more of intervention contact for study subjects in the treatment group(s), compared with usual care or control groups. Two trials included additional components not related to breathing.52,55 As hyperventilation reduction techniques required substantial practice on the part of asthma patients, it is not surprising that extra support was important for patients to master the techniques and maintain their use. On the other hand, greater general support could also explain between-group differences.
Most trials (five of the nine trials reporting reliever medication use) showed greater reductions in reliever medication use with hyperventilation reduction breathing training, compared with either a control group or another breathing approach.51,52,56,57,59 In most cases, reductions in bronchodilator use generally amounted to an average of 1.5 to 2.5 puffs per day, apparently almost eliminating the use of bronchodilators in two trials.52,56 In one trial of patients with high medication use (median baseline use was 8.5 to 9.5 puffs per day), intervention participants reduced reliever use by a median of approximately nine puffs/day, compared with a change in only one-half of a puff per day among those using a competing breathing approach.50 While this finding would be strengthened if the investigators had also demonstrated improvement in asthma symptoms, this trial did not report changes in asthma symptoms in any peer-reviewed publications. Internet-based material identified through our grey literature search, however, qualitatively suggest symptoms improvement in this trial.109–111 We have concerns that these data may not be treated as rigorously in internet-based reports as they would be in a peer-reviewed journal, where methods are carefully assessed and statistical significance is generally presented. Regardless of whether these studies found an improvement in daily symptoms, participants were able to dramatically reduce reliever medication use without increasing the risk of a severe exacerbation.50 One other high-intensity trial reported both symptom medication outcomes and found reductions in both symptoms and reliever medication use.56 The three trials of the lower-intensity interventions all reported these outcomes and found no consistent group differences for either asthma symptoms or reliever medication use.57,59,71
Practitioners that trained patients in hyperventilation-reduction techniques generally coached patients to delay using reliever medication until they tried breathing methods and these techniques failed. Thus, reductions in reliever medication use may reflect intervention compliance or reduction in unnecessary use and may not be the result of improved pathophysiology. Despite uncertainty about causal factors or about coherence of medication and symptom-based outcomes, however, a reduction of 1.5 to 2.5 puffs of reliever medication per day, maintained for up to 6 months, would likely be viewed as clinically significant by most asthma patients. A reduction of nine puffs per day of reliever medication would be considered a large improvement by any standards, although our understanding of the true clinical significance is limited by the fact that they only reported short-term (3-month) outcomes.
Changes in controller medication use and asthma-related quality of life were rarely seen in the hyperventilation reduction trials, and none of these trials consistently reported improvement in pulmonary function, compared with usual care, attention control, or another breathing technique.
The BTS recommends that Buteyko breathing techniques be considered to help patients control asthma symptoms, which would be consistent with our findings.22 This recommendation was based on three of the trials included in our review,50,52,57 along with one additional trial that we excluded because it used a relaxation training comparison group.112 We included seven additional published trials and one unpublished trial, all of which were rated as fair quality, adding 1,145 additional participants. These include trials using hyperventilation reduction techniques that are not specifically limited to Buteyko methods, while the BTS guideline evidence base only included trials of Buteyko breathing training. The additional trials in our review had mixed findings, but generally supported the possible effectiveness of hyperventilation reduction techniques when compared with usual care, but not when compared with two other breathing techniques.
Yoga Breathing Techniques
The breathing techniques used in yoga are different from hyperventilation reduction methods. The techniques studied in the trials of yoga breathing involved deep breathing, sometimes with mechanically narrowed air passages and prolonged exhalation. In contrast, hyperventilation reduction breathing techniques advocate quiet, shallow breathing with breathing-holding. Both yoga and hyperventilation reduction methods, however, advocate the use nasal breathing rather than mouth breathing, and both appear to have the effect of slowing the passage of air in and out of the lungs. It is unclear if the two approaches have similar physiologic effects, so we elected to analyze these interventions separately.
