Pulmonary rehabilitation 2007: from bench to practice and back.

COPD is a disease that is not confined to the airways and the lungs, but also produces systemic consequences. Muscle weakness is one of these. It is produced by a multitude of factors including deconditioning, systemic inflammation, oxidative stress, nutritional imbalance, reduced anabolic status, systemic corticosteroids, hypoxemia, hypercapnia, electrolyte disturbances, cardiac failure. The most important factors appear to be inactivity and systemic inflammation. Inactivity was shown to be present in patients with COPD from early in the course of the disease on. Systemic inflammation was shown to be predominantly present during COPD exacerbations. IL-6 has the propensity to reduce muscle function in experimental animals. At present there is no evidence of local production of cytokines in the muscle in patients with COPD. Muscle weakness is also important in the clinical course of the disease as it is associated with exercise intolerance, reduced quality of life, enhanced utilization of health care resources and reduced survival. Rehabilitation is the best treatment for muscle weakness and deconditioning in patients with COPD. Indeed, it is the intervention with the largest effect on health status and exercise capacity in these patients. Several factors that may enhance the effects of rehabilitation have been studied. These include: growth hormone/ IGF-I, anabolic steroids, clenbuterol, creatine, anti-cytokine treatment, erythropoietin, oxygen, non-invasive mechanical ventilation and electrical stimulation. Recently, the potential of protease-inhibitors in reversing deconditioning-induced muscle dysfunction was demonstrated. Adjuncts are potentially particularly useful in patients who do not respond to a rehabilitation programme. Analysis of large d-bases demonstrated that about one third of the patients does not respond to rehabilitation. A follow-up study suggests that decline in exercise capacity after a rehabilitation programme is particularly present in these patients and not in the patients with a clear initial response. A better understanding of the factors controlling the response to rehabilitation, may lead to significant advances in this field.