The purpose of this study is to compare pharyngeal FiO2 in day time with nasal normobaric O2 with inhaled FiO2 in the night time with home care ventilator NIV at the same O2 flow.

in a prospective observational study the investigators will register FiO2 in 15 voluntaries COPD patients as following:

• Pharyngeal FiO2 (G5® Philips™ side stream FiO2) with O2 supply through nasal cannula at basal flow (flow needed by patient). In order to compare FiO2s the investigators will measure FiO2 with 150%, 75%, 50% and 25 % of basal Flow
• And FiO2 during nocturnal NIV (pressure support ventilation; Vivo 50®, Bréas™), using facial or nasal masque (Confort Gel® Respironics™). O2 flow will be basal flow.

Inclusion Criteria:

• informed consent

Exclusion Criteria:

• acute on chronic respiratory distress

Patients with chronic obstructive pulmonary disease. With day time oxygenotherapy and nocturnal NIV and O2 supply