Chronic Obstructive Pulmonary Disease (COPD) and heart failure are notable contributors to poor health outcomes in New Zealand. Admission to hospital for COPD is a common problem and being readmitted soon after is associated with worse health outcomes and increased healthcare costs. When COPD and heart failure worsen, levels of a waste gas in the blood, carbon dioxide, may rise, which can make a patient’s condition deteriorate. High flow nasal cannulae (HFNC) are a way of delivering warm, moist air, and might reduce both hospital readmission rates and carbon dioxide levels. My PhD involves three trials in which HFNC are used, to see if they lower readmission rates in COPD patients, reduce carbon dioxide in COPD patients and reduce carbon dioxide levels in heart failure patients. If they do have a benefit, HFNC may be a simple and easy to use therapy in patients with COPD and heart failure.