Chronic Obstructive Pulmonary Disease (COPD) patients in Long-Term Home Oxygen Therapy (LTOT) have a reduction in airflow that is not totally reversible. This obstruction may be associated with an abnormal inflammatory response of the lungs as a result of inhalation of toxic particles, particularly to cigarette smoke. Furthermore, COPD patients also present limited symptoms to physical exercise, significant extrapulmonary effects, including weight loss, nutritional abnormalities and skeletal muscle dysfunction. Hyperinflation has been identified as a major cause of dyspnea and is currently believed to be already present in the early stages of the disease, causing limitations in physical capacity. The progressive exertional dyspnea is most associated with impairment to activities of daily living, decreased quality of life and worse prognosis. Traditionally, the severity of COPD is defined by the degree of obstruction, as measured by forced expiratory volume in one second (FEV1) after bronchodilator use (post-BD) and can be classified as mild, moderate, moderately severe and very severe disease. In the group of patients with Advanced Pulmonary Disease (APD), those with partial pressure values of oxygen (PaO2) lower or equal to 55mmHg, or arterial oxygen saturation (SaO2) lower or equal to 88% in ambient air; or those with PaO2 values between 55-60 or SaO2 lower than 90%, with evidence of pulmonary hypertension or polycythemia require LTOT, over 15 hours / day, with evidence of increased survival. The aim of this study is to evaluate the erythrocyte membranes stability in COPD and APD patients in LTOT compared to healthy subjects. It is a cross-sectional, observational study with evaluation of erythrocyte membranes stability among the groups as well as lung function, physical testing, laboratory analysis, oxidative stress and quality of life questionnaires. As red blood cells are the cells responsible for the gas exchange in the lungs and peripheral tissues, and since the patients with COPD and APD have gas exchange impairment compared to the healthy group, it is expected to find a difference in erythrocyte membranes stability and levels of oxidative stress among the groups.