title: Convective and diffusive gas transport in canine intrapulmonary airways.
abstract: The significance of convective and diffusive gas transport in the respiratory system was assessed from the response of combined inert gas and particle boluses inhaled into the conducting airways. Particles, considered as "nondiffusing gas," served as tracers for convection and two inert gases with widely different diffusive characteristics (He and SF6) as tracers for convection and diffusion. Six-milliliter boluses labeled with monodisperse di-2-ethylhexyl sebacate droplets of 0.86-microns aerodynamic diameter, 2% He, and 2% SF6 were inspired by three anesthetized mechanically ventilated beagle dogs to volumetric lung depths up to 170 ml. Mixing between inspired and residual air caused dispersion of the inspired bolus, which was quantified in terms of the bolus half-width. Dispersion of particles increased with increasing lung depth to which the boluses were inhaled. The increase followed a power law with exponents less than 0.5 (mean 0.39), indicating that the effect of convective mixing per unit volume was reduced with depth. Within the pulmonary dead space, the behavior of the inert gases He and SF6 was similar to that of the particles, suggesting that gas transport was almost solely due to convection. Beyond the dead space, dispersion of He and SF6 increased more rapidly than dispersion of particles, indicating that diffusion became significant. The gas and particle bolus technique offers a suitable approach to differential analysis of gas transport in intrapulmonary airways of lungs.
authors.affiliation: Projekt Inhalation, GSF-Forschungszentrum für Umwelt- und Gesundheit, Neuherberg, Federal Republic of Germany.
authors.forename: H
authors.initials: H
authors.lastname: Schulz
authors.forename: P
authors.initials: P
authors.lastname: Heilmann
authors.forename: A
authors.initials: A
authors.lastname: Hillebrecht
authors.forename: J
authors.initials: J
authors.lastname: Gebhart
authors.forename: M
authors.initials: M
authors.lastname: Meyer
authors.forename: J
authors.initials: J
authors.lastname: Piiper
authors.forename: J
authors.initials: J
authors.lastname: Heyder
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D004285:Dogs; D006371:Helium; D008176:Lung Volume Measurements; D011653:Pulmonary Diffusing Capacity / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012121:Respiration, Artificial; D012126:Respiratory Dead Space / Q000502:physiology; D013459:Sulfur Hexafluoride
chemical_list: D006371:Helium; D013459:Sulfur Hexafluoride