Inspiratory muscle training in patients with chronic obstructive pulmonary disease (COPD)

Abstract

An important clinical manifestation of chronic obstructive pulmonary disease (COPD) is impaired exercise capacity due to dyspnea and limb muscle weakness. Respiratory muscle dysfunction is also frequently observed in patients with COPD and is related to dyspnea and exercise limitation. Inspiratory muscle training (IMT) has been applied during pulmonary rehabilitation in COPD patients. However, even after decades of research the role of the respiratory muscles in the rehabilitation program of these patients remains controversial. It is still unclear whether the addition of IMT to a general exercise training program can lead to additional gains in clinically relevant outcomes. This has been attributed to methodological shortcomings and considerable heterogeneity among the several small, single center clinical studies that have been performed and published so far. From meta-analysis it was concluded that IMT might be most effective in patients with pronounced inspiratory muscle weakness. In this PhD project, we investigated a newly developed device for IMT that provides a tapered flow resistive loading (TFRL) and allows for controlling training quality during the IMT sessions. We observed significantly larger increases in inspiratory muscle strength and endurance, as well as changes in breathing pattern during endurance loaded breathing tasks after TFRL-IMT in comparison to the conventionally applied mechanical threshold loading IMT. We also found that patients participating in a combined general exercise training and IMT intervention achieved favorable changes in breathing pattern (breathing deeper and slower) during exercise in comparison with patients participating in rehabilitation without added IMT. The additional benefits of IMT as an adjunct to a general exercise training program on outcomes beyond respiratory muscle dysfunction in patients with COPD were examined in a large multicenter randomized double-blind controlled trial. Superior improvements in inspiratory muscle function did not translate into additional improvements in 6 minute walking distance. However, a larger improvement was observed in endurance cycling time, as well as reductions in dyspnea symptoms at iso-time during the cycling test. The training quality indices (both external work and power achieved during the IMT sessions) and training intensity (and not compliance) were significantly related to improvements in inspiratory muscle strength which in turn was related to improvements in endurance cycling time. We also reviewed potential physiological mechanisms explaining effects of IMT on exercise capacity and dyspnea in patients with COPD and have identified areas in which further research would be warranted. This fundamental knowledge will be a guideline incorporating inspiratory muscle training into evidence-based treatment recommendations for clinical practice and will provide insights for future research on inspiratory muscle training in patients suffering from respiratory muscle dysfunction.TABLE OF CONTENTS Chapter 1 General introduction and rationale 13 1.1 General introduction 15 1.2 Introduction to the presented chapters and objectives of the studies 23 1.3 References 27 Chapter 2 Efficacy of a novel method for inspiratory muscle training in people with chronic obstructive pulmonary disease 31 2.1 Abstract 33 2.2 Introduction 34 2.3 Materials and methods 35 2.4 Results 41 2.5 Discussion 44 2.6 References 48 Chapter 3 Inspiratory muscle training improves breathing pattern during exercise in COPD patients 51 3.1 Abstract 53 3.2 Introduction 54 3.3 Materials and methods 55 3.4 Results 57 3.5 Discussion 62 3.6 References 65 Chapter 4 Chapter 4.1: Inspiratory muscle training protocol for patients with chronic obstructive pulmonary disease (IMTCO study): a multicentre randomised controlled trial 67 4.1.1 Abstract 69 4.1.2 Article summary 70 4.1.3 Introduction 71 4.1.4 Materials and methods 72 4.1.5 Discussion 80 4.1.6 References 81 Chapter 4.2: A multicentre, randomised, double-blind, controlled trial of adjunctive inspiratory muscle training for patients with chronic obstructive pulmonary disease (IMTCO) 85 4.2.1 Abstract 87 4.2.2 Introduction 88 4.2.3 Materials and methods 89 4.2.4 Results 91 4.2.5 Discussion 98 4.2.6 References 103 4.2.7 Data supplement 106 Chapter 5 Respiratory muscle function and exercise limitation in patients with chronic obstructive pulmonary disease (COPD) : A Review 109 5.1 Abstract 111 5.2 Introduction 112 5.3 Load-capacity balance of the respiratory muscles, dyspnea, and exercise limitation in COPD patients 113 5.4 Therapeutic approaches to decrease the load on the respiratory muscles and to improve respiratory muscle capacity 121 5.5 Potential physiological mechanisms explaining effects of improvements in respiratory muscle function on exercise capacity and dyspnea 124 5.6 References 129 Chapter 6 General discussion, future directions and conclusions 139 6.1 General discussion and future directions 141 6.2 General conclusions 152 6.3 References 154 Summary 157 Samenvatting 161 Bijstellingen 165 Short curriculum vitae 169 Publications 173nrpages: 177status: publishe