Muscle dysfunction associated with chronic obstructive pulmonary disease.

Skeletal-muscle (both respiratory and limb) abnormalities are common and can have profound effects in patients with chronic inflammatory states such as chronic obstructive pulmonary disease (COPD). Causes include direct inflammatory-mediator effects on muscle function, malnutrition, blood-gas abnormalities, compromised oxygen delivery from right-heart dysfunction, electrolyte imbalances, drugs, and comorbid states. In COPD patients, respiratory muscles are overloaded, which leads to increased fatigue potential, especially during exercise, when hyperinflation worsens. Interestingly, overloaded respiratory muscles develop structural changes that help them adapt to these conditions. In contrast, limb (especially lower extremity) muscles in COPD patients are underloaded as a consequence of disuse, and this leads to muscle atrophy. Treatment is aimed at optimizing lung function, nutritional repletion, aerobic exercise training, and (in certain patients) oxygen therapy. Resistive breathing training is more controversial. Lung-volume-reduction surgery may help with the hyperinflation effects and improve gas exchange and respiratory-muscle function in selected patients.