{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,18]],"date-time":"2026-08-18T04:19:10Z","timestamp":1787026750093,"version":"build-2736575974"},"reference-count":35,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,5,29]],"date-time":"2026-05-29T00:00:00Z","timestamp":1780012800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Med."],"abstract":"<jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>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.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>\n                      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 CO\n                      <jats:sub>2<\/jats:sub>\n                      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.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>\n                      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 CO\n                      <jats:sub>2<\/jats:sub>\n                      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.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>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.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.3389\/fmed.2026.1823238","type":"journal-article","created":{"date-parts":[[2026,5,29]],"date-time":"2026-05-29T06:08:25Z","timestamp":1780034905000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":1,"title":["Asymmetry from an asymmetrical cannula interface and nasogastric tube during nasal high flow enhances dead-space clearance: a fluid dynamics study"],"prefix":"10.3389","volume":"13","author":[{"given":"Zane","family":"Goggin","sequence":"first","affiliation":[{"name":"Department of Mechanical Engineering, University of Canterbury","place":["Christchurch, New Zealand"]},{"name":"Fisher & Paykel Healthcare Limited","place":["Auckland, New Zealand"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Natalia","family":"Kabaliuk","sequence":"additional","affiliation":[{"name":"Department of Mechanical Engineering, University of Canterbury","place":["Christchurch, New Zealand"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Stanislav","family":"Tatkov","sequence":"additional","affiliation":[{"name":"Fisher & Paykel Healthcare Limited","place":["Auckland, New 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