This review should be cited as: Linde K, Jobst K, Panton J. Acupuncture for chronic asthma (Cochrane Review). In: The Cochrane Library, Issue 2, 2001. Oxford: Update Software.
A substantive amendment to this systematic review was last made on 21 October 1998. Cochrane reviews are regularly checked and updated if necessary.
Background: Acupuncture has traditionally been used to treat asthma in China and is used increasingly for this purpose internationally.
Objectives: The objective of this review was to assess the effects of acupuncture for the treatment of asthma or asthma-like symptoms.
Search strategy: We searched the Cochrane Airways Group trials register, the Cochrane Complementary Medicine Field trials register and reference lists of articles.
Selection criteria: Randomised and possibly randomised trials using acupuncture to treat asthma and asthma-like symptoms. Acupuncture could involve the insertion of needles or other forms of stimulation of acupuncture points.
Data collection and analysis: Trial quality was assessed by at least two reviewers independently. A reviewer experienced in acupuncture assessed the adequacy of the sham acupuncture. Study authors were contacted for missing information.
Main results: Seven trials involving 174 people were included. Trial quality varied and results were inconsistent.
No statistically significant or clinically relevant effects were found for acupuncture compared to sham acupuncture. However the points used in the sham arm of some studies are used for the treatment of asthma according to traditional Chinese medicine. Only one study used individualised treatment strategies.Lung function could be compared statistically in only 3 trials. Peak expiratory flow rate showed a statistically insignificant increase of 8.4 litres/minute weighted mean difference (95% confidence interval -29.4 to 46.2) when acupuncture was compared to sham acupuncture.
Reviewers' conclusions: There is not enough evidence to make recommendations about the value of acupuncture in asthma treatment. Further research needs to consider the complexities and different types of acupuncture.
Background
Bronchial asthma is a major health problem and has a significant mortality. Data on the prevalence of asthma vary between 3 and 6% for adults and between 8 and 12% in children and suggest an increasing incidence within recent years . Although the symptoms can be controlled by drug treatment in most patients, effective low-risk, non-drug strategies could constitute a significant advance in asthma management.
Acupuncture has traditionally been used in asthma treatment in China and is increasingly applied in Western countries. In 1991 Kleijnen et al. (Kleijnen 1991) published a systematic review of the controlled clinical trials in asthma. They concluded that claims for the effectiveness of acupuncture in the treatment of asthma are not based on the results of well performed clinical trials. Unfortunately, this review was limited mainly to an assessment of methodological quality and gave little information on what was investigated in the primary studies. Results of primary studies were categorized only as positive or negative (vote count), a method which may have low validity.
Two further overviews have been published recently (Jobst 1995, Linde 1996). These reviews form the basis for this Cochrane review.
See: Collaborative Review Group search strategy
The Asthma and Wheez* database of the Cochrane Airways Group was searched for all trials including the word "acupuncture" or "acupressure" (last update summer 1998). The search strategy is described in the Cochrane Library (section Airways Collaborative Review Group).Methods of the review
Selection of trials:
From a large number of papers on acupuncture and asthma screened we identified 21 controlled clinical trials. At least two of the three reviewers independently assessed eligibility and selected seven of these 21. The main reasons for exclusion were short observation periods (i.e., studies on induced / spontaneous asthma attacks) and non-random allocation (see reasons for exclusions in the table of excluded studies). Trials with short observation periods do not seem relevant for the primary objective of this review as acupuncture is primarily used as an adjuvant therapy in the long-term treatment of asthma. These trials have been summarized in the reviews by Jobst (Jobst 1995) and Linde et al. (Linde 1996).
Initial disagreements occurred for two papers but could be resolved by discussion.
Data extraction and quality assessment:
Descriptive characteristics and study results were extracted using a standard form. Concealment of randomisation, blinding of patients and evaluators, and likelihood of selection bias after randomisation were assessed by at least two reviewers and disagreements were resolved by discussion. In addition one reviewer assessed quality of reporting using the score by Jadad et al. (Jadad 1996). One of the reviewers who is experienced in acupuncture assessed the adequacy of sham-acupuncture.
Letters asking for additional information were sent to all first authors in August 1996. Only two responded and only one could provide additional information.
Where appropriate, data were entered as negative values to conform to the Cochrane convention whereby effects that favour the treatment under review move to the left.
