It is a randomised, single-blind trial of the effect of acute oxygen supplementation on cerebral oxygenation during the 30 sec Sit-To-Stand Test (STST) in chronic obstructive pulmonary disease patients, without resting hypoxemia. After an initial clinical assessment, patients preform the 30sec STST under near-infrared spectroscopy, a non invasive technique which assesses cerebral oxygenation at the prefrontal lobe. Measurements are performed twice, under oxygen supplementation or medical air, in a random order, and the patients are be blinded to the treatment (oxygen or medical air) given.

Inclusion Criteria:

1) clinical diagnosis of COPD, based on smoking history of at least 100 cigarettes and post bronchodilation forced expiratory volume (FEV1) to forced vital capacity (FVC) ratio <0.7, and 2) resting arterial oxygen partial pressure >60 mmHg, according to recent (within a week) arterial blood gases assessment.

Exclusion Criteria:

1) recent COPD exacerbation (as indicated by deterioration of respiratory symptoms, hospital admission and/or change in medication within the previous month), 2) history of specific balance problems (i.e., diagnosed neurological or vestibular disorder), 3) spinal surgery, and 4) lower limb musculoskeletal problems (i.e., surgery, injury or pathology at hip, knee, ankle or foot)

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