Would Integrating Inspiratory Muscle Training Into Pulmonary Rehabilitation of Adults With Burn Injuries Have Any Advantageous Effects? A Randomized, Double-Blind, Sham-Controlled Study
Article information
Abstract
Objective
To determine the effectiveness of adding inspiratory muscle training (IMT) alongside a pulmonary rehabilitation protocol in terms of inspiratory muscle strength, lung function, and exercise capacity in burned adults.
Methods
A randomized, double-blinded, sham-controlled study. Fifty-two adult patients with burn injuries, more than 20 years old and at least 20% total body surface area, were assigned randomly either to the experimental or the conventional group. The participants in the experimental group were given IMT plus a pulmonary rehabilitation program; the conventional group received only a pulmonary rehabilitation program. The interventions were performed for 8 weeks. At the beginning and after 8 weeks of training, the respiratory muscles’ strength, lung function and exercise capacity were all examined.
Results
After 2 months of training, the experimental group demonstrated statistically significant improvements than conventional group in maximum inspiratory pressure, maximum expiratory pressure, 6-minute walk test, forced vital capacity, and forced expiratory volume in 1 second (p<0.05).
Conclusion
An 8-week IMT program coupled with pulmonary rehabilitation increases respiratory muscle strength, pulmonary functions, and functional capacity in burn patients. IMT is a beneficial and efficient therapy that can be easily implemented for burn patients.
INTRODUCTION
Burns are life-threatening and devastating injuries that can impair functional exercise capacity, decrease pulmonary function, reduce muscle strength and endurance, and impede normal daily activities [1-6]. As the recovery rates following burn injuries gets higher, serious challenges and significant physical limitations that have a detrimental impact on quality of life and health emerge in the later stages of injury, following the acute stage [2,4,6].
Burned patients have impaired pulmonary function for up to years post burn injury and presented with either restrictive or obstructive pulmonary deficits [1-3]. Respiratory complications are responsible for 41% of mortality and morbidity rates among burned adults [7]. Sixty-nine percent of the burned were later diagnosed with pulmonary deficits, even though none of them experienced pulmonary deficits prior to injury [8].
Burn-injured patients have impaired pulmonary function, lower exercise capacity, and higher desaturation of oxygen during exercise compared to healthy controls. They also stated that these limitations lasted five years following the injury [2]. The hypermetabolic condition linked to major burns, an extended duration of no physical activity during the convalescent stage, and altered pulmonary functions may all contribute to the decrease of respiratory muscle performance and exercise capacity [1,4,5].
Hospital discharge marks the starting point of an important phase in which these individuals reintegrate back to their pre-burn lives. Rehabilitation interventions for sustained recovery in burn patients focus on promoting physical functioning and independence in routine tasks [6,9]. Even though the effect of pulmonary rehabilitation combining resistive and aerobic activities on pulmonary function, aerobic capacity, and muscle strength after burn trauma have been established [1,6,10,11]. Evidence on the effect of inspiratory muscle training (IMT) after acute stage remains scarce.
While research on the reduction of respiratory muscle strength post burns is well recognized [4-6], exercise for respiratory muscle strength is often overlooked. Therefore, a personalized pulmonary rehabilitation, including inspiratory muscle strengthening was recommended [4,5]. Additionally, IMT should be investigated beyond the acute phase of injury. As a result, the main focus of the current investigation was to determine the effectiveness of adding IMT alongside a pulmonary rehabilitation protocol in terms of inspiratory muscle strength, lung function, and exercise capacity in burned adults.
METHODS
Study design
A randomized, double-blinded, sham-controlled, study design was applied. The protocol has been approved by Cairo University’s Research Ethics Committee for Physical Therapy (PT.REC/012/004201). The methodologies utilized in this investigation adhered to the Declaration of Helsinki’s as well as the CONSORT statement guidelines. The CONSORT statement provided an entire foundation for every aspect of the research procedure, including design of the study, gathering data, and results reporting. Participants received details about the study (i.e., goals, clinical procedures, advantages, and potential difficulties) prior to participation and written informed consent was obtained. The investigation protocol was registered at ClinicalTrials.gov (NCT06315712).