Patient Characteristics:
Asthma was defined as reversible airways obstruction. Criteria varied between trials and two did not make their criteria explicit.
Samples were comprised of patients of varying characteristics. One trial included children only, five trials selected adults only, and one trial children and adults. Although it was not clear in all cases, we have assumed that all subjects were outpatients drawn from a variety of hospital settings.
One trial included patients diagnosed as suffering from COPD, with some having documented reversible airways disease (Jobst 1986).
Intervention Characteristics - Experimental Group:
The acupuncture strategies used differed considerably between trials.
In five trials needles were inserted, while in two trials stimulation was carried out using lasers. Six trials used formula acupuncture (identical points for all patients), but formulas differed strongly between trials. In one trial individualised acupuncture points were used according to the theory of traditional Chinese medicine.
Intervention Characteristics - Control Group:
All trials involved some form of 'dummy' acupuncture. In three trials true acupuncture points thought to be ineffective for asthma were stimulated. However according to Chinese medicine, some of these points might have some treatment effect, so they might not be considered to be fully inert placebo strategies. In other trials stimulation was done in areas where no acupuncture points are known. No trial included a no treatment control or compared acupuncture with another treatment.
Presentation of results:
In most trials results were not presented in a way suitable for meta-analysis. For example, instead of means and standard deviations, medians and ranges were presented. Authors were contacted; two replied, but only one could provide additional relevant information.
Therefore, only a small proportion of the trials contributed to the overall meta-analysis.
Lung Function:
All studies measured lung function at varying points in time. Apart from the fundamental problem of the incomparability of the trials, data were presented so inconsistently that it was impossible to pool the results. 3 studies presented peak expiratory flow rates (PEFR - a measure of lung function) after the end of the acupuncture treatment phase.
No statistically significant or clinically relevant effect was found for acupuncture (average difference between real and sham acupuncture 8.4 l/min; 95% confidence interval -29.4 to 46.2 l/min). The results of the other 4 trials showed no marked effect over sham.
Drug use:
Six of the seven studies attempted to monitor drug use. However, actual data were presented in only four studies and monitoring and assessment methods differed fundamentally, precluding meta-analysis. Only one trial (Christensen 1984) found a statistically significant decrease of medication use over placebo after 2 weeks of treatment.
Subjective Measurements:
All trials attempted to monitor subjective symptoms in some way. Again, differing methods and data presentation precluded a meaningful meta-analysis. Two trials (Christensen 1984; Jobst 1986) reported significant improvements over placebo.
Other results:
One trial (Jobst 1986) reported a significant increase over placebo in the six-minute walking distance.
Discussion
Seven randomised clinical trials with a total of 174 patients, comparing acupuncture with some form of dummy acupuncture in addition to standard maintenance medication, met the inclusion criteria of this review. No trials could be matched for sample, design, intervention or outcome measures and all used small sample sizes. In only 3 trials were there any data in which some comparison might be considered valid. This was the post-treatment PEFR, a measure of lung function, which showed a statistically and clinically non-significant increase of only 8 l/min, a figure which is clinically insignificant.
In a number of studies real acupuncture points were used as a placebo control condition. According to traditional Chinese acupuncture texts, some of these points can be indicated for the treatment of asthma. That means, in effect, that from the point of view of traditional Chinese medicine two treatments have been compared rather than a treatment and an inert control.
Particular care should be taken in selecting patients so that they may be matched for parameters such as age, duration of asthma and severity of lung function abnormalities.
Similarly, attention needs to be paid to the nature or style of acupuncture used (for a introduction to acupuncture see, for example, Stux 1997 or Helms 1998). The available evidence does not allow objective comparison between different acupuncture types. Therefore, it is not possible to comment on claims by proponents of any technique or style that any one is better than any other.
A major issue complicating the evaluation and integration of acupuncture in the western world is the model of treatment. If applied according to the principles of traditional Chinese medicine, acupuncture often comes as part of a package of care that includes diet and herbal medicines. The acupuncturist may modify the sites in different patients with asthma, as according to the traditional Chinese nosology these patients may have different disorders. From a western perspective such a treatment seems "individualized". Outside China, "standardized" treatment strategies are frequently used. These strategies are more compatible with western thinking. However, as a growing number of western acupuncturists also apply traditional Chinese strategies, a deliberate restriction to evaluating only the "standardized" model might not be adequate.
