This is a study designed to measure, characterize and describe changes on pulse-oxymetry values produced as a result of deep breaths in patients with stable chronic hypoxemic respiratory failure.

There is no standard way of measuring rest pulse-oxymetry in terms of depth of respiration. Rest pulse-oxymetry values are used in the clinical setting to make therapeutic decisions regarding the need of supplemental oxygen. The primary goal of this study is to measure the change of pulse-oxymetry values during an experimental protocol of 10 deep breaths during one minute in patients with chronic hypoxemia. 45 patients will be studied in this first phase. In a second phase, secondary goals will be to measure Vd/Vt vent, noninvasive cardiac output and CT densitometry during the same deep breaths protocol in a subset of 13 patients with the grater increase observed in the first phase of study.

Inclusion Criteria:

• Patients with chronic lung disease causing rest hypoxemia, with rest SpO2 values equal or lower than 94% on room air
• Ambulatory patients capable of performing 6 min walking test
• Patients older than 18 years old.

Exclusion Criteria:

• Patients with significant collagen disease causing Raynaud phenomenon.
• Patients with hypothermia lower than 35 degrees Celsius
• Patients with rest SpO2 values equal or lower than 80% on room air
• Patients unable to perform PFTs
• Patients unable to complete 6 min walking test without supp O2.
• Patients unable to perform experimental deep breaths on CT scan