Effects of Inspiratory Muscle Training on Dyspnea Perception During Exercise in Patients With COPD

Overview

Patients with chronic obstructive pulmonary disease are often limited in their exercise capacity by intolerable shortness of breath (dyspnea). Patients are breathing at high lung volumes during exercise which forces inspiratory muscles to work at a high percentage of their maximal capacity. This increased inspiratory effort has been shown to be independently related to symptoms of dyspnea during exercise in previous research. Eight weeks of high intensity variable flow resistive inspiratory muscle training is hypothesized to reduce inspiratory effort and to decrease neural drive to inspiratory muscles. These factors are hypothesized to jointly contribute to delaying the occurrence of intolerable symptoms of dyspnea and to improve exercise tolerance in these patients.

We want to study whether a highly intense inspiratory muscle training program improves exercise capacity by reducing inspiratory effort, improving pulmonary mechanics and delaying the development of intolerable symptoms of dyspnea during cycle exercise. Eight weeks of high intensity variable flow resistive inspiratory muscle training is hypothesized to reduce inspiratory effort and to decrease neural drive to inspiratory muscles. The ratio of inspiratory effort to volume displacement should improve, and reductions of inspiratory capacity during exercise should be delayed. These factors are hypothesized to jointly contribute in delaying the occurrence of intolerable symptoms of dyspnea and to improve exercise tolerance in these patients. We will study physiological mechanisms by which inspiratory muscle training exerts its effects on dyspnea reduction and exercise capacity. In this clinical trial patients will be randomly allocated into either an intervention or a control group. The intervention group will receive a highly intense inspiratory muscle training program that will improve inspiratory muscle function. The control group will receive a sham training that will not result in physiological benefits. During the 8-week training period patients will have to attend the hospital once weekly for a short visit to perform a training session under supervision. Before the training intervention patients will be assessed twice and then again once after the 8-week program. This means that this trial will involve a total of 11 visits (3 long visits (approximately 4h) for assessments and 8 short visits (approximately 30 minutes) for supervised training sessions) over a period of 2-3 months. Assessments of pulmonary function, inspiratory muscle function, exercise capacity, daily physical activity and symptoms of dyspnea during exercise will be performed. Pulmonary mechanics and inspiratory muscle activation during exercise will also be assessed. Stable COPD patients with pronounced inspiratory muscle weakness (Pi,max \< 70cmH2O or \<70% predicted) will be eligible to participate in the study. Exclusion criteria will be diagnosed psychiatric or cognitive disorders, progressive neurological or neuromuscular disorders and severe orthopedic problems having a major impact on exercise capacity. Patients in both the intervention and the placebo group will follow an eight-week IMT program. They will receive either high intensity IMT (intervention group) or sham IMT (placebo group). Interventions will be presented to patients as strength training (intervention group) or endurance training (placebo group). Measurements of primary and secondary endpoints will be performed before and after 8 weeks of IMT. All tests will be performed by an experienced investigator that will be blinded to group allocation. Total training load for both groups will be two to three daily sessions of 30 breaths (3-4 minutes per session), on 7 days per week, for 8 weeks. IMT will be performed using a variable flow resistive loading device(POWERbreathe®KH1, HaB International Ltd., Southam, UK). Differences in primary and secondary outcomes between groups after 8 weeks of IMT will be compared adjusting for baseline differences in an analysis of covariance (ANCOVA). Dyspnea perception on a 10-point Borg Scale (BORG CR10) at identical ventilation during the constant work rate cycling test after the intervention will be the primary outcome. To detect a difference of one point in the dyspnea perception on a 10-point Borg Scale at identical ventilation during the constant work rate cycling test after the intervention between subjects, assuming a standard deviation of the changes in dyspnea perception between baseline and follow-up measurement of 1 point with a degree of certainty (statistical power) of 80% and a risk for a type I error (a) \< 5%, a sample size of 16 patients for each group is needed. These estimates are based on previous work on dyspnea perceptions during exercise.