The main purpose of this study is to learn how patients breathe on portable oxygen concentrators (POCs), and to get feedback from patients using POCs.

This study aims to examine patient oxygenation levels and markers of exertion (e.g. breath rate, heart rate and breath pattern) while using a portable oxygen concentrator, with the aim to understand exercise desaturation in hypoxemic subjects.

Inclusion Criteria:

• Patient is willing to give written informed consent
• Patient can read and comprehend English
• Patient is ≥ 18 years of age
• Patient has moderate to severe hypoxaemia (SpO2 ≤ 92%) at rest
• Patient reports shortness of breath on exertion

Exclusion Criteria:

• Patient has musculoskeletal impairment, or other impairment that may be the limiting factor in 6MWT
• Patient has a history of a psychological illness or condition such as to interfere with the patient's ability to understand the requirements of the study
• Patient has acute coronary syndrome, acute myo- or pericarditis, acute lung embolism, pulmonary infarction, acute uncontrolled heart insufficiency
• Patient shows signs of acute exacerbation of underlying lung condition
• Patient is deemed to be unsuitable for inclusion in the opinion of the researcher, including for the following reasons:
• they do not comprehend English
• they are unable to provide written informed consent
• they are physically unable to comply with the protocol