Few trials specifically evaluated the side-effect and morbidity profile of acupuncture treatments. Overall, the safety profile of acupuncture appears to be excellent and data have been reported in patients treated for asthma and breathlessness (Jobst 1995), but some have drawn attention to the complications which may follow acupuncture treatment. (See Jobst 1995, Jobst 1996, Ernst 1996, Norheim 1996)
This review highlights the fact that any trial or investigation of acupuncture is a complex challenge and that many different parameters need to be controlled for and investigated. For example, needle depth, type of needle manipulation (manual, electrical stimulation, moxibustion etc), siting of needles, induction of dachi (an irradiating sensation after needling thought to indicate effective needling), duration of insertion, duration of stimulation, use of standardised formulae versus individualised prescribing, to cite but a few. Researchers would therefore be well advised to consult widely and in particular to take advice from those who have knowledge of the different styles of acupuncture practice and of trial design and methodology.
References to studies included in this review
Christensen 1984 (published data only) * Christensen PA, Laursen LC, Taudorf E, St�rensen SC, Weeke B. Acupuncture and bronchial asthma. Allergy 1984;39:379-385. Christensen PA, Laursen LC, Taudorf E, St�rensen SC, Weeke B. Acupuncture for asthma patients. Ugeskrift for Laeger 1986;148:241-243. Dias 1982 (published data only) Dias PLR, Subramaniam S, Lionel NDW. Effects of acupuncture in bronchial asthma: Preliminary communication. J Roy Soc Med 1982;75:245-248. Hirsch 1994 (published data only) Hirsch D, Leupold W. Plazebo-kontrollierte Doppelblindstudie zur Wirkung der Laserakupunktur beim kindlichen Asthma bronchiale. Atemwegs-Lungenkr 1994;20:701-705. Jobst 1986 (published and unpublished data) Jobst K, Chen JH, McPherson K, et al. Controlled trial of acupuncture for disabling breathlessness. Lancet 1986;ii:1416-1418. Mitchell 1989 (published data only) Mitchell P, Wells JE. Acupuncture for chronic asthma: A controlled trial with six months follow-up. Am J Acupunct 1989;17:5-13. Tandon 1991 (published data only) Tandon MK, Soh PFT, Wood AT. Acupuncture for bronchial asthma? A double-blind crossover study. Med J of Aust 1991;154:409-412. Tashkin 1985 (published data only) Tashkin DP, Kroening RJ, Bresler DE, Simmons M, Coulson AH, Kerschner H. A controlled trial of real and simulated acupuncture in the management of chronic asthma. J Allergy Clin Immunol 1985;76:855-864. * indicates the major publication for the study References to studies excluded from this review Berger 1975 Berger D, Nolte D. Hat Akupunktur einen nachweisbaren bronchiospasmolytischen Effekt bei Asthma bronchiale. Med Klin 1975;70:1827-1830. Berger D, Nolte D. Acupuncture in bronchial asthma: bodyplethysmographic measurements of acute bronchospasmolytic effects. Comparative Medicine East & West 1977;5:265-269. Chow 1983 Chow OKW, So SY, Lam WK, Yu DYC, Yeung CY. Effect of acupuncture on exercise-induced asthma. Lung 1983;161:321-326. Fung 1986 Fung KP, Chow OKW, So SY. Attenuation of exercise-induced asthma by acupuncture. Lancet 1986;ii:1419-1422. Joos 1997 Joos S, Schott C, Zou H, Daniel V, Martin E. Akupunktur - immunologische Effekte bei der Behandlung des allergischen Asthma bronchiale. Allergologie 1997;20:63-68. Luu 1985 Luu M, Maillard D, Pradalier A, Boureau F. Contr�le spirom�trique dans la maladie asthmatique des effets de la puncture de points douloureux thoraciques. R�spiration 1985;48:340-345. Morton 1993 Morton AR, Fazio SM, Miller D. Efficacy of laser-acupuncture in the prevention of exercise-induced asthma. Ann Allergy 1993;70:295-298. Sovijarvi 1977 Sovijarvi AR, Poppius H. Acute bronchodilating effect of transcutaneous nerve stimulation in asthma. A peripheral reflex or psychogenic response. Scand J Resp Dis 1977;58:164-169. Takishima 1982 Takishima T, Mue S, Tamura G, Ishihara T, Watanabe K. The bronchodilating effect of acupuncture in patients with acute asthma. Ann Allergy 1982;48:44-49. Tandon 1989 Tandon MK, Soh PFT. Comparison of real and placebo acupuncture in histamine-induced asthma. A double-blind