Comparison of Repetitive Magnetic Stimulation and Exercise on Quadriceps Function in COPD
Comparison of Repetitive Magnetic Stimulation and Exercise on Quadriceps Function in COPD
Background Chronic Obstructive Pulmonary Disease (COPD) patients develop leg weakness and a
 reduced walking capacity, due to reduced leg muscle oxygen-utilising capacity (OUC). Animal
 experiments indicate that low muscle levels of Peroxisome Proliferator-Activated Receptors
 (PPAR) cause the reduced muscle OUC.

 Aims

 In COPD patients, investigate whether:

 1. reduced muscle PPAR levels cause reduced leg muscle OUC, by investigating a correlation
 between these in muscle samples (Study 1).

 2. training increases muscle PPAR levels in proportion to increases in OUC, as should occur
 if PPARs control OUC (Study 2).

 3. muscle PPAR levels and walking capacity correlate (Study 1 and 2).

 3. the new technique of repetitive stimulation of the nerve to the leg with a magnet (rMS)
 improves muscle OUC (Study 2).

 Study 1 Leg weakness and walking ability are assessed in 75 patients, then a leg muscle
 sample is taken to measure PPARs and OUC.

 Study 2 60 Study 1 patients have either cardiovascular training, rMS, or no training, for 8
 weeks, then are re-studied as in Study 1.

 Importance If reduced PPAR levels correspond with leg weakness, medicines can be developed to
 target these receptors and treat weakness. If rMS is effective, it can be offered to
 patients.
There has been considerable interest in finding methods of improving quadriceps function in
 COPD, since quadriceps dysfunction is associated with reduced exercise capacity5 and survival
 in patients16, independently of lung function. Pulmonary rehabilitation (PR) courses
 comprising exercise and education can increase oxidative enzymes, strength and endurance of
 the quadriceps in patients with COPD17 and improve walking capacity even over a period of 8
 weeks12, 18. However, PR is not a complete solution: not all regions of the UK offer PR, PR
 only has on average a 50% uptake rate by patients and the drop-out rate is 30%. Also a
 significant proportion of patients (about 30%) do not increase their exercise capacity as a
 result of PR19, perhaps because breathlessness limits the training they complete or their
 peripheral muscle strength is normal19. Therefore, there is interest in alternative
 treatments or add-ons to exercise, particularly in terms of localised muscle treatments that
 are not limited by impaired respiratory function. Repetitive electrical stimulation of the
 femoral nerve (rES) appears to be an effective alternative method of passively training the
 quadriceps muscle. 30 minutes rES at 10Hz five times a week to both legs increased muscle
 strength and exercise performance in patients with COPD21 and those with heart failure22.
 Similar results have been achieved with fifteen minutes of repetitive magnetic stimulation of
 the femoral nerve (rMS) three times a week23. However, treatment studies with rES to
 investigate effects on exercise performance have often used separate treatment and control
 groups which introduces inter-subject differences into studies already limited by sample
 size243 and have only used voluntary measures of quadriceps function96. The only biopsy study
 of rES used a cross-over design but biopsies were only taken before and after the rES
 training period and not before and after the control period.244 The rMS study involved a
 total of eighteen subjects (ten assigned to rMS, eight to control) and biopsies were not
 taken to evaluate histological changes in the muscle. With this study, I sought primarily to
 evaluate the changes in quadriceps fibre characteristics as a result of an intensive rMS
 protocol, and secondarily, compare changes in quadriceps function as the result of rMS with
 the clinical gold standard for improving muscle function, PR.

 Methods

 Ethical approval The Research Ethics Committee of the Ealing & West London Mental Health
 Trust approved the study (06/Q0410/54). The trial was registered with National Clinical
 Trials Database (NCT 00737698). 2.13.1

 Sample size calculation The sample size required for the training study was based on power
 calculations from a previous study on PR from our group221 and pilot data from our group on
 the effect of rMS on muscle strength (Swallow et al, unpublished) using Stata 10 statistical
 software. The power calculations were based on functional improvements (increase of 54m on
 6MW as a result of PR and 10% increase in quadriceps TwQ as a result of rMS, as the minimum
 clinically significant increments) rather than increases in muscle fibre CSA or type I fibre
 proportions as the data for the latter was not available. We chose an increase of 10% twitch
 force as the minimally significant increment as previous data from Mador et al showed a 9.7%
 increase in twitch force as the result of 8 weeks PR17. A conventional power of 80% with a
 two-tailed p value of ≤0.05 was chosen indicating that a minimum of ten patients were
 required for the PR arm and twenty six for the rMS arm. We aimed to recruit fifteen to the PR
 group and thirty to the rMS group to allow for patient drop-out at the rates we have
 previously encountered. At completion, there were seventeen in the PR group and thirty seven
 in the rMS group.

