The role of inspiratory muscle function and training in the genesis of dyspnoea in asthma and COPD.

The cardinal symptom of both asthma and COPD is dyspnoea, and from a patient perspective, the most troublesome. There are a multitude of inputs to the sensation of dyspnoea, few of which are readily modifiable. The level of inspiratory muscle work contributes to the sense of respiratory muscle effort and thence dyspnoea. Inspiratory muscle work is elevated in patients with COPD and asthma due to hyperinflation and an increased ventilatory requirement for exercise. Treatment tends to concentrate on reducing the load upon the inspiratory muscles induced by hyperinflation. Bronchodilators are the mainstay of treatment for COPD and asthma; they reduce hyperinflation, inspiratory muscle loading and dyspnoea. In addition, programmes of pulmonary rehabilitation have an excellent evidence base for improving dyspnoea, exercise tolerance and quality of life. However, provision within the NHS is limited and not all patients are suitable. One component of pulmonary rehabilitation that can be implemented safely in a home-based setting is specific inspiratory muscle training (IMT). There is a strong theoretical rationale for IMT in patients with airway obstruction, which is also supported by empirical evidence. IMT offers a relatively accessible non-pharmacological treatment for dyspnoea that also improves exercise tolerance and quality of life.