We identified five trials examining yoga breathing techniques. Three very intensive trials were conducted in India, one of which also included dietary advice, cleansing techniques, and meditation. All three reported improvements in asthma symptoms, reductions in medication use, and improved pulmonary function.60,63,64 These trials had limited applicability to the U.S. health care system due to cultural differences and populations targeted. All three of these were small studies, one of which included only 8-week outcomes64 and two trials that included substantial methodological flaws.60,63 Since pulmonary function tests require maximal effort from the patient to get accurate results, and since technician behavior may affect the likelihood of maximal effort, high-quality training and monitoring of these tests are critical to protect against bias and type I error. Only one of the three studies reporting beneficial effects described pulmonary function test procedures in sufficient detail to provide assurance that test results were reliable.64
Of the two trials conducted in the United States,61,62 one included substantial components in addition to breathing techniques, which makes it impossible to determine the role of yoga breathing methods in the improvements in asthma outcomes.61 The other trial with good applicability to the United States reported on the efficacy of an eight-session yoga class and showed no differences between those randomized to yoga class compared with those randomized to a stretching class of the same intensity.62 Based on these findings, yoga does not appear to improve asthma as one might be typically introduced to yoga in the United States.
One trial designed to isolate the effects of yoga breathing exercises (as opposed to a comprehensive yoga program) showed reductions in asthma symptoms and improvement in pulmonary function, but this study had substantial methodological limitations and very limited applicability to the United States as it was conducted in people with at least 6 months of experience with yoga who were not using medications.63 Two additional trials focused exclusively on using a device to enhance prolonged exhalation, which is consistent with yoga breathing.52,70 Neither of these trials showed that this breathing approach without any other components improves asthma symptoms, reduces medication use, or improves pulmonary function. This suggests that a broader yoga program is needed to produce a benefit for asthma. How comprehensive of a program is needed to produce an effect, however, remains an open question.
A recent review studies employing yoga for asthma found evidence to be inconclusive among seven included trials. They reported mixed results in trials that were plagued by methodological limitations. We included only two of the trials from their review.62,64 The remaining trials were excluded because they did not meet our minimum quality criteria,95,113 were not published in English,33 used a form of yoga did not appear to include breathing exercises,114 or were published prior to 1990.115 The three additional trials that we included were two of the intensive India-based trials60,63 and one comprehensive program conducted in the United States,61 all of which did show benefits of treatment.
Some yoga practitioners have emphasized the need for individualized treatment, and that there can be no “asthma” treatment that could be broadly applied.116 Further, isolating elements such as breathing exercises only may be discouraged by many practitioners. Most of the trials in this review did have a specific protocol of breathing exercise and postures used by all participants, often performed in a group setting. Thus, these trials may underestimate the effect that might be possible if practitioners were able to individualize the treatment.
Inspiratory Muscle Training and Other Nonhyperventilation Reduction Breathing Techniques
This body of evidence does not allow us to draw conclusions about the effectiveness of IMT or nonhyperventilation reduction breathing techniques (three small heterogeneous trials). We only identified five IMT trials,65–69 three of which were conducted by the same researcher,67–69 and all but one67 had substantial methodological limitations. The best evidence comes from a small trial of 30 Israeli adults with moderate to severe asthma, who averaged six puffs of asthma medication per day at baseline.67 IMT participants showed greater improvements than those using a sham device, but no differences were seen in the two very similar trials in participants with lower baseline reliever medication use.68,69 A separate trial by the same author did show that improvements in inspiratory muscle strength, as measure by maximal inspiratory mouth pressure, were correlated with reductions in SABA use, among those undergoing IMT. This trial was not included in this review because it did not report group-specific outcomes.117
While the remaining IMT trials showed large group differences for some outcomes, but these were relatively small trials with substantial methodological limitations and low applicability to the United States.65,66 Our conclusions are consistent with a Cochrane review that concluded evidence was insufficient to determine whether IMT provides clinical benefit to asthma patients.118
Specific Versus Nonspecific Effects of the Breathing Techniques
Asthma control may be affected by numerous factors including, psychological (e.g., stress, anxiety, suggestion),30 physiological (e.g., respiratory infections, exercise), and environmental factors (e.g., allergens, weather). While training in hyperventilation reduction techniques may help improve asthma symptoms and reduce asthma reliever medication use, it is difficult to determine whether improvements could be attributed to the use of the specific techniques espoused for these interventions. Instructing patients to delay the use of reliever medication may be sufficient to reduce reliever medication use, since symptoms may sometimes resolve spontaneously. Thus, rather than directly improving asthma, trials might help participants eliminate unnecessary use of reliever medications, which is still an important positive outcome. Subjective assessment of asthma symptoms is responsive to placebo interventions (e.g., sham acupuncture or a placebo inhaler),119 and this may be sufficient to improve asthma symptoms in some cases, in addition to the enthusiastic advocacy by a treatment professional and dramatic testimonials. Some trials attempted to control the enthusiastic advocacy of the treatment modality by including comparison groups that involved other, plausible breathing retraining. However, it is difficult to say whether the treatment providers were comparable in their conviction that the techniques would be successful.