 Subject selection Eighty six COPD patients consented for the cross-sectional study also
 consented for the training study therefore the inclusion and exclusion criteria were as for
 the cross-sectional study. Patients were precluded from starting any new exercise regimen or
 new regular medication from consent to completion of the study, and patients were encouraged
 to contact me on day 1 of an acute exacerbation so appropriate treatment could be instituted.
 The study design and flow of participants through the study are shown in Fig. 4.1 and 4.2.

 Randomisation FFMI was calculated using bioelectrical impedance (Methods chapter Section
 2.4.2.1) and patients stratified into low FFMI (<15 kg/m2 for females, <16 kg/m2 for males)
 and normal FFMI. The low and normal FFMI groups were randomised separately (so low FFMI
 patients were evenly distributed between treatment groups) using a sealed envelope system and
 a block of 4 procedure weighted 2:1:1 for rMS: PR: no active treatment as the power
 calculation suggested that at least twice as many patients were required in the PR arm as the
 rMS arm.

 Pre-training assessments Lung function, FFMI, quadriceps strength, quadriceps endurance,
 physical activity and 6MW and maximal cycle ergometry performance and HRQOL measurements were
 performed as described in the Methods chapter Sections 2.4-2.7. Percutaneous biopsy of the
 quadriceps and muscle fibre type analysis were performed. Patients underwent the pre-training
 physiological assessment and biopsies within four weeks of randomisation. The assessment was
 as described for the cross-sectional study (in the rMS group both legs were tested on the
 same day, in the other two groups the leg ipsilateral to the dominant hand was tested) and
 then patients proceeded to their allocated treatment within two weeks.

 Training protocols

 Repetitive magnetic stimulation of the femoral nerve (rMS) This was delivered using the
 Magstim Rapid magnetic nerve stimulator system (Magstim, Whitland Dyfed, UK) and supervised
 by myself at RBH Muscle Lab. The patient sat upright or reclined slightly backwards with the
 mat coil wrapped round the body of the quadriceps muscle to be trained, with the foot of the
 leg being stimulated positioned in a strap so that the contractions were isometric (Fig.
 2.8). The stimulation frequency was 40Hz with a duty cycle of 0.4 (1s on, 4s off). Patients
 had three hours continuous rMS (apart from toilet breaks) twice a week over an 8-week period
 with at least twenty four hours rest between sessions. At the first session the stimulus
 intensity was increased from 22% power to 40% power, and subsequent sessions were at 40%
 power as this was the upper limit of what patients could tolerate and the machine could
 deliver for the whole session. 40% power generally generated between 10-20% of the patient's
 MVC.

 Pulmonary Rehabilitation (PR) This was run by a research respiratory physiotherapist at the
 Royal Brompton Hospital twice a week with a maximum of three patients per session so training
 was closely supervised. Training consisted of a warm-up, then one hour aerobic work with
 subjects exercising on a stationery bicycle at a workload that produced 80% of their peak VO2
 on a maximal incremental cycle ergometry protocol, on a treadmill, climbing stairs, and a
 combination of leg resistance exercises involving leg weights, squats and sit-to-stand
 manoeuvres, followed by a cool-down. Attempts were made at each session to increase the
 intensity and/or number of repetitions of each exercise. The exercise sheet used by the
 supervising physiotherapist to chart achievements is shown in Fig. 2.9.

 No active treatment (Controls) Controls were asked to continue with their usual activities
 and were contacted by telephone two to three times during the 8-week period to minimise
 drop-out and to monitor for acute exacerbations of COPD. After study completion, these
 patients were enrolled on the PR course at RBH if they wished.

 Post-training assessments For the PR and rMS groups, the physiological tests were done four
 to five days after the last training session, and three to four days later the biopsies were
 taken. Controls were assessed in the same week as the others. The timing was aimed at
 minimising group differences from varying delays between the last training session and
 testing. Post-training assessments involved all the same tests as the pre-training
 assessment.

 Statistical analysis The primary outcomes measures were a) change in quadriceps fibre
 proportions and fibre CSA in trained leg versus untrained leg in rMS group and b) change in
 quadriceps function in rMS group versus PR group. All statistical analysis was performed
 using SPSS (SPSS 15, Chicago, USA). The Mann-Whitney U test was used to assess group
 differences (patients vs controls, trained vs untrained leg, change in trained leg vs change
 in untrained leg), Spearman's rank correlation coefficient was calculated to assess
 correlations and the Wilcoxon Signed-Ranks test used to examine differences between pre and
 post-training results in both the trained and the untrained leg (data not normally
 distributed). An interaction factor was calculated to assess the effect of exacerbation
 during the study. A two-tailed p value of ≤0.05 was used to define statistical significance.
Inclusion Criteria:

 -  Chronic Obstructive Pulmonary Disease

 Exclusion Criteria:

 -  Cardiac failure

 -  Renal failure

 -  Liver failure

 -  Diabetes mellitus

 -  Systemic inflammatory diseases eg Rheumatoid arthritis, SLE

 -  Warfarin, coagulation problems