 In exacerbated Chronic Obstructive Pulmonary Disease COPD patients, there is augmentation of hypoxia and the obstructive ventilatory disorders is more important. This is correlated with an increase in C-reactive Protein CRP and of inflammatory cytokines and oxidative stress. It has been demonstrated that there is an endothelial dysfunction in answer to hypoxia. Since the exacerbated COPD patients are hypoxic in most cases , we suppose they have an endothelial dysfunction during exacerbation. So we think we will find an augmentation of vascular resistances ,shown by a peripheral arterial tone too high. And this, certainly, play a part in physiopathology of the COPD exacerbation. 