Participants
Fifty-two burn-injured adults who were refered to Cairo University's Faculty of Physical Therapy outpatient clinic for the first time following acute phase therapy from various hospitals in Cairo, Egypt. Participants aged more than 20 years, all of them were healing from injuries that affected at least 20% of their total body surface area (%TBSA). Partial or full thickness burns that either recovered spontaneously or healed by skin grafting. Patients were excluded if they smoked, had open or unhealed wounds, had a known neurological impairment, neuromuscular illnesses, musculoskeletal anomalies, lung, or cardiac diseases, or were unable to exercise regularly.
Sample size
To eliminate type II error, the sample size estimate was performed prior to the initiation of the investigation. G*Power statistical program (version 3.1.9.2) estimated sample size using (F tests- MANOVA: repeated measures, within-between interaction, α=0.05, power=90%, effect size=0.5). The effect size was determined using unpublished findings from a pilot study (5 participants in each group). As a result, the minimum sample size was forty-five participants. To compensate for the drop-off, an extra 15% in the calculated sample size was taken into account, resulting in a study sample size of 52 individuals.
Randomization
Fifty-two burn patients were randomly assigned to either respiratory muscle training combining with pulmonary rehabilitation (experimental group) or pulmonary rehabilitation (conventional group) using a computer-generated block randomization algorithm available at http://www.jerrydallal.com/random/randomize.htm. To eliminate biases and variation between the two groups, participants were randomly assigned to block sizes of 4, 6, and 8, with a 1:1 allocation ratio. The author, who was not involved in recruiting, data collection, or the treatment, oversaw handling the randomization process. Randomization codes were stored in sealed opaque envelopes and consecutively marked to ensure masked allocation. The treating researcher unsealed the envelope and proceeded with therapy based on group allocation. A researcher who was blinded to group randomization collected data at baseline and 8 weeks after the intervention.
Intervention
Everyone who participated in the experimental and conventional groups went through a similar pulmonary rehabilitation program, which consisted of five weekly sessions for eight weeks. Both groups had the same exercise frequency and duration. All exercise sessions were conducted on a case-by-case basis, with supervision. Participants warmed up on the treadmill for five minutes at their own pace, and major muscle groups were stretched at the end of each exercise session. The pulmonary program was: four resistive exercises, aerobic training, and deep breathing exercises. The four primary resisted exercises consisted of four sets of upper- extremity exercises (chest press and biceps curls) and lower-extremity exercises (leg press and knee extension). All exercises were completed with varying resistance equipment. The resistance training equipment has five stages and is conducted at 50%–80% (8–12 repetitions) from the level corresponding to maximum strength [6,12]. Loading intensity was modified biweekly based on maximum strength tests. Aerobic conditioning activities on the treadmill were also included in the schedules. When the participants reported a dyspnea sensation on the Borg scale, the intensity was maintained [6,13]. Resistance training (30 minutes per session) and aerobic exercise (30 minutes per session) were carried out five days a week, each lasting one hour. Participants got instructions to practice deep breathing exercises. Throughout aerobic and resistance training, oral instructions were provided, and deep expiration and inspiration were carried out without urging abdomen retraction [6].
Patients in the experimental group underwent IMT in addition to pulmonary rehabilitation. The POWERbreathe equipment (POWERbreathe International Ltd.) was employed for improving inspiratory muscle strength. It is a respiratory muscle enhancer that employs resistance training principles. Strengthening the inspiratory muscles using POWERbreathe functions similarly to weightlifting in strengthening other muscle groups in the body. The use of this equipment increases the endurance as well as strength of the inspiratory muscles. Initially the participants tried three sets of 30 breaths on the POWERbreathe to adjust the load and become familiar with the device. The training included six 30-breath sets each day, divided into two sessions each. There is a one-minute rest time between each set. Training was scheduled five days a week for eight weeks. In the experimental group, the inspiratory muscle load for training was 50% of maximum inspiratory pressure (MIP), and it was reviewed and changed weekly. The conventional group trained the inspiratory muscles at a set load (5% of MIP), with weekly evaluations but no readjustments [14].
