We wanted to find out if inspiratory muscle training (IMT) using an external resistive device is better than no treatment (or usual care) in people with chronic asthma. An external resistive device is something that makes it harder for the patient to breathe in. The idea is that doing breathing exercises with a device that makes it harder to breathe in helps to strengthen the muscles of respiration (for example like lifting a weight) and strengthens the muscles that pump air into the lungs. This would make it easier for the person to breathe during day-to-day life. This review aimed to explore the effect of IMT in asthma.
Asthma is the most common chronic disease found in children and young adults. Clinically, asthma is characterized by symptoms of shortness of breath, wheeze and cough, and episodes of worsening of symptoms. The objective of asthma treatment is to achieve and maintain control of the disease and to reduce symptoms. In most cases the symptoms can be controlled with inhalers, but IMT may assist treatment. For people with other chronic respiratory diseases, IMT significantly increases the strength of the inspiratory muscles, reduces dyspnoea and improves quality of life. It is unclear whether inspiratory muscle training has similar benefits in individuals with asthma.
We found and included five studies in our review. Three studies were conducted by the same group of researchers in Israel (Weiner 2000; Weiner 2002; Weiner 2002a), one study (Sampaio 2002) was conducted in Brazil and one trial was conduced in the United Kingdom (McConnell 1998). A total of 113 adults with asthma (46 male and 67 female) were included. No study included children.
The studies showed a significant improvement in inspiratory muscle strength (PImax). People with asthma who received IMT on average increased their inspiratory muscle strength, but it was not possible to state whether this improvement seen in inspiratory muscle strength translated into any clinical benefit. Results from one study showed no significant difference between the training group and the control group (no treatment or usual care) for expiratory muscle strength, lung function, sensation of dyspnoea (breathlessness) and use of reliever medication. There were no studies describing exacerbation events that required use of reliever medication or emergency department visits, inspiratory muscle endurance, hospital admissions and days off work or school. Given the insufficient evidence found in this review, we believe that there is a need for more well conducted studies in order to assess the efficacy of IMT in people with asthma, including children.
Quality of the evidence
There were substantial differences between the studies, including the training protocol, duration of training sessions (10 to 30 minutes) and duration of the intervention (over 3 to 25 weeks). The methodological quality of the studies included in this update was difficult to accurately ascertain. Study samples were small and the risk of bias was mostly unclear, due to inadequate reporting. Overall the quality of the evidence included in the review was very low. This summary was current to November 2012.
There is no conclusive evidence in this review to support or refute inspiratory muscle training for asthma. The evidence was limited by the small number of trials with few participants together with the risk of bias. More well conducted randomised controlled trials are needed. Future trials should investigate the following outcomes: lung function, exacerbation rate, asthma symptoms, hospital admissions, use of medications and days off work or school. Inspiratory muscle training should also be assessed in people with more severe asthma and conducted in children with asthma.
In some people with asthma, expiratory airflow limitation, premature closure of small airways, activity of inspiratory muscles at the end of expiration and reduced pulmonary compliance may lead to lung hyperinflation. With the increase in lung volume, chest wall geometry is modified, shortening the inspiratory muscles and leaving them at a sub-optimal position in their length-tension relationship. Thus, the capacity of these muscles to generate tension is reduced. An increase in cross-sectional area of the inspiratory muscles caused by hypertrophy could offset the functional weakening induced by hyperinflation. Previous studies have shown that inspiratory muscle training promotes diaphragm hypertrophy in healthy people and patients with chronic heart failure, and increases the proportion of type I fibres and the size of type II fibres of the external intercostal muscles in patients with chronic obstructive pulmonary disease. However, its effects on clinical outcomes in patients with asthma are unclear.
To evaluate the efficacy of inspiratory muscle training with either an external resistive device or threshold loading in people with asthma.
We searched the Cochrane Airways Group Specialised Register of trials, Cochrane Central Register of Controlled Trials (CENTRAL), ClinicalTrials.gov and reference lists of included studies. The latest search was performed in November 2012.
We included randomised controlled trials that involved the use of an external inspiratory muscle training device versus a control (sham or no inspiratory training device) in people with stable asthma.
We used standard methodological procedures expected by The Cochrane Collaboration.
We included five studies involving 113 adults. Participants in four studies had mild to moderate asthma and the fifth study included participants independent of their asthma severity. There were substantial differences between the studies, including the training protocol, duration of training sessions (10 to 30 minutes) and duration of the intervention (3 to 25 weeks). Three clinical trials were produced by the same research group. Risk of bias in the included studies was difficult to ascertain accurately due to poor reporting of methods.
The included studies showed a statistically significant increase in inspiratory muscle strength, measured by maximal inspiratory pressure (PImax) (mean difference (MD) 13.34 cmH2O, 95% CI 4.70 to 21.98, 4 studies, 84 participants, low quality evidence). Our other primary outcome, exacerbations requiring a course of oral or inhaled corticosteroids or emergency department visits, was not reported. For the secondary outcomes, results from one trial showed no statistically significant difference between the inspiratory muscle training group and the control group for maximal expiratory pressure, peak expiratory flow rate, forced expiratory volume in one second, forced vital capacity, sensation of dyspnoea and use of beta2-agonist. There were no studies describing inspiratory muscle endurance, hospital admissions or days off work or school.