Respiratory muscle activity in patients with COPD walking to exhaustion with and without pressure support

The function of the diaphragm and other respiratory muscles during exercise in chronic obstructive pulmonary disease (COPD) remains controversial and few data exist regarding respiratory muscle pressure generation in this sit uation. The inspiratory pressure/time products of the oesophageal and transdiaphrag matic pressure, and the expiratory gastric pressure/time product during exh austive treadmill walking in 12 patients with severe COPD are reported. The effect of noninvasive positive pressure ventilation during treadmill exerc ise was also examined in a subgroup of patients (n=6). During free walking, the inspiratory pressure/time products rose early in t he walk and then remained level until the patients were forced to stop beca use of intolerable dyspnoea, In contrast, the expiratory gastric pressure/t ime product increased exhaustive progressively throughout the walk. When pa tients walked the same distance assisted by noninvasive positive pressure v entilation, a substantial reduction was observed in the inspiratory and exp iratory pressure/time products throughout the walk. When patients walked wi th positive pressure ventilation for as long as they could, the pressure/ti me products observed at exercise cessation were lower than those observed d uring exercise cessation after free walking. It is concluded that, in severe chronic obstructive pulmonary disease, insp iratory muscle pressure generation does not increase to meet the demands im posed by exhaustive exercise, whereas expiratory muscle pressure generation rises progressively. Inspiratory pressure support was shown to substantial ly unload all components of the respiratory muscle pump.