crossover study. Chest 1989;96:102-105. Tashkin 1977 Tashkin DP, Bresler DE, Kroening RJ, Kerschner H, Katz RL, Coulson A. Comparison of real and simulated acupuncture and isoproterenol in methacholine-induced asthma. Ann Allergy 1977;39:379-387. Virsik, 1980 Virsik P, Kristufek P, Bangha O, Urban S. The effect of acupuncture on pulmonary function in bronchial asthma. Prog Resp Res 1980;14:271-275. Yu 1976 Yu DYC, Lee SP. Effect of acupuncture on bronchial asthma. Clin Sci Mol Med 1976;51:503-509. Additional references Ernst 1996 Ernst E. Direct risks associated with complementary therapies. In: Ernst E, editor(s). Complementary medicine - an objective appraisal. Oxford: Butterworth-Heinemann, 1996:112-125. Helms 1998 Helms JM. An overview of medical acupuncture. Altern Ther Health Med 1998;4:35-45. Jadad 1996 Jadad AR, Moore RA, Carrol D, Jenkinson C, Reynolds DJM, Gavaghan DJ, McQuay HJ. Assessing the quality of reports of randomized clinical trials: is blinding necessary? Controlled Clin Trials 1996;17:1-12. Jobst 1995 Jobst KA. A critical analysis of acupuncture in pulmonary disease: efficacy and safety of the acupuncture needle. J Altern Complement Med 1995;1:57-84. Jobst 1996 Jobst KA. Acupuncture in asthma and pulmonary disease: an analysis of efficacy and safety. J Alternat Comp Med 1996;2(179-206). Kleijnen 1991 Kleijnen J, ter Riet G, Knipschild P. Acupuncture and asthma: a review of controlled trials. Thorax 1991;46:799-802. Linde 1996 Linde K, Worku F, St�r W, Wiesner-Zechmeister M, Pothmann R, Weinschtz T, Melchart D. Randomized clinical trials of acupuncture for asthma - a systematic review. Forsch Komplementarmed 1996;3:148-155. Norheim 1996 Norheim AJ, Fonnebo V. Acupuncture adverse effects are more than occasional case reports: results from questionnaires among 1135 randomly selected doctors, and 197 acupuncturists. Comp Ther Med 1996;4:8-13. Stux 1997 Stux G, Pomeranz B. Basics of acupuncture. 4 Edition. Berlin: Springer, 1997.Cover sheet
| Reviewer(s) | Linde K, Jobst K, Panton J |
| Contribution of Reviewer(s) | All authors participated in protocol development, extraction and analysis of the primary studies and writing of the manuscript |
| Issue protocol first published | 1996 Issue 3 |
| Issue review first published | Information not available |
| Date of most recent amendment | 12 February 2001 |
| Date of most recent substantive amendment | 21 October 1998 |
| Most recent changes | Information not supplied by reviewer |
| Date new studies sought but none found | Information not supplied by reviewer |
| Date new studies found but not yet included/excluded | Information not supplied by reviewer |
| Date new studies found and included/excluded | Information not supplied by reviewer |
| Date reviewers' conclusions section amended | Information not supplied by reviewer |
| Contact address | Dr Klaus Linde Researcher Centre for Complementary Medicine Research/Department of Gastroenterology Technical University Kaiserstr. 9 Munchen GERMANY 80801 Telephone: +49-89-33041048 Facsimile: +49-89-393484 E-mail: [email protected] |
| Cochrane Library number | CD000008 |
| Editorial group | Cochrane Airways Group |
| Editorial group code | HM-AIRWAYS |
Extramural sources of support to the review
Intramural sources of support to the review
List of comparisons
Fig 01 ACUPUNCTURE V SHAM ACUPUNCTURE
Tables of other data
Tables of other data are not available for this review
Additional tables
Additional tables are not available for this review
| Study | Methods | Participants | Interventions | Outcomes | Notes | Allocation concealment |
|---|---|---|---|---|---|---|
