MOBoxy: MoblO2 to Maintain Oxygenation

This is a two-center (National Jewish Health and Stanford University), three-week, unblinded (to O2 delivery), cross-over trial of the MoblO2 device in patients with COPD or ILD who do not require O2 at rest but have been prescribed O2 for use with activity. Once enrolled, each subject will be given an activity monitor and wear it for one week while using their own O2 device as they normally would. After week one, they will continue to wear the activity monitor and be provided a home-fill, stationary O2 concentrator and two D tanks (cylinders) that they will fill from the concentrator. The MoblO2 device will be attached to one D tank, and the other will be in reserve for if/when the first tank runs out, in which case, the MoblO2 device will be removed from the empty tank, attached to the reserve tank for use, and the first tank will be filled from the concentrator and left in reserve. For the next two weeks, whenever patients exert, they will be asked to use the D tanks with the MoblO2 system supplied by the study. During one of the weeks (Week A), the MoblO2 device will be in place atop the D cylinder and will collect data but not control O2 flow. For the other week (Week B), the MoblO2 device will be in place atop the D cylinder and will collect data and control O2 flow. III.B.1. Screening to establish O2 flow: Consented patients will be screened for O2 needs via an O2 titration protocol as follows: patients will be instructed to walk as fast as possible (without running or jogging) back and forth on a 30-meter course in quiet, low-traffic hallway while their SpO2 is monitored. The walk continues until 3 minutes are completed or SpO2 falls to ≤ 88%. If SpO2 does not fall to ≤ 88% by 3 minutes, the patient does not qualify for the study. If SpO2 falls to ≤ 88% before 3 minutes, the walk is halted, and the patient rests for 5 minutes. O2 is then added in 2L/min increments - continuous flow O2, delivered via an E tank on a trolley that the patient pulls while walking - until the patient is able to complete 3 minutes without the SpO2 falling to ≤ 88% for 15 seconds or more. Five-minute rest periods will be ensured between all walks. Patients who need \> 15 L/min O2 will be excluded. Because patients may exert to degrees greater than they did during the screening walks, for the week of the study that the MoblO2 device is in control mode the flow set on the device will be the higher of the following: 1) the flow determined by the screening protocol or 2) the highest flow that a patient has used in the last week. III.B.2. Randomization: Which of the two weeks (A or B) the MoblO2 device will control O2 flow will be randomly assigned via a random number generator; thus, subjects could be randomized to either order: AB or BA. Each of the two sites will randomly assign the order. Patient subjects will have previously-diagnosed COPD or chronic ILD and will have been prescribed by their treating practitioner O2 for use with exertion (but not at rest) for at least one month prior to enrollment. In total, 48 subjects will be recruited: 24 from National Jewish Health and 24 from Stanford University. At each site, 12 subjects will have COPD, and 12 subjects will have ILD. The study will include a number of assessment tools, including actigraphy and patient-reported outcome measures. The Actigraph used is the GT3X + Tri-Axis Actigraphy Monitor (Actigraph LLC; Pensacola, FL) worn on the waist using the provided manufacturer's bands. Subjects will be asked to wear the Actigraph during waking hours, except when bathing or showering. Subjects will receive a charger, and they will be asked to charge the device overnight. Actigraph proprietary software will be used to generate values for sedentary time and time spent in moderately vigorous physical activity. All questionnaires will be administered in electronic format via REDcap and in the same order at each visit. For subjects with COPD, the order will be: CAT, O2 satisfaction survey, FSS, IPAQ, Proactive, PGI-Dyspnea, PGI-Cough, PGI-Energy, and PGI-QOL. For subjects with ILD, the order will be: L-PF, O2 satisfaction survey, FSS, IPAQ, Proactive, PGI-Dyspnea, PGI-Cough, PGI-Energy, and PGI-QOL. Outcome analyses. The initial analyses will compare the MoblO2 controlling O2 flow vs. not. In other analyses, the investigators will compare the MoblO2 controlling O2 flow vs. baseline. The following outcomes will be analyzed using a generalized linear model, with the difference in outcome of interest as the dependent variable: * Activity outcomes (time spent in moderately vigorous physical activity or sedentary time) * Oxygen outcomes (total liters used, MoblO2 over-rides (per hour) * Saturation outcomes (% time with SpO2 \< 90%, % time with SpO2 \< 88%, number of desaturation events \< 88% per hour) * Questionnaire outcomes (CAT score, L-PF scores (Symptoms Module, Dyspnea domain, Cough domain, Energy domain, Impacts Module, L-PF total), IPAQ, Proactive, FSS and PGI) * Oxygen satisfaction survey