Effects of Automated Oxygen Titration Alone or With High Flow Nasal Therapy on Dyspnea and Exercise Tolerance

Inclusion Criteria: One of them * Moderate to severe COPD (forced expiratory volume in 1 second (FEV1) \< 80% predicted and FEV1/forced vital capacity (FVC) ratio \< 0.7) * Chronic interstitial lung disease such as usual interstitial pneumonitis (UIP), non-specific interstitial pneumonitis (NSIP) or hypersensitivity pneumonitis on high-resolution computed tomography * Pulmonary arterial hypertension type 1 or 4, excluding involvement secondary to collagenosis as well as secondary to congenital heart disease, as diagnosed with mean pulmonary artery pressure \> 25 mm Hg at right heart catheterization * Cystic fibrosis, as diagnosed by a positive sweat test (\>60 mmol/L) or having 2 genetic mutations known to cause cystic fibrosis. AND having a 6-minute walking test with significant desaturation defined as a decrease in O2 saturation greater or equal to 5% with O2 saturation at the end of the walking test \< 88% Exclusion Criteria: * Exacerbation of the primary lung disease in the past 8 weeks * Exercise limiting diseases other than the primary lung disease. * Not reaching the target dyspnea score during the walking tests. * Stage 1 pulmonary sarcoidosis * History of syncope on exertion * SpO2 with effort less than 90% despite the use of 6 L of O2 per minute * Cardiac condition deemed unstable or severe (e.g. severe aortic stenosis) * Disabling or severe rheumatological or neurological condition * Participation in a pulmonary rehabilitation program within the last year * Patients with multi-resistant bacteria