Patients with severe respiratory diseases such as chronic obstructive pulmonary disease (COPD) or obesity-hypoventilation syndrome (OHS) can benefit from having non-invasive ventilation (NIV). Non-invasive ventilation consists of a machine (ventilator) that is blowing air through a mask. NIV provides patients with a bigger expansion of their lung when they are breathing. This better expansion helps patients to have more oxygen and less waste gas (or carbon dioxide) in their body.