It is the best portable oxygen concentrator in its class with Zen-O's pulse and continuous oxygen delivery modes for active patients who need oxygen therapy. Zen-O features respiratory sensing accuracy and therapy response rate (RRT) that automatically adapts to the patient's needs. Zen-O portable oxygen concentrator supplies the patient with up to 2 liters of oxygen per minute according to their needs. Unlike other devices that supply a fixed amount of oxygen, Zen-O automatically increases the amount of oxygen delivered if the patient's respiratory rate increases. "Used for only two weeks, clean and new with all its accessories" The current offer is 3500