What are the effects of training muscles to influence breathing (in and out) in people with cystic fibrosis?
Cystic fibrosis is the most common genetic disease in white populations and causes problems with the lungs in most people with the condition. Training the muscles that cause the chest to expand and contract may help to improve lung function and the quality of life for people with cystic fibrosis.
The evidence is current to: 11 June 2020.
We searched for studies where people with cystic fibrosis were put into either a group for respiratory muscle training or a control group at random. We included ten studies with 238 people which used a wide variety of training methods and levels. In eight of the studies, the treatment group and the control group each only received either respiratory muscle training or a control treatment (one study had three groups in total: one receiving control treatment and two receiving different levels of training). In one study the participants received both types of treatment, but in a random order. Lastly, one study compared training with usual care. The studies lasted for a maximum of 12 weeks and all were quite small; the largest only had 39 people taking part. The studies included people with a range of ages over six years old, but most seemed to be adults. The studies reported a variety of outcomes. All reported some measure of respiratory muscle strength, and most reported at least one measure of lung function, however only three studies reported on quality of life.
Results could not be combined to answer the review question, because the studies either did not publish enough details or did not use the same standard measurements. No study found any difference in lung function after training, but one of the studies reported an improvement in exercise duration when training at 60% of maximal effort and a further study which trained participants at 80% of maximal effort reported some improvements in quality of life judgements. There was some evidence of an improvement in respiratory muscle function in two studies.
Given this lack of information, a recommendation for or against respiratory muscle training cannot be made. Future studies should look to improve upon the methods of those previously conducted, and should report using standardised measurements.
Quality of the evidence
It was generally unclear how people were split into groups for treatment and whether this would have affected the results. Three studies stated that the people assessing the outcomes did not know which treatment those taking part had received, but this was unclear in other studies. Individuals dropped out of three of the studies for reasons which may be directly related to the treatment and therefore may introduce a risk of bias to the results. One study had no-one drop out and the other six studies did not state how many people dropped out of them. We assessed the quality of the evidence and judged the evidence for lung function, exercise capacity, postural stability and health-related quality of life to be very low quality, but the evidence for respiratory muscle function to be low quality.
There is insufficient evidence to suggest whether this intervention is beneficial or not. Healthcare practitioners should consider the use of respiratory muscle training on a case-by-case basis. Further research of reputable methodological quality is needed to determine the effectiveness of respiratory muscle training in people with cystic fibrosis. Researchers should consider the following clinical outcomes in future studies; respiratory muscle function, pulmonary function, exercise capacity, hospital admissions, and health-related quality of life. Sensory-perceptual changes, such as respiratory effort sensation (e.g. rating of perceived breathlessness) and peripheral effort sensation (e.g. rating of perceived exertion) may also help to elucidate mechanisms underpinning the effectiveness of respiratory muscle training.
Cystic fibrosis is the most common autosomal recessive disease in white populations, and causes respiratory dysfunction in the majority of individuals. Numerous types of respiratory muscle training to improve respiratory function and health-related quality of life in people with cystic fibrosis have been reported in the literature. Hence a systematic review of the literature is needed to establish the effectiveness of respiratory muscle training (either inspiratory or expiratory muscle training) on clinical outcomes in cystic fibrosis. This is an update of a previously published review.
To determine the effectiveness of respiratory muscle training on clinical outcomes in people with cystic fibrosis.
We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group Trials register comprising of references identified from comprehensive electronic database searches and handsearches of relevant journals and abstract books of conference proceedings.
Date of most recent search: 11 June 2020.
A hand search of the Journal of Cystic Fibrosis and Pediatric Pulmonology was performed, along with an electronic search of online trial databases. Date of most recent search: 05 October 2020.
Randomised controlled studies comparing respiratory muscle training with a control group in people with cystic fibrosis.
Review authors independently selected articles for inclusion, evaluated the methodological quality of the studies, and extracted data. Additional information was sought from trial authors where necessary. The quality of the evidence was assessed using the GRADE system.
Authors identified 20 studies, of which 10 studies with 238 participants met the review's inclusion criteria. There was wide variation in the methodological and written quality of the included studies. Four of the 10 included studies were published as abstracts only and lacked concise details, thus limiting the information available. Eight studies were parallel studies and two of a cross-over design. Respiratory muscle training interventions varied dramatically, with frequency, intensity and duration ranging from thrice weekly to twice daily, 20% to 80% of maximal effort, and 10 to 30 minutes, respectively. Participant numbers ranged from 11 to 39 participants in the included studies; five studies were in adults only, one in children only and four in a combination of children and adults.
No differences between treatment and control were reported in the primary outcome of pulmonary function (forced expiratory volume in one second and forced vital capacity) or postural stability (very low-quality evidence). Although no change was reported in exercise capacity as assessed by the maximum rate of oxygen use and distance completed in a six minute walk test, a 10% improvement in exercise duration was found when working at 60% of maximal effort in one study (n = 20) (very low-quality evidence). In a further study (n = 18), when working at 80% of maximal effort, health-related quality of life improved in the mastery and emotion domains (very low-quality evidence). With regards to the review's secondary outcomes, one study (n = 11) found a change in intramural pressure, functional residual capacity and maximal inspiratory pressure following training (very low-quality evidence). Another study (n=36) reported improvements in maximal inspiratory pressure following training (P < 0.001) (very low-quality evidence). A further study (n = 22) reported that respiratory muscle endurance was longer in the training group (P < 0.01). No studies reported significant differences on any other secondary outcomes. Meta-analyses could not be performed due to a lack of consistency and insufficient detail in reported outcome measures.