Another possibility is that these techniques improved asthma through reduction in anxiety or autonomic arousal. Asthma patients are more likely to have co-morbid anxiety disorders than those in the general population. They are also more likely to show greater bronchoconstriction in response to stress than health controls.30 Case-series in patients with co-morbid asthma and panic disorder suggest that asthma education plus psychological panic control approaches can reduce asthma symptoms.120 Participants in the two trials of hyperventilation reduction techniques in this review that measured anxiety did show greater reductions in anxiety scores than control participants.55,59 However, the clinical significance of these results was questionable because reductions in anxiety were small, participants averaged in the normal range of anxiety at both baseline and followup, and these studies were mixed with regard to asthma outcomes.55,59 Thus, it seems unlikely that reductions in anxiety in reported in these trials had a substantial impact on the reported asthma outcomes.
Regarding autonomic arousal, a Cochrane review of psychological interventions for adults with asthma included nine trials examining some form of relaxation training, including the trial of biofeedback included in this review.70 This review’s overall conclusion was that there was insufficient evidence to determine whether psychological therapies improve asthma. A closer look at the subset of trials reporting relaxation training, however, showed reductions in asthma medication use without improvements in asthma symptoms or pulmonary function in a number of trials. Thus, another possibility is that the reductions in reliever medication use that was found in our included trials may be related to reductions in level of autonomic arousal or anxiety, which may also be achieved through the use of relaxation techniques. Another trial (not included in the current review because the intervention was not a breathing retraining technique) using a “Senobi” stretch, which was designed to lower the level of autonomic arousal, similarly found a greater reduction in reliever medication use in participants doing the Senobi stretch three times daily (reduction from baseline of 1.7 uses per week), compared with those doing a forward bend three times daily (reduction of 0.4 uses per week).121 Many of the hyperventilation reduction trials in this review, however, reported reductions in asthma symptoms as well as medication use, at least among those offering more intensive interventions (5 hours or more of direct instruction). In contrast, the relaxation trials generally only reported improvements in medication use. A small trial (n=34) comparing Buteyko training with relaxation training offers further evidence that hyperventilation reduction methods may provide effects beyond reductions in autonomic arousal. This trial found that while both groups had symptom improvement, these improvement was greater in the Buteyko group.112 Although this is only a single, small trial, it suggests that Buteyko may have a greater effect than reduced autonomic arousal alone.
While there is some evidence that suggests that the specific effects of hyperventilation reduction techniques may outstrip the non-specific effects of the interventions, alternate hypotheses cannot be definitively ruled out. In particular, the effects of recommending delaying reliever medication use for 5 to 10 minutes while using methods that may reduce anxiety or arousal, bias in outcomes reporting, and the placebo effect. The last is the most troublesome because sources of information widely available via the internet present dramatic claims with great conviction, making the placebo effect difficult to minimize.
It can be very difficult to isolate critical treatment elements in complex interventions, and use of some elements in isolation may underestimate their importance if the components are dependent on each other or interact with each other, or if individuals vary in the degree to which specific components are necessary or sufficient to gain improvements. Thus, critical intervention components often cannot be elucidated, especially in this relatively flawed and heterogeneous body of research.
Strength of Evidence
The strength of the evidence for each outcome is presented by intervention group in Table 15. In most cases, the strength of evidence was insufficient or low. The evidence that hyperventilation reduction breathing techniques can reduce asthma symptoms and reliever medication use was judged to be moderate, as was evidence that hyperventilation reduction techniques are unlikely to improve pulmonary function.
