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In favour of respiratory muscle training

Patients with chronic obstructive pulmonary disease (COPD) generally have inspiratory muscle weakness,1-4 which is ascribed primarily to a reduction in the mechanical advantage of the inspiratory muscles due to hyperinflation.5 Hyperinflation increases the requirement for inspiratory muscle work due to its effect upon the elastic component, as well as the inspiratory threshold load imposed by intrinsic positive end expiratory pressure (PEEP).6 In addition, poor aerobic fitness and peripheral muscle abnormalities lead to a rapid lactic acidosis and a greater ventilatory requirement for exercise,7 which also exacerbates hyperinflation.8 It is therefore no surprise that dyspnoea intensity during exercise in COPD patients correlates significantly with the extent of hyperinflation.9"10 Several studies have noted significant decreases in dyspnoea following interventions that reduced the demand for inspiratory muscle work by reducing operational lung volumes, either pharmacologically,'1 surgicall3'12 or using continuous positive airway pressure. 3 These data suggest that modifying the 'demand' side of the respiratory muscles' 'supply and demand' relationship reduces dyspnoea. It is therefore reasonable to suggest that modifying the 'supply' side of the relationship should evoke similar attenuation of dyspnoea, which is indeed the case (see later).