Study design
The trial was carried out at Zhujiang Hospital of Southern Medical University from January 2015 to December 2017. The protocol was approved by the Zhujiang Hospital ethics committee(number: 2016-HXNK-005), and consisted with the Declaration of Helsinki. Informed consents were signed and obtained from all the subjects before the trial. Prior to the trial, it was registered on ClinicalTrials.gov (identifier: NCT02326181). Report of this trial was consistent with the Consolidated Standard of Reporting Trials statement [14].
Recruitment of subjects
During a run-in period for 2 weeks, Patients with clinically stable COPD [15], naive to pulmonary rehabilitation and willing to participate were eligible. Patients got excluded if they had cognitive disorders, organ failure, malignant tumors, or metabolic diseases.
Of the 225 COPD subjects initially enrolled, 92 subjects were recruited and randomly allocated to Sham training, IMT, CTSC, and CTDC, according to a computer-generated sequence using a simple randomization method (Fig. 1). The randomization list was concealed in sequentially numbered, sealed, opaque envelopes and prepared by an independent physician not involved in subject recruitment. Each new subject was assigned a number sequentially, then the corresponding envelope was opened to decided which group they would enter. Before allocation, subjects learned all kinds of training. Subjects continued their regular medications during the study, and had the right to withdraw at any time.
Study interventions
Subjects in all groups trained daily, with each session lasting for 48 minutes per day, 7 days a week, 8 weeks. The training was performed mainly at home, each set consisting of 3 minutes of training and 2 minutes of rest. Sham training performed 16 sets of no-load respiratory muscle training daily. IMT performed 8 sets of inspiratory muscle training and 8 sets of no-load respiratory muscle training per day. CTSC performed 16 sets of combined training in one respiratory cycle daily. CTDC performed 8 sets of inspiratory muscle training and 8 sets of expiratory muscle training separately in different cycles daily.
A modified threshold trainer with a monitoring device was used (Fig. 2-A). The modified trainer consisted of a threshold inspiratory trainer(Threshold IMT, Respironics, USA) and a threshold expiratory trainer(Threshold PEP, Respironics, USA), which were connected to a tube (Fig. 2-B) with two one-way valves(pattern ID:CN201721194926.4). Threshold trainers featured with an adjustable specific load [16]. Threshold PEP would be removed from the modified trainer to perform IMT. Threshold IMT would be removed to perform EMT. For sham training, both trainers would be removed. The load range of the modified trainer consisted with Threshold IMT(9-41 cmH2O) and Threshold PEP(5-20 cmH2O).
For training management, a monitoring device(pattern ID:CN201620070450.2) was installed (Fig. 2-C). The device recorded daily use including frequency and duration. Before training, subjects connected the device to a wireless terminal (such as a smart phone) through Bluetooth,which recorded daily use. The records were reviewed by staffs weekly. If a subject did not finish the planned assignment, they would take a lengthened training as compensation. Subjects were required to record, if any, discomfort during training. If their situation exacerbated, subjects would withdraw for treatment. Besides, Subjects received follow-up by telephone weekly and in the clinic every 2 weeks. In the clinic follow-up, Staffs checked the discomfort record, re-measure PImax and PEmax for load reset. The inspiratory load started at 30% PImax, and incrementally increased 5% every two weeks until reaching 45% PImax. The expiratory load was adjusted from 15% PEmax plus 5% PEmax every two weeks to 30% PEmax.
Endpoints
The primary endpoint was respiratory muscle strength. The secondary endpoints were dyspnea, breathing pattern, spirometry, exercise capacity, quality of life, emotional status, BODE index, and nutritional status. Endpoints were measured before the start of intervention (as baseline) and within 7 days after its completion. All tests were performed by one same experienced respiratory physician blinded to the allocation.
Respiratory muscle strength
Examination of respiratory muscle function consisted of measuring PImax and PEmax with a digital gauge (AZ-8205, AZ Instrument, Taiwan). Maximum value of three available tests that varied by less than 20% was recorded. The interval of each measurement lasted at 30 seconds at least. The lower limit of normal PImax was 60 cm H2O [17].
Dyspnea
The modified Medical Research Council (mMRC) dyspnea scale was adopted to evaluate the severity of breathlessness.
Breathing pattern
Breath flow rate was measured using a pneumotachograph (MLT300L, ADInstruments, Australia). Respiratory rate (RR), inspiratory time (Ti), expiratory time (Te), inspiratory time/total breath cycle duration (Ti/Ttot), tidal volume (Vt), and inspiratory capacity (IC) were acquired via calculating the flow rate.
Spirometry
Spirometry was measured using a spirometer (PonyFX 229, Cosmed, Italy) which was calibrated daily according to the 2014 ATS guidelines [18]. Forced expiratory volume in one second (FEV1), percent-of-predicted FEV1(FEV1%), forced vital capacity (FVC), and FEV1/FVC were recorded before a bronchodilator test.
Exercise capacity
Exercise capacity was assessed with 6-minute walk test (6MWT). During the test, heart rate and blood oxygen saturation were monitored by pulse oximetry. Oxygen saturation of all subjects was maintained at more than 90%.
Quality of life, emotional status
Quality of life was reflected by St George’s Respiratory Questionnaire (SGRQ) and COPD Assessment Test (CAT) [19]; Hospital Anxiety and Depression Scale (HADS) were used for evaluation of emotional status.
Nutritional status
Nutrition was reflected by BMI (body mass/height2) and FFMI (fat-free mass/height2). A FFMI ≤ 15 kg/m2 in women and FFMI ≤ 16kg/m2 in men was defined as low FFMI.
BODE index
The BODE index consists of BMI (B), airflow obstruction (O), dyspnea (D), and exercise capacity (E), which was used for a comprehensive evaluation of the subjects.
Statistical analysis
A value of P < 0.05 was considered statistically significant. For subjects who withdrew, an intention-to-treat analysis was done. The last observation carried forward method was used for data filling. Data were presented as mean ± standard deviation (SD) or mean ± standard error (SE) and analyzed via SPSS 20.0 (SPSS Inc., Chicago, USA). One-way analysis of variance (ANOVA) was applied for baseline comparison. A covariance analysis (ANCOVA) was adopted to analyze the differences (after minus before, shown as Δ) of each index, and models of least-significant difference were used for the baseline analysis. Differences in breathing patterns among groups and pre- and post-test comparisons were analyzed using mixed linear model. Subgroup analyses were performed using two-way ANOVA.