We will determine whether oxygen therapy lowers the level of substances in the blood which cause inflammation, which is one of the adverse effects of COPD and whether oxygen improves overall well being and quality of life as well as sleep quality.

Hypothesis: Isolated nocturnal hypoxemia contributes to chronic systemic inflammation in COPD by activating circulating neutrophils.

Inclusion Criteria:

• Adult males or females with a diagnosis of COPD screened for nocturnal desaturation as indicated above.
• Clinical stability defined by absence of treatment change or need for acute care within the last two months.
• Weight stable, within 5%, in the previous three months as measured during office visits.
• Willingness to participate in a clinical study.

Exclusion Criteria:

• Acute illness within the preceding 2 months.
• Patients who received systemic glucocorticoid therapy within the past month.
• Clinical and/or overnight pulse oximetry evidence of obstructive sleep apnea (OSA). The Multivariate Apnea Prediction Questionnaire (MAP) will be given to all patients to assess the likelihood of OSA based on common symptoms of this disorder. While we recognize that this screening instrument was not evaluated specifically in COPD patients, it assesses common signs and symptoms of OSA. This tool has been shown to identify OSA with 95% sensitivity (63). In addition, the ODI 4% will be determined from the overnight pulse oximetry recording. Patients will be excluded if the MAP score is > 0.4 or if the ODI 4% is >15/hour, which is suggestive of the concomitant presence of obstructive sleep apnea.
• Hypercapnia defined as PaCO2 > 50 mmHg on resting arterial blood gas
• Previous diagnosis of erythrocytosis, pulmonary vascular disease, pleural effusions, ischemic heart disease or congestive heart failure.
• No chronic illnesses known to affect the inflammatory response such as infection, collagen vascular disease, liver disease, thyroid disease or diabetes.
• Primary care or pulmonary physician refusal.
• Patient refusal for any reason.
• Lack of capacity to participate in the informed consent process.