Frontiers in medicine · 2026
Asymmetry from an asymmetrical cannula interface and nasogastric tube during nasal high flow enhances dead-space clearance: a fluid dynamics study.
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Goggin Zane, Kabaliuk Natalia, Tatkov Stanislav
Аннотация
BACKGROUND: During non-invasive respiratory support with nasal high flow (NHF), an asymmetrical interface (AI) featuring nasal prongs of different sizes has been shown to reduce re-breathing and improve gas exchange in hypoxemic and COPD patients. The objective of this study was to investigate the mechanisms of expired gas clearance during NHF in the presence of a nasogastric (NG) tube, which is commonly used post extubation and causes partial upper-airway occlusion.
METHODS: A computational fluid dynamics study was conducted using an averaged adult upper-airway model with breathing patterns representative of both healthy adults and patients with respiratory failure. Gas flow containing an end-tidal CO2 concentration of 5% was numerically simulated using Ansys Fluent (Ansys Inc., USA) during NHF at rates of 20 L/min and 60 L/min. The computational domain included the nasopharynx and the distal portions of commercially available nasal cannula interfaces.
RESULTS: During NHF, the AI splits the flow both inside and outside the prongs, resulting in differential pressure across the nasal cavities. At an NHF rate of 60 L/min this generated reverse flow through the choanae and increased gas clearance by more than 65%, with up to 91% of expired CO2 expelled through the less occluded naris, compared with a symmetrical cannula interface with similarly-sized nasal prongs. The position of the NG tube on the side of either the large or small prong had only a marginal effect on the almost complete clearance (100% vs. 98.6%) observed at an NHF rate of 60 L/min. However, at a lower NHF rate of 20 L/min, clearance increased from 29.6% to 53.1% when the NG tube was positioned on the side of the large prong.
CONCLUSION: In the computational experiments, asymmetry in the upper-airway cross-sectional area produced by differences in nasal prong size and the presence of an NG tube during NHF alters the gas kinetics and may accelerate anatomical dead-space clearance, thereby reducing re-breathing of expired gas.
METHODS: A computational fluid dynamics study was conducted using an averaged adult upper-airway model with breathing patterns representative of both healthy adults and patients with respiratory failure. Gas flow containing an end-tidal CO2 concentration of 5% was numerically simulated using Ansys Fluent (Ansys Inc., USA) during NHF at rates of 20 L/min and 60 L/min. The computational domain included the nasopharynx and the distal portions of commercially available nasal cannula interfaces.
RESULTS: During NHF, the AI splits the flow both inside and outside the prongs, resulting in differential pressure across the nasal cavities. At an NHF rate of 60 L/min this generated reverse flow through the choanae and increased gas clearance by more than 65%, with up to 91% of expired CO2 expelled through the less occluded naris, compared with a symmetrical cannula interface with similarly-sized nasal prongs. The position of the NG tube on the side of either the large or small prong had only a marginal effect on the almost complete clearance (100% vs. 98.6%) observed at an NHF rate of 60 L/min. However, at a lower NHF rate of 20 L/min, clearance increased from 29.6% to 53.1% when the NG tube was positioned on the side of the large prong.
CONCLUSION: In the computational experiments, asymmetry in the upper-airway cross-sectional area produced by differences in nasal prong size and the presence of an NG tube during NHF alters the gas kinetics and may accelerate anatomical dead-space clearance, thereby reducing re-breathing of expired gas.