An ‘oxygen concentrator’ is a device that draws in outside air and purifies it for people with medical conditions that require oxygen therapy. These conditions include respiratory diseases that prevent the lungs from absorbing enough oxygen, such as chronic obstructive pulmonary disease (COPD) and asthma, as well as other conditions that affect breathing like sleep apnea and cystic fibrosis. Oxygen concentrators require a doctor’s prescription, and cannot be purchased over the counter. Oxygen concentrators are an indispensable sleep aid for many people with breathing conditions because they deliver purified air throughout the night. This guide will look at portable oxygen concentrator designs and functions, as well as the top-rated concentrator models according to owners.