Upper Airway Morphology and Physiology During Graded Positive Pressure and Nasal High Flow: An MRI Study

Background: Nasal and oronasal masks are the gold standard when applying non-invasive ventilation in chronic hypercapnic respiratory failure, providing effective pressure support and CO2 clearance. Nasal high flow (NHF) offers a less invasive alternative with modest positive pressure, but its effect on upper airway anatomy remain largely unknown. The positive airway pressure can influence airway calibre, dynamics, and upper airway closure, but the effects of nasal high flow (NHF) on upper airway morphology have not been directly investigated by MRI. Aims: This study investigates the effects of NHF at different flow rates compared to continuous positive airway pressure (CPAP) on upper airway morphology and respiratory physiology in healthy volunteers and patients with COPD. The primary aim is to determine whether graded NHF and CPAP induce measurable, dose-dependent changes in upper airway volume and cross-sectional area assessed by MRI. Methods: After baseline MRI and physiological assessment, each participant will undergo repeated measurements under two respiratory support modalities: NHF at 30 and 60 L/min and CPAP at 4 and 12 cmH₂O. The two modalities will be applied in randomized order, while both graded settings within each modality will be assessed. MRI will be used to assess changes in upper airway morphology. Respiratory physiology will be assessed under each condition by measuring tidal volume, respiratory rate, minute ventilation, inspiratory and expiratory times, transcutaneous CO₂, inspiratory effort, and work of breathing.