Currently LTOT is provided at a constant fixed-flow rate e.g. 2 litres per minute all the time after appropriate assessment. The flow rate is not changed during usual household activities but is increased for walking. A number of studies have investigated the SpO2 of patients on LTOT during the daytime in patients' homes. The results have shown that patients' SpO2 decreases intermittently whilst they are doing activities of daily living such as watching television, putting away the shopping, having a shower or bath and dressing and undressing. This is a problem as it can lead to breathlessness, increased stress on the heart and affect brain function. In order to correct the drop in SpO2 that patients experience during everyday activities, the investigators have developed an oxygen system, which can automatically change the amount of oxygen delivered depending on a patients' oxygen saturations - an auto-titrating oxygen system. In this study, patients on LTOT will be asked to simulate a series of activities of daily living twice: once whilst on their usual fixed-flow oxygen therapy and once on the auto-titrating oxygen system. The activities will be carried out in a hospital setting. During the activities, SpO2 will be recorded continuously. The main outcome of interest from the study will be the SpO2 throughout the study on fixed-flow oxygen and the auto-titrating oxygen system.