In this controlled randomized crossover trial, 10 stable patients with chronic obstructive respiratory disease (COPD) are treated with Nasal High Flow (NHF) therapy during wakefulness. NHF treatment will inevitably result in increased upper airway washout and thus in a slight reduction of PaCO2 of approximately 2 mmHg. For compensation, a small amount of CO2 is added to the inhaled air during this experimental situation, which keeps the patients' PaCO2 stable. This will allow to examine the effects of NHF therapy on respiratory rate, tidal volume and work of breathing, that are not attributable to the CO2 washout effect.