| Christensen 1984 | RCT (randomisation concealment unclear). Attempts were made to blind patients and evaluators. Duration 11 weeks (2 weeks baseline period). | N=18 (11 female, 7 male), age range 19-48. Outpatients from Danish hospital. Diagnosis - stable bronchial asthma, FEV1 < 70% predicted. At least 4 puffs daily of a beta2-agonist required. No previous steroids, cromoglycate or acupuncture. | Experimental Group (n=8): Standard formula (Co4 x 2, Ex 17 x 2, UB 13 x 2, CV 17) manual insertion with electrostimulation, variable needle depth and dachi. 10 sessions of 20 mins (twice weekly). Control Group (n=9): Sham acupuncture at non-acupuncture points. Uniform needle depth, no electrostimulation and no dachi. Acupuncturist quality: insufficient information. | Pulmonary function, subjective symptoms, drug use at -2, 0, 2, 5 and 9 weeks. IgE levels at 0, 5 and 9 weeks. | All results seem to favour acupuncture but due to the small sample size definite conclusions cannot be drawn. Results for data analysis were extrapolated from figures presenting the mean and standard error of the mean. Therefore extreme caution is required when interpreting the results. A significant proportion of results presented were unsuited to entry into Revman. | B |
| Dias 1982 | RCT (randomisation concealment unclear). Attempt to blind patients and evaluators. Varying observation periods for different patients (2-12 weeks) | N=20 (10 female, 10 male), age range 18-73. Outpatients of a general hospital in Sri Lanka. Diagnosis - chronic bronchial asthma. Poor response to Western drugs. All patients on 'some form of medication' (no clear in-/exclusion criteria given), duration of symptoms 1 to 41 years | Experimental group (n=10): Standard formula acupuncture (Ex17, Lu7, CV22), 2 to 12 treatment sessions (varying according to patients), duration of a session 30 minutes Control group (n=10): Sham acupuncture at acupuncture points (GB5,6) not indicated for asthma (see notes) Acupuncturist quality: Physician, Diploma in Peking. Both groups had breathing exercises | Pulmonary function, drug use, subjective assessment (before and after acupuncture treatment) | Results seem to favour sham acupuncture but due to small sample size and methodological flaws definite conclusion cannot be drawn. Problems: 1. variable observation period for individual patients 2. extremely heterogeneous population 3. GB5,6 used for sham control can be indicated in some asthma patients according to traditional Chinese medicine 4. Insufficient information on breathing exercises (type, compliance, education, length of practice etc) INSUFFICIENT REPORTING | B |
| Hirsch 1994 | R(?)CT (randomization not explicitly described but likely). Attempt to blind patients and evaluators. Crossover design (5 weeks each phase, no washout). | N=39 randomised (15 female, 24 male), age range 5-17 years, 32 analysed. Outpatients of an academic teaching hospital in Germany. Diagnosis - children with mild to moderately severe asthma, according to ATS (American Thorarcic Society) criteria. 28 used inhaled beta-agonist, 4 cromoglycate. Children taking oral or inhaled steroids excluded. | Experimental Group: Laser acupuncture, standard formula (Ex 1, Lu 1, 5 & 7, Co 4, UB 13 & 17, Ki 3, Sp 6, CV 17) - laterality not stated. 15 treatment sessions (thrice weekly), 20 seconds per point. Control Group Same points, laser switched off. Acupuncturist quality: Trained by a German syndicate; not traditional Chinese medicine. | Peak flow, subjective symptoms and drug use recorded daily by the patient. Spiromety and provocation test before and after each treatment phase. | Overall no significant differences between the groups. Insufficient data presentation. Assertions that significant improvement was seen in placebo group unsupported by data reported. | B |
| Jobst 1986 | RCT (adequate concealment of randomisation). Patients and evaluators blinded (blinding tested and successful). 2 weeks run in period, 3 weeks treatment and observation period. | N=26 randomised, age range 44-80, 24 analysed. Outpatients of a University Hospital in Britain. Diagnosis - Chronic obstructive pulmonary disease and reversible airways disease. | Experimental Group (n=13): Individualised traditional Chinese acupuncture and moxibustion - manual stimulation, variable needle insertion at site, depth and duration. 13 treatment within three weeks. Control Group (n=13): Sham acupuncture at acupuncture points (matched for number of insertions, duration and moxibustion). Conventional medication sustained. Some patients taking corticosteroids. Acupuncturist quality: Professor of Traditional Chinese Medicine and of orthodox respiratory medicine, Peking. | Pulmonary function, breathlessness, wellbeing, 6 minute walking and drug use. | Results indicate significantly greater benefit for real acupuncture in all subjective scores and 6 minutes walking distance. No significant changes in pulmonary function. Acupuncture points not given. | A |
