title: Nasal high flow reduces dead space.
abstract: Recent studies show that nasal high flow (NHF) therapy can support ventilation in patients with acute or chronic respiratory disorders. Clearance of dead space has been suggested as being the key mechanism of respiratory support with NHF therapy. The hypothesis of this study was that NHF in a dose-dependent manner can clear dead space of the upper airways from expired air and decrease rebreathing. The randomized crossover study involved 10 volunteers using scintigraphy with81mKrypton (81mKr) gas during a breath-holding maneuver with closed mouth and in 3 nasally breathing tracheotomized patients by volumetric capnography and oximetry through sampling CO2and O2in the trachea and measuring the inspired volume with inductance plethysmography following NHF rates of 15, 30, and 45 l/min. The scintigraphy revealed a decrease in81mKr gas clearance half-time with an increase of NHF in the nasal cavities [Pearson's correlation coefficient cc = -0.55, P < 0.01], the pharynx (cc = -0.41, P < 0.01), and the trachea (cc = -0.51, P < 0.01). Clearance rates in nasal cavities derived from time constants and MRI-measured volumes were 40.6 ± 12.3 (SD), 52.5 ± 17.7, and 72.9 ± 21.3 ml/s during NHF (15, 30, and 45 l/min, respectively). Measurement of inspired gases in the trachea showed an NHF-dependent decrease of inspired CO2that correlated with an increase of inspired O2(cc = -0.77, P < 0.05). NHF clears the upper airways of expired air, which reduces dead space by a decrease of rebreathing making ventilation more efficient. The dead space clearance is flow and time dependent, and it may extend below the soft palate.
  
  
  
  Clearance of expired air in upper airways by nasal high flow (NHF) can be extended below the soft palate and de facto causes a reduction of dead space. Using scintigraphy, the authors found a relationship between NHF, time, and clearance. Direct measurement of CO2and O2in the trachea confirmed a reduction of rebreathing, providing the actual data on inspired gases, and this can be used for the assessment of other forms of respiratory support.
authors.affiliation: Comprehensive Pneumology Center, German Center for Lung Research, Munich, Germany; moeller@helmholtz-muenchen.de.|Institute of Lung Biology and Disease, Helmholtz Zentrum München-German Research Center for Environmental Health, Neuherberg, Germany.
authors.forename: Winfried
authors.identifier: 0000-0003-3072-1346
authors.initials: W
authors.lastname: Möller
authors.affiliation: Fisher & Paykel Healthcare, Auckland, New Zealand.
authors.forename: Sheng
authors.initials: S
authors.lastname: Feng
authors.affiliation: HELIOS Klinik Hagen-Ambrock, Witten-Herdecke University, Hagen, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Domanski
authors.affiliation: HELIOS Klinik Hagen-Ambrock, Witten-Herdecke University, Hagen, Germany.
authors.forename: Karl-Josef
authors.initials: KJ
authors.lastname: Franke
authors.affiliation: Comprehensive Pneumology Center, German Center for Lung Research, Munich, Germany.|Institute of Lung Biology and Disease, Helmholtz Zentrum München-German Research Center for Environmental Health, Neuherberg, Germany.
authors.forename: Gülnaz
authors.initials: G
authors.lastname: Celik
authors.affiliation: Department of Nuclear Medicine, LMU Medical Center Grosshadern, Munich, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Bartenstein
authors.affiliation: Department of Otolaryngology, Head and Neck Surgery, LMU Medical Center Grosshadern, Munich, Germany.
authors.forename: Sven
authors.initials: S
authors.lastname: Becker
authors.affiliation: Department of Nuclear Medicine, Asklepios Fachkliniken München-Gauting, Gauting, Germany; and.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Meyer
authors.affiliation: Comprehensive Pneumology Center, German Center for Lung Research, Munich, Germany.|Institute of Lung Biology and Disease, Helmholtz Zentrum München-German Research Center for Environmental Health, Neuherberg, Germany.
authors.forename: Otmar
authors.initials: O
authors.lastname: Schmid
authors.affiliation: Comprehensive Pneumology Center, German Center for Lung Research, Munich, Germany.|Institute of Lung Biology and Disease, Helmholtz Zentrum München-German Research Center for Environmental Health, Neuherberg, Germany.|University Hospital of the Ludwig Maximilian University, Munich, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Eickelberg
authors.affiliation: Fisher & Paykel Healthcare, Auckland, New Zealand.
authors.forename: Stanislav
authors.initials: S
authors.lastname: Tatkov
authors.affiliation: HELIOS Klinik Hagen-Ambrock, Witten-Herdecke University, Hagen, Germany.
authors.forename: Georg
authors.initials: G
authors.lastname: Nilius
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D018592:Cross-Over Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009296:Nasal Cavity / Q000378:metabolism / Q000502:physiology*; D009297:Nasal Mucosa / Q000378:metabolism; D009666:Nose / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism; D012123:Pulmonary Ventilation / Q000502:physiology; D012119:Respiration; D012126:Respiratory Dead Space / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology; D014132:Trachea / Q000378:metabolism / Q000502:physiology
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen
keywords: Krypton; dead space; nasal high flow; rebreathing; respiratory support; upper airways