COPD and OHS are respiratory conditions that disrupt normal breathing. Positive airway pressure, specifically Non-Invasive Ventilation (NIV), has been shown to improve breathing and reduce symptoms in patients with these conditions. Regular use of NIV can lead to better symptom management, improved quality of life, and reduced use of healthcare resources. The type of mask used for breathing support can greatly affect a patient's comfort and willingness to use it. For conditions like Obstructive Sleep Apnea (OSA), which is a physical blockage of the airway caused by the relaxation of the muscles of the throat, nasal masks are often used because they are comfortable and work well. But for breathing support in the hospital, full face masks are typically used because patients are having significant trouble breathing and tend to breathe through their mouth.

However, it's important to note that we don't yet fully understand the best way to provide breathing support for long-term NIV users, like COPD and OHS patients. The understanding of breathing route is currently only established for OSA. However, conditions like COPD affect the lungs and the overall system used for breathing, which is different from the throat blockage seen in OSA. So, the assumptions we make based on conditions like OSA may not apply to these other conditions. More research is needed to understand this better.

• Participants undergo PSG, lying on their backs while their breathing route is recorded for about 30 minutes.
• The participants are then put on their prescribed airway pressure support with the first randomized mask, and their breathing is recorded again for 30 minutes.
• The mask is switched to the second mask, and the same procedure is repeated.

Participants are then moved to the sleep laboratory for the night where they are provided with beds.

• They continue NIV therapy with the last mask used during the awake test.
• After at least 60 minutes of recording, participants are awakened to switch back to the first mask. They are then allowed to sleep uninterrupted for the rest of the night.

Inclusion Criteria:

• Age over 18 years
• Prescribed nocturnal NIV for COPD or OHS
• Able to complete an overnight sleep study
• Comfortable to sleep on a standard double bed
• Capacity to complete informed consent

Exclusion Criteria:

• Uncontrolled sleep apnea (Apnea-hypopnea index (AHI) over 15 events/hour off personal NIV device data)
• Prescribed IPAP above 25 cmH2O
• Self-reported pregnancy
• Allergic to adhesive of the sensors
• Self-reported cold/flu symptoms