Outcome measures
The MIP was the primary outcome, while the maximum expiratory pressure (MEP), pulmonary function, and 6-minute walk test (6MWT) were the second outcomes. All the outcomes measured before and after eight weeks. To guarantee objective outcome assessment, the assessors were blinded to the intervention allocated to each participant and were not involved in its administration. Before data collection session, each participant received an orientation session to acquire knowledge about the procedures for evaluation and how to conduct appropriate assessments. At baseline, participants’ demographics were collected, including age, gender, weight, height, body mass index, TBSA, number of surgeries, cause of burn, depth of burn, number of chests burns and inhalation injuries, and time since burn injury.
MIP and MEP were measured during maximal respiratory effort to determine respiratory muscle strength. The assessment was conducted using an electronic respiratory pressure meter (Micro RPM; Micro Medical) in accordance with the American Thoracic Society (ATS) and European Respiratory Society (ERS) regulations. The subjects repeated the respiratory muscular strength test 3–5 times until there was at least a 10% difference between the values. The highest value was recorded and analyzed. The MIP and MEP values are reported in cmH2O [15].
Pulmonary function assessment was performed with a mobile spirometer following ATS and ERS recommendations. At the completion of the pulmonary function test, the forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and FEV1/FVC ratio were calculated. The spirometer reports the results of the pulmonary function test in liters [16].
The 6MWT assessed participants’ functional exercise capacity. The 6MWT was performed using standard instructions based on the ATS recommendations. The individuals were instructed to walk as quickly as they could for 6 minutes along a straight hallway of 30 meters. At the end of the test, the 6MWT distance was measured [17].
Statistical analysis
The statistical analysis was carried out using IBM SPSS software for Windows, version 25.0 (IBM Corp.). It was carried out with the intention to treat analysis, the data missed from the eighth-week measurements using the multiple imputation approach. Descriptive statistics were computed for each group at baseline and after 8 weeks. The Shapiro–Wilk test is used to determine the normal distribution of data. Two-way mixed model of multivariate analyses of variance, with the time is within subject factor, were utilized to determine any differences between the mean change scores of each group regarding MIP, MEP, 6MWT, FVC, FEV1, and the FEV1/FVC ratio at each time interval. The F-value was calculated using Wilks’ lambda. If the MANOVA showed a significant effect (p<0.05), a follow-up univariate ANOVAs were conducted. To avoid the risk of a type I error, multiple comparisons were done with Bonferroni correction. All statistical tests had a level of significance of p<0.05.
RESULTS
Fig. 1 depicts the patient flow diagram used throughout the trial. Table 1 shows the baseline demographic and clinical data for all participants in the experimental and conventional groups. A two-way mixed design multivariate analysis was used to compare the magnitude of variation in values on all outcome measures between experimental participants and conventional participants. Significant multivariate effects were identified for the impact of therapy, Wilk’s λ=0.48; F(6, 45)=8.12, p<0.001, ƞ2=0.52, for time, Wilk’s λ=0.05; F(6, 45)=144.17, p<0.001, ƞ2=0.95; and the interaction of treatment and time Wilk’s λ=0.25; F(6, 45)=23.15, p<0.001, ƞ2=0.76.
CONSORT 2010 flow diagram.
Baseline demographic and clinical characteristics of subjects (N=52)*
Follow-up univariate ANOVAs showed significant change for MIP, F(1,50)=9.4, p=0.003, ƞ2=0.16; for MEP, F(1,50)=11.4, p=0.001, ƞ2=0.19; for 6MWT, F(1,50)=14.62, p=0.001, ƞ2=0.23; for FVC, F(1,50)=30.42, p<0.001, ƞ2=0.38; for FEV1, F(1,50)=53.23, p<0.001, ƞ2=0.52; and for FEV1/FVC ratio, F(1,50)=4.76, p=0.03, ƞ2=0.09.