Applicability of the Evidence to U.S. Health Care System
The included trials’ applicability to the U.S. setting and health care system was generally low, with trial-specific limitations listed in Tables 4 through 8. Only three of the trials were conducted in the United States.61,62,70 The hyperventilation reduction trials were primarily conducted in the United Kingdom and Australia, yoga trials were primarily conducted in India, and IMT trials were conducted in Israel, Brazil, and South Africa. Many of these countries have substantial cultural or economic differences from the United States, and the standard of usual asthma care may differ, as well as availability of practitioners. While having trials conducted in a number of different countries can improve cross-cultural applicability, in this case there are too many competing sources of heterogeneity to be able to identify which components may be transferable across cultures.
Some yoga and IMT trials were even further limited in their applicability to the general U.S. population by limiting samples to males60 or females only,68 vegetarians within a fairly narrow age range,60 people with 6 months of yoga experience and not using medications,63 and children with untreated asthma.65 Further, the standard of usual care in some of these trials also appeared to be different from the current U.S. standard of care due to nonuse of controller medications60,63 or poor success in managing asthma, further limiting our confidence in reported between-group differences.65
The hyperventilation reduction trials were primarily conducted in the United Kingdom51,52,55,56,71 and Australia,50,57,58 with the addition of one trial conducted in Canada53 and one trial conducted in Greece.54 As few studies reported outcomes beyond 6 months, results can only be generalized to short-term outcomes. One trial was limited to participants with dysfunctional breathing,71 which limits applicability to persons with asthma in general. This was a pertinent subgroup to the intervention offered, however, which provided physical therapy to reduce dysfunctional breathing.
While the included trials were generally conducted in health care settings, these countries have very different health care systems from the United States. Despite the differences in health care systems, however, the BTS guidelines22 and the NAEPP guidelines1 both have similar goals for asthma patients in that they advocate the use of controller medications to minimize the use of reliever medication for people with persistent asthma, so asthma treatment is likely fairly similar in the United Kingdom and the United States. Patients with poorly controlled asthma who are motivated to use complementary and alternative methods to minimize their use of medication and avoid overuse of reliever medications may be good candidates to try these techniques, if they can find a practitioner with the requisite expertise.
Finding a qualified provider, however, may not be a straightforward process. The Buteyko breathing technique is the most widely known of the hyperventilation reduction approaches, and is the only one specifically endorsed by the BTS.22 Additionally, several of the trials of hyperventilation reduction used certified Buteyko practitioners. Websites listing Buteyko practitioners indicate that there were only approximately 50 certified Buteyko practitioners in the United States, practicing in 21 states as of December 2011, and most worked in complementary and alternative medical settings.122–124
While many Buteyko providers emphasize the importance of proper training in practitioners, there appears to be some disagreement among practitioners about what constitutes necessary and sufficient training. For example, one group claims to be the only certifying group with the rights to teach the patented Buteyko method outside of Russia and included a warning that practitioners who were not on their list may not be qualified.122 Indeed, Konstantin Buteyko himself apparently did not approve all training and certifying organizations, and his supporters denounced two of the included trials50,53 as not using his techniques correctly, despite their report of using trained Buteyko practitioners.125 The single trial that used interventionists trained by Konstantin Buteyko himself did show the largest effects on medication use and was one of only two trials55,56 reporting a large effect on asthma symptoms.56 Regardless of Konstantin Buteyko’s opinions, while trials that used certified Buteyko practitioners were more likely to show reductions in medication use, they were also slightly less likely to show improvements in quality of life, compared with hyperventilation reduction trials that did not use certified Buteyko practitioners. Thus, while Buteyko-affiliated organizations strongly advocate for the importance of certification, the evidence does not unequivocally support this.
The evidence supporting yoga breathing techniques is not as strong as that for hyperventilation reduction techniques, and applicability of the evidence is also lower. Thus, there is no evidence to suggest that a typical person in the United States who does not have a strong interest in yoga would be likely to benefit from a yoga-based intervention. However, patients with asthma who are students of yoga and willing to undertake intensive training may find benefits of asthma-targeted practice with a trained yoga practitioner. Evidence for IMT or other breathing retraining approaches is too scant and low in applicability to suggest that asthma patients in the United States would likely find them beneficial.
