Self-Administered High Frequency Chest Wall Oscillation Technique for Mucus Clearance in COPD: An Exploratory Pilot Project Using the SMARTVEST Device

1.1 Background

Chronic obstructive pulmonary disease (COPD) is a major health problem across the world and its medical, societal and economic impacts continue to grow. COPD is characterized by chronic obstruction of expiratory flow affecting peripheral airways, associated with chronic bronchitis (mucus hypersecretion with goblet cell and submucosal gland hyperplasia) and emphysema (destruction of airway parenchyma), together with fibrosis and tissue damage, and inflammation of the small airways1. The beneficial effects of smoking cessation in slowing the decline in lung function and the progression of disease have been clearly established. Whether other factors such as mucus hypersecretion, respiratory infections and airway hyper-reactivity contribute to disease progression independent of cigarette smoking is still being debated2.

Patients with COPD are often distressed by mucus hypersecretion which is one of the hallmarks of the disease but little is known about the impact of current therapies on mucus hypersecretion due to the logistical challenges of objectively quantifying mucus in clinical studies 3. Mucus hypersecretion occurs as a direct result of airway inflammation. Neutrophils that die by necrosis disgorge proteases and reactive oxygen species into the lumen. It is concluded that neutrophil death via necrosis leads to the high concentrations of free neutrophil elastase and reactive oxygen species in the sputum of patients with airway neutrophilia and mucus hypersecretion. Inflammatory cells (neutrophils), molecules (neutrophil elastase and reactive oxygen species), signaling pathways (EGFR), and cellular processes (neutrophil necrosis) contribute to mucus hypersecretion in COPD4.

Mucus hypersecretion leads to increased work of breathing, reduced exercise tolerance, deteriorating lung function and increases dyspnoea and cough. Often the mucus hypersecretion also interferes with nocturnal sleep and has a further negative impact on health related quality of life. Combined mucus hypersecretion, reduced clearance, and impairment of the lung defence mechanisms explain why COPD patients even with stable condition, carry potential respiratory pathogens in significant concentration, paving the way for infection and acute exacerbations of COPD5;6. In the natural history of COPD chronic mucus hypersecretion is thought to be linked to the accelerated decline of forced expiratory volume in one second (FEV1)5 7 .

Although mucoactive drugs (which improve the ease of mucus clearance) may be effective in mucus hypersecretion, the uncertainty surrounding their effectiveness, due primarily to the relative lack of evidence from randomised controlled trials and an uncertainty from epidemiological studies linking mucus hypersecretion with mortality8-11, have led to their poor diffusion and adoption in international guidelines 7. However, in combination with newer therapeutic strategies currently in research and development phase targeting airway inflammation and thus reducing mucus hypersecretion, there is a renewed interest in re-evaluating mucus clearance strategies in improving HRQL, exacerbations and morbidity associated with COPD 12;13.