NEW & NOTEWORTHY High-flow nasal cannula generates positive airway pressure and reduces respiratory rate. Our findings confirm these physiological effects when the mouth is kept closed. An increased resistance to breathing induces a longer expiratory phase, which leads to decreased respiratory rate and minute ventilation, and therefore to a decreased respiratory workload, counterbalancing the increased pressure-time product per liter. These effects are less apparent with the mouth open and are not observed with continuous positive airway pressure.