Limitations
Potential Limitations of Our Approach
A potential limitation of our review is that we limited included studies to English language publications. Previous research has suggested that evidence for complementary and alternative treatments may be biased if non-English publications are excluded.126 We did examine the abstracts of any non-English publications identified in our searches that may have met inclusion criteria for our review, based on titles. We found only two trials that appeared that they could possibly meet inclusion criteria.33,34 One of the trials (published in German) compared breathing exercises, yoga, and usual care in 28 participants, finding that breathing exercises improved lung function (FEV1 and VC), while yoga and usual care did not. Effects on asthma symptoms, medication use, or quality of life were not reported in the abstract, nor in the tables or figures in the full text article.33 The other study (published in French) examined the effects of physical respiratory rehabilitation and physical training in the form on swimming on lung function, compared with a control group described as “immunotherapy alone.” The authors reported greater reduction in bronchial obstruction in children in the active treatment group, but did not report effects on asthma symptoms, medication use, or quality of life.34
Some proponents of Buteyko breathing techniques suggested that relevant early studies conducted by Buteyko himself may be only published in Russian. However, we did not find any Russian-language studies with descriptions or titles indicating that they were likely controlled trials conducted by Buteyko on websites devoted to his research. We feel it is very unlikely that the results of this review would be different if we had included trials published in other languages.
Another potential criticism is our exclusion of trials rating as having “poor” methodological quality. While some reviewers may believe that it is important to present all trials of any quality, we felt that if study results did not meet some minimal standard of internal validity then those results could be misleading and should not be presented. We found nine trials that were not included because they did not meet our minimal standards for quality or reporting (Appendix D).92–95,113,127–130 These trials assessed the effects of hyperventilation reduction breathing techniques,92–94 nonhyperventilation reduction breathing techniques,127–130 and yoga.95,113 One of these trials was a mere mention of a trial of biofeedback involving asthma patients with no actual data.93 Only three of the trials compared treatment groups statistically92,95,128 and one of these reported group differences.92 Threats to validity in these three trials included lack of baseline comparability, differential dropout between groups, very small numbers of participants, and lack of important information such as assessment methods and dropout. These trials were consistent with the included body of literature in that most trials reported a benefit of some kind on at least one outcome, though a variety of outcomes were reported and preferential reporting of statistically significant outcomes was possible.
We were unable to locate seven articles that may have met inclusion criteria (Appendix D).131–137 We believe it is likely that most if not all would not have met inclusion criteria for several reasons. None of these trials were included in other reviews of breathing retraining, despite the fact that most of them fell in the search window of at least one other review on this topic. Two were conference abstracts published by authors of trials that were included in this review, so conference abstracts could represent early reports on trials that were already included.134,135 Another study listed “Anonymous” as the author, so was likely a synopsis of another trial rather than original research.132 We believe the fact that we found these studies at all is testimony to the thoroughness of our grey literature searching.
We excluded trials that used relaxation training as a comparison group, since the efficacy of relaxation training for asthma is plausible but not established,138 so interpretation may have been difficult, particularly in the case of no differences between groups. A number of included trials had comparators that could plausibly induce a state of relaxation, such as meditation, stretching, and landscape videos with instruction to use “relaxed breathing.” We decided to err on the side of inclusion, which may have biased our review on the side of reduced effect sizes. Others may have chosen to exclude these trials. Also, we included trials that included a relaxation component along with the breathing training intervention, and possibly as a result we could not clarify the role of relaxation or reduced autonomic arousal vs. the role of the breathing training specifically in improving asthma outcomes.