| Mitchell 1989 | RCT (randomisation concealment unclear). Attempt to blind patients and evaluators. Duration of 42 weeks (4 weeks baseline). | N=31, 29 analysed (17 female, 12 male). Age range 15-43. Outpatients of a hospital in New Zealand. Diagnosis - chronic asthma; > 20% variation in PEFR on >7/14 days. No oral steroids, but low dose aerosol steroids. | Experimental Group (n=16): Standard formula acupuncture (CV 17, UB 13, Ex 17, Li 3) bilaterally, 8 treatment sessions for 15 minutes with manual stimulation once weekly. Control Group (n=15): Sham acupuncture at acupuncture points "not indicated for asthma". (Sp 8, Ki 9, GB 37) bilaterally. In both groups dachi achieved. Acupuncturist quality: Physician - training not stated. | Pulmonary function, drug use and subjective symptoms. | Insufficient data presented. No significant differences between groups reported. Both showed significant improvements in lung function and symptom scores and decline in medication use. Relevant loss to follow up. Sham points may have had an effect on asthma symptoms. | B |
| Tandon 1991 | RCT (randomisation concealment unclear). Attempt to blind patients and evaluators. Crossover design. 3 weeks baseline, 5 weeks treatment 1, 3 weeks washout, 5 weeks treatment 2. | N=15, (6 female, 9 male). Age range 19-57 years. Diagnosis - Chronic stable asthma according to American Thoracic Society (ATS) criteria. All on inhaled steroids, all except 1 on theophylline. No oral steroids or cromoglycate. | Experimental Group: Laser acupuncture standard formula (Sp 6 x 2, ST 36 x 2, Lu 9 x 2, Co 11 x 2, CV 17, CV 22, Ex 17 x 2, UB 13 x 2, ear:asthma/lung points). 10 treatment sessions twice weekly. Control Group: Sham points (Gb 34 x 2, Li 8 x 2, Li 14 x 2, Si 3 x 2, Si 6 x 2, UB 18 x 2, UB 25 x 2, ear:uterus and bladder points) Acupuncturist quality: Physician, training not stated. | Pulmonary function, drug use, symptom score and treatment preference. | Crossover design and data presentation unsuited for meta-analysis. No significant effects between or within groups. Sham placebo points can be used routinely in the treatment of asthma (according to Traditional Chinese Medicine). | B |
| Tashkin 1985 | RCT (randomisation concealment unclear). Attempts to blind patients and evaluators. Crossover trial. 4 weeks baseline, 4 weeks treatment 1, 3 weeks wash-out, 4 weeks treatment 2, 3 weeks follow-up | N=25 (15 female, 10 male) Age range 8 - 70. Diagnosis - Moderate to severe stable chronic asthma. FEV1 < 60% predicted. Most on oral and inhaled beta-agonists and theophylline. Most also on oral steroids. 11 on cromoglycate. | Experimental Group: Standard formula of acupuncture (Co 4, GV 14, Ex 17, St 36, Lu 7, Waitingchuan). 8 treatment sessions of 15 minutes twice weekly, manual stimulation. Control Group: Sham acupuncture at non-acupuncture points. Acupuncturist quality: Physician - training not stated. | Pulmonary function, subjective measurements, drug use, number of attacks. | Data presentation and crossover design unsuited for meta-analysis. No significant differences were found between or within groups. | B |
| Study | Reason for exclusion |
|---|---|
| Berger 1975 | Not randomised controlled trial. |
| Chow 1983 | RCT on induced asthma attacks (not covered by this review) |
| Fung 1986 | RCT on induced asthma attacks (not covered by this review) |
| Joos 1997 | Only measurement of immunological parameters |
| Luu 1985 | RCT of thoracic trigger points with evaluation of lung function 2hs after treatment |
| Morton 1993 | RCT on induced asthma attacks (not covered by this review) |
| Sovijarvi 1977 | Not randomized, short-term observation |
| Takishima 1982 | Not randomized, short term observation |
| Tandon 1989 | RCT on induced asthma (not covered by this review) |
| Tashkin 1977 | RCT on induced asthma attacks (not covered by this review) |
| Virsik, 1980 | Not randomized, short time observation |
| Yu 1976 | Randomization not reported, treatment on an acute attack |
Table of ongoing studies
A table of ongoing studies is not available for this review