The results revealed no statistically significant variations between groups in terms of MIP, MEP, 6MWT, FVC, FEV1, and FEV1/FVC ratio at baseline (p>0.05). Table 2 and Fig. 2 demonstrate statistically significant changes between groups following 8 weeks of the intervention for all outcome measures (p<0.05). Table 3 shows that after 8 weeks of treatment, there were statistically significant differences in all outcome measures (p<0.05) in each group, except for the FEV1/FVC ratio (p>0.05).
Clinical characteristics of subjects in both groups after 8 weeks (N=52)*
Clinical characteristics of subjects in both groups after 8 weeks. (A) Maximum inspiratory pressure (MIP). (B) Maximum expiratory pressure (MEP). (C) Six-minute walk test (6MWT). (D) Forced vital capacity (FVC). (E) Forced expiratory volume in 1 second (FEV1). (F) FEV1/FVC.
Within group comparisons for the two groups at baseline and after 8 weeks*
DISCUSSION
The current research has demonstrated that IMT combined with pulmonary rehabilitation is more successful than pulmonary rehabilitation alone in increasing pulmonary function, respiratory muscle strength, and exercise capacity in adult burned patients following hospitalization stage of injury. These findings agreed with previously published studies on burned patient in acute stage, burned children and inhalation injuries [5,18,19], or populations with different conditions for increasing inspiratory muscle strength and improvement in exercise capacity [14,20-24]. Although the impacts of IMT have been tested in several studies, [14,20-24], there remains a lot of curiosity in the effects of such a therapy strategy on adult burned patients following the hospitalization stage of injury. As a result, the findings presented herein may add to the body of evidence supporting the efficacy of IMT in burn trauma.
The American College of Chest Physicians/American Association of Cardiovascular and Pulmonary Rehabilitation Committee has supported IMT as a component of pulmonary rehabilitation [21]. Furthermore, the ERS agreement advises IMT in conjunction with a standard pulmonary rehabilitation program for individuals with inspiratory muscle weakness. This advice depends on the findings from multiple meta-analyses [22,23], which indicated that IMT improved inspiratory muscle strength and endurance, as well as exercise capacity in the 6MWT.
The experimental group had a mean MIP of 75.62±16.47, while the conventional group had a mean MIP of 72.69±11.67. At baseline, adult burn injured participants had significantly reduced respiratory muscle strength than healthy controls [4]. This contradicts the ATS and ERS, which state that MIP below 80 cmH2O indicates inspiratory muscle weakness [15]. In our investigation, patients attained a statistically significant improvement in MIP of 20 cmH2O in the experimental group, which is greater than the minimal clinically important difference value of 13 cmH2O [23]. This result demonstrated an improvement in inspiratory muscular strength, which was consistent with findings from earlier research on older subjects [20], chronic obstructive pulmonary disease [21-23] and asthmatic patients [24].
In addition to MIP, MEP levels increased in the experimental group. The latter finding can be clarified through neural conditioning caused by repeated exposures to the same task (learning effect), which is a mechanism that increases respiratory muscle strength by enhancing neuromuscular recruitment patterns [20]. These findings can be attributed to the fact that the process of adaptation to training is dependent on an increase in the ratio of type I fibres and the size of type II fibres, which directly alters the length-tension relationship that governs the respiratory system’s force-generating mechanics [25]. Furthermore, a training regimen like the one presented here results in increased diaphragm neural activation and chest wall muscle recruitment [26]. According to Komi [27], increases in muscle strength after brief bouts of training with progressive loads seem to be caused by improved intra- and intermuscular neural adjustment. These methods improve synchronization in the frequency of neuromuscular firing, resulting in higher motor unit activation. Whatever of the cause, it is believed that increasing the strength of the respiratory muscles may help enhance exercise capacity and reduce the incidence of respiratory infections and hospitalization due to increased expiratory force, which leads to more efficient coughing [20].