When we had insufficient information to fully evaluate a trial, but had enough information to determine that it would likely meet inclusion criteria, we contacted authors and asked for the specific information we needed in order to complete our inclusion/exclusion determination and quality rating. Thus, we included information received through personal communication with authors, including extensive data received on the large Buteyko trial, which had only been published as a conference abstract at the time of this review.56 These data did not appear in peer-reviewed publications and are not widely available for verification. However, we felt that it was important to attempt to include all pertinent literature, both published and unpublished, to minimize publication bias and provide the most complete picture of the evidence possible. Quality standards were consistently applied to published and unpublished data. We did not contact authors who provided sufficient data to assign a quality rating and determine pertinent results, even if some data were missing, so these trials might have been at a slight disadvantage when assigned quality ratings. When we contacted authors, we asked only about information necessary to complete our quality rating or clarify data that were unclear to us.
Limitations of the Literature
Clinical and methodological heterogeneity was substantial across the entire body of literature, but in some cases a majority of the trials examining the same treatment approach were similar enough to consider combining them statistically. Due to heterogeneity of outcomes reported and lack of important outcomes in many trials, however, we were only able to perform meta-analyses for selected (not all) intervention approaches and for a limited number of outcomes. Even when comparable outcomes were reported, some trials were left out of the meta-analysis due to lack of necessary data (usually measures of variability such as standard deviations or confidence intervals). In the end, we were able to combine trials of only two interventions (hyperventilation reduction and yoga breathing training) for only three outcomes: asthma symptoms (hyperventilation reduction approaches vs. control only), quality of life (yoga vs. control only), and pulmonary function testing (for hyperventilation reduction and yoga trials). All pooled data are based on just three to five trials, so pooled results have a high probability of being more the 10 percent off from the true effect estimate.108
Finally, there was minimal comparative effectiveness research. Most trials compared a breathing retraining approach with some kind of control group. This was appropriate, given that effectiveness has not been well established for any treatment approaches. Nevertheless, once effectiveness is better established, the ability to compare approaches with each other on effectiveness and acceptability to asthma patients will be useful.
Clinical Implications
NAEPP guidelines advocate a stepwise approach to asthma management, with the goal “to maintain control of asthma with the least amount of medication and hence minimal risk for adverse effects.”1 One of the specific goals of the approach is to have people with asthma require a reliever medications no more than twice per week. Participants in the hyperventilation reduction trials were on average using relievers more frequently than twice per week at the beginning of the trial, generally averaging about two puffs per day or more. While there are flaws in the research, participants were generally successful in reducing reliever medication to a level consistent with NAEPP guidelines, at least in the short term, in most trials that provided a comprehensive approach to hyperventilation reduction breathing retraining, particularly those involving at least five hours of direct instruction. This was achieved without increases in asthma symptoms, exacerbations, or declines in lung function. For people whose asthma is not well-controlled, hyperventilation reduction techniques may provide a low-risk approach to achieve better control and avoid overuse of reliever medications. Participants in the trials were told only to reduce the use of controller medications after consulting their medical providers, and this is a very important safety consideration for all users of these techniques. Inflammation may increase with reduction in controlled medications without the patient realizing it, and lead to exacerbations in the longer term. Hyperventilation reduction techniques may be a useful tool in the larger asthma management toolbox, which also includes medication and other components as needed, such as environmental controls, symptom monitoring, and a plan for handling exacerbations.
While the available evidence base for yoga is not as strong in terms of quality and quantity, there is a small body of evidence suggesting that intensive yoga training may reduce asthma symptoms and improve lung function. Patients who would like to undertake intensive asthma-focused training need not be discouraged, but again should not change their use of asthma medication without consulting with their medical provider.
Evidence Gaps
Evidence gaps for all treatment approaches were substantial. For hyperventilation reduction techniques, there was only a single large trial, and it had not yet been published in a peer-reviewed journal.56 A fully published account of another large trial of at least fair-quality is crucial to confirm the effects seen in this review. None of the trials were conducted in the United States, which would be important if it is to be considered for wide-spread adoption here. Once replication has established its effectiveness more firmly, examination of components of care can be undertaken. We found little evidence that was clearly and directly applicable to non-Caucasian adults.
No large-scale trial of yoga training was found, and little evidence was found that was applicable to the United States.
No trials of IMT have been conducted in the United States, and all trials we found were small, including no more than 25 participants per treatment arm, and most had serious methodologic limitations. Only one investigator in this area has undertaken a systematic program of research to examine effects in different populations, and this work is still in the early stages.
