Pilot Study of Physiological Effect of High-Flow Nasal Cannula on Respiratory Pattern and Work of Breathing

Patients affected with severe parenchymal pulmonary diseases, such as Chronic Obstructive Pulmonary Disease (COPD ), may experience dyspnea at rest due to increased work of breathing and reduced oxygenation. The delivery of high-flow humidified nasal oxygen (HFNC) has been shown to have a positive-end-expiratory pressure (PEEP) effect and is able to flush out CO2 from the upper airways, reducing dead space ventilation. Furthermore it has been proven to reduce the respiratory rate shortly after its initiation. These multiple actions offer the potential of changing the respiratory pattern and reducing work of breathing, improving the efficiency of breathing. In this short-term, physiological, open, randomized, cross-over pilot study the investigator swill describe the effects of varying settings of high-flow nasal oxygen on respiratory rate, tidal volume, and diaphragmatic work of breathing in patients with severe COPD. The investigators will also describe changes in gas exchange and effects on the subjects' comfort and dyspnea and the breathing responses to varying setting of CPAP in the subject population.