In line with our results, previous research suggests that IMT in combination with other exercise trainings improves functional exercise capacity more than exercise training alone in patients with chronic obstructive pulmonary disease [21,22]. In our investigation, a rise of 55 m in the 6-minute walking distance exceeds the literature’s minimal clinically important difference [23]. The consequences are partly attributed to the reduction of the respiratory metaboreflex caused by IMT. The metaboreflex hypothesis has been developed to explain respiratory muscle training ergogenic effects. In brief, the metaboreflex theory proposes that fatigued respiratory muscle contractions during high-intensity exercise increase sympathetic output, restricting leg blood flow and performance during exercise. higher tolerance to respiratory muscle fatigue would thus attenuate the response, resulting in decreased sympathetic output, higher leg blood flow, and improved endurance performance [28,29].
A number of studies have found that patients with burns have lower FVC and FEV1 values than healthy people [1-4]. In our research, patients accomplished a statistically significant rise of 21.74% in FVC and 23.96% in FEV1, which additionally ended in a better FEV1/FVC ratio. It is probable that IMT enabled the diaphragm and respiratory muscles to perform more work, resulting in an improvement in respiratory capacity and an increase in thoracic expansion, which had a role in raising static and dynamic lung volumes [30].
The conventional group (sham IMT) was designed to meet the real placebo criteria described by Ojanen [31], which state that placebo therapy should be relevant to participants, inactive, and generate expectations, participation, and subjective utility. For this investigation, we used the lowest possible training load (5% of MIP). As a result, it is possible that our procedure met the previously stated placebo criterion. The placebo group showed considerable post-treatment improvement in exercise capacity, respiratory muscle strength, and pulmonary function. The resulting improvements could be attributable to the effects of respiratory exercises, that may have encouraged a better controlled respiration pattern, better thoracic mobility, higher diaphragmatic strength, and improved respiratory efficiency. Another potential cause is the psychological impact of placebo IMT. Preparation as well as expectations may have served an important role in enhancing outcomes, particularly since the participating youngsters had been receiving regular placebo training for two months [31].
Unfortunately, we did not evaluate the subjects’ physical activity levels, which may have influence on the improvements of all measurement’s; this parameter should be included as an outcome in further studies. Inability of follow-up with volunteers in the months following the training prevented evaluation of IMT’s long-term efficacy. Future research should investigate burn trauma factors (degree of burn, location, TBSA and inhalation injury, etc.) that may influence respiratory muscle strength and pulmonary function in burn patients.
Conclusion
In this study, we demonstrated that eight weeks of IMT in addition to pulmonary rehabilitation increases respiratory muscle strength, pulmonary function, and functional capacity in burn patients. IMT is a safe and efficient therapy that can be easily implemented in the rehabilitation program for burn victims. However, more evidence is needed to draw more consistent results.
Notes
CONFLICTS OF INTEREST
No potential conflict of interest relevant to this article was reported.
FUNDING INFORMATION
None.
AUTHOR CONTRIBUTION
Conceptualization: Abdel-Aal NM, Kamel FH. Data curation: Basha MA, Aloraini SM, Kamel FH. Formal analysis: Abdel-Aal NM. Investigation: Abdel-Aal NM, Basha MA, Kamel FH. Methodology: Abdel-Aal NM, Azab AR, Kamel FH. Project administration: Basha MA, Resources: Basha MA, Aloraini SM, Azab AR. Software: Basha MA, Aloraini SM. Supervision: Abdel-Aal NM, Kamel FH. Validation: Abdel-Aal NM, Azab AR. Visualization: Basha MA, Aloraini SM. Writing – original draft: Abdel-Aal NM, Basha MA, Kamel FH. Writing – review & editing: Abdel-Aal NM, Basha MA, Aloraini SM, Azab AR, Kamel FH. Approval of final manuscript: all authors.