The literature for other nonhyperventilation reduction breathing techniques is in its infancy, and a strong theoretical basis is needed to support further research in these and the other techniques examined.
Future Research
In general, there was little consistency of asthma-related terms used in these trials, and terms were sometimes used vaguely or differently, making it difficult to characterize interventions.
Bruton and colleagues suggest components that should be described when characterizing breathing retraining, and we strongly support their recommendations to improve our understanding of the interventions and to provide a framework for exploring differential effects of different components of breathing training.139 They suggest including information on route (nasal or oral), rate (breaths per minute), depth (e.g., shallow, normal.), inspiratory and expiratory flow speed, region (e.g., abdominal), timing, regularity (of volume, timing, rate), breath holds, repetitions, and whether manual assistance was involved. Careful and consistent descriptions of specific techniques used would allow exploration of effectiveness of specific elements.
All intervention types would benefit from additional studies and evidence. In addition to detailing breathing retraining techniques as described by Bruton and colleagues, future studies should include outcomes of asthma symptoms, reliever medication use, quality of life, and pulmonary function at minimum.139 In addition, controller medication use should always be described. Best practices regarding randomization, blinding, and followup are also crucial to any further research in this area. Trials should include asthma treatment with medications and education that is consistent with the standard of care in the United States.
Because asthma control fluctuates and many factors can affect asthma control (psychological, environmental, physiological), it is important to have large enough samples to capture appropriately diverse groups or asthmatics, with long enough followup to ensure that changes are stable. Outcome measurements should be repeated over time with follow-up through at least 6 months, and preferably through12 months, to capture ensure effects remain through all seasons.
Further examination of the impact of targeting autonomic arousal in controlling asthma may be helpful. Trials should compare a relaxation-only arm with relaxation plus a breathing technique to determine if the breathing technique adds to the benefit of relaxation alone.
Given that the current state of the evidence differed across intervention approaches, specific suggested next steps by intervention approach include:
- Hyperventilation reduction breathing techniques:
- Replication of results of the large, good-quality trial with intensity-matched comparator and valid, blinded outcome assessment
- In addition to matching treatment intensity between treatment and control groups, researchers should also attempt to match the groups in terms of what kind of change in asthma the patient is told they can expect. The internet is replete with dramatic testimonials as to the effectiveness of Buteyko breathing methods, and researchers should attempt to provide comparable levels of confidence in their techniques for treatment and control groups
- Test the effects of delaying reliever medication use for 5 to 10 minutes while using techniques designed to reduce anxiety and autonomic arousal, compared with delay of reliever use for 5 to 10 minutes while using hyperventilation reduction techniques in order to examine the effects of reliever medication delay separate from breathing techniques.
- Trials focused on hyperventilation reduction techniques in children and older adults
- Trials that include substantial numbers of non-Caucasian participants
- Trials that attempt to isolate the necessity or efficacy of other specific components of treatment
- Yoga breathing techniques
- Well-designed and executed replication of a high-intensity approach in the United States, without additional non-yoga components
- IMT
- Well-designed and executed trial comparing a training device with a sham device, with larger n, in the United States, such as that used in the Weiner study67
- Summary and Discussion - Breathing Exercises and/or Retraining Techniques in the...Summary and Discussion - Breathing Exercises and/or Retraining Techniques in the Treatment of Asthma: Comparative Effectiveness
- Results - Breathing Exercises and/or Retraining Techniques in the Treatment of A...Results - Breathing Exercises and/or Retraining Techniques in the Treatment of Asthma: Comparative Effectiveness
- Methods - Diagnosis and Treatment of Obstructive Sleep Apnea in AdultsMethods - Diagnosis and Treatment of Obstructive Sleep Apnea in Adults
- Peer Reviewers - Breast Reconstruction After Mastectomy: A Systematic Review and...Peer Reviewers - Breast Reconstruction After Mastectomy: A Systematic Review and Meta-Analysis
- Acknowledgments - Adverse Effects of Pharmacologic Treatments of Major Depressio...Acknowledgments - Adverse Effects of Pharmacologic Treatments of Major Depression in Older Adults
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