title: An Experimental and Numerical Investigation of CO2 Distribution in the Upper Airways During Nasal High Flow Therapy.
abstract: Nasal high flow (NHF) therapy is used to treat a variety of respiratory disorders to improve patient oxygenation. A CO2 washout mechanism is believed to be responsible for the observed increase in oxygenation. In this study, experimentally validated Computational Fluid Dynamics simulations of the CO2 concentration within the upper airway during unassisted and NHF assisted breathing were undertaken with the aim of exploring the existence of this washout mechanism. An anatomically accurate nasal cavity model was generated from a CT scan and breathing was reproduced using a Fourier decomposition of a physiologically measured breath waveform. Time dependent CO2 profiles were obtained at the entrance of the trachea in the experimental model, and were used as simulation boundary conditions. Flow recirculation features were observed in the anterior portion of the nasal cavity upon application of the therapy. This causes the CO2 rich gas to vent from the nostrils reducing the CO2 concentration in the dead space and lowering the inspired CO2 volume. Increasing therapy flow rate increases the penetration depth within the nasal cavity of the low CO2 concentration gas. A 65% decrease in inspired CO2 was observed for therapy flow rates ranging from 0 to 60 L min(-1) supporting the washout mechanism theory.
authors.affiliation: Department of Engineering Science, University of Auckland, Auckland, 1142, New Zealand.
authors.forename: S C
authors.initials: SC
authors.lastname: Van Hove
authors.affiliation: Department of Engineering Science, University of Auckland, Auckland, 1142, New Zealand.
authors.forename: J
authors.initials: J
authors.lastname: Storey
authors.affiliation: Department of Mechanical Engineering, University of Canterbury, Christchurch, 8041, New Zealand.
authors.forename: C
authors.initials: C
authors.lastname: Adams
authors.affiliation: Department of Mechanical Engineering, University of Canterbury, Christchurch, 8041, New Zealand.
authors.forename: K
authors.initials: K
authors.lastname: Dey
authors.affiliation: Department of Mechanical Engineering, University of Canterbury, Christchurch, 8041, New Zealand.
authors.forename: P H
authors.initials: PH
authors.lastname: Geoghegan
authors.affiliation: Department of Mechanical Engineering, University of Canterbury, Christchurch, 8041, New Zealand.
authors.forename: N
authors.initials: N
authors.lastname: Kabaliuk
authors.affiliation: Fisher and Paykel Healthcare Limited, 15 Maurice Paykel Place, Auckland, 2013, New Zealand.
authors.forename: S D
authors.initials: SD
authors.lastname: Oldfield
authors.affiliation: Fisher and Paykel Healthcare Limited, 15 Maurice Paykel Place, Auckland, 2013, New Zealand.
authors.forename: C J T
authors.initials: CJT
authors.lastname: Spence
authors.affiliation: Department of Mechanical Engineering, University of Canterbury, Christchurch, 8041, New Zealand.
authors.forename: M C
authors.initials: MC
authors.lastname: Jermy
authors.affiliation: Department of Engineering Science, University of Auckland, Auckland, 1142, New Zealand.|Auckland Bioengineering Institute, University of Auckland, Auckland, 1142, New Zealand.
authors.forename: V
authors.initials: V
authors.lastname: Suresh
authors.affiliation: Department of Engineering Science, University of Auckland, Auckland, 1142, New Zealand. j.cater@auckland.ac.nz.
authors.forename: J E
authors.initials: JE
authors.lastname: Cater
mesh_terms: D000328:Adult; D002245:Carbon Dioxide / Q000378:metabolism*; D006801:Humans; D006931:Hyperbaric Oxygenation; D008297:Male; D008954:Models, Biological; D009296:Nasal Cavity / Q000378:metabolism* / Q000503:physiopathology; D014132:Trachea / Q000378:metabolism* / Q000503:physiopathology
chemical_list: D002245:Carbon Dioxide
keywords: Breathing therapy; CO2 washout; Computational fluid dynamics; Nasal cavity; Non-invasive ventilation