Airway Bifurcations Research Articles

Periodic flow at airway bifurcations. II. Flow partitioning

The distribution of flow among parallel pathways is believed to be determined by the balance of downstream mechanical loads or time constants. We studied the influence of upstream flow conditions and airway geometry vs. downstream mechanical impedances in determining flow partitioning at airway bifurcations. Each model consisted of a single rigid bifurcation with various branching angles and area ratios but having identical pathway impedances. Sinusoidal volumetric oscillations were applied at the parent duct with various frequencies and tidal volumes. Measuring the terminal pressures continuously, we calculated the flow distribution. When flow amplitude was small, flow partitioning was homogeneous and synchronous, as expected in a system possessing homogeneous pathway impedances and time constants. But when flow amplitude was large and frequency was high, appreciable heterogeneity and asynchrony of flow partitioning arose; during midinspiration the high-velocity flow stream preferentially favored the axial pathway. This effect vanished in the absence of a net area change at the bifurcation. For a given bifurcation geometry, these observations could be organized using only two nondimensional parameters, neither of which incorporated consideration of fluid friction. The description of temporal events required, in addition, a nondimensional time. Therefore these flow-dependent phenomena and their underlying mechanisms differ fundamentally from those described in classical impedance models. The complex pattern of nonuniform interregional behaviors apparent in whole lungs when tidal volume and frequency are large (Allen et al., J. Clin. Invest. 76: 620-629, 1985) is reiterated faithfully in models consisting of only two compartments with homogeneous time constants. As such, the behaviors observed in lungs would appear to be attributable in large part to fluid dynamic factors in central airways.

Periodic flow at airway bifurcations. I. Development of steady pressure differences

In studies of large-amplitude periodic flows at an airway bifurcation, we found an appreciable steady-state pressure difference between the terminal units. To elucidate the fluid dynamic origins of such steady-state pressure differences, we studied single asymmetric bifurcation models with various area ratios and branching angles. The daughter ducts were identical in size and were terminated into identical elastic loads. Sinusoidal flow oscillations were applied at the parent duct so that the upstream Reynolds number ranged from 30 to 77,000 and the Womersley parameter from 2 to 30. The steady-state component (time averaged) of the pressure measured at the terminal with the smaller branching angle was found to be consistently higher than that at the other terminal. This steady-state pressure difference scaled approximately as a fixed fraction of the parent duct dynamic head. Guided by the results of flow-visualization studies, we modeled such behavior based on the temporal and spatial differences of head loss between the two branches of the bifurcation. