Fig. 1.

Schematic representation of the physiologic effects of Nasal High Flow (NHF) and possible impact of the flow. Increase in airway pressure and FiO₂ improve oxygenation by different mechanisms and may be optimal at higher flows. Most of dead-space wash-out-related effects (increased CO₂ clearance, decrease respiratory drive, respiratory rate and effort to breathe) may be obtained for lower flows. All these physiological effects probably explain the improved comfort in patients with respiratory failure and possibly the outcomes. NHF nasal high flow, Paw airway pressure; FiO₂ fraction of inspired oxygen, EELV end-expiratory lung volume, RR respiratory rate, V_E minute volume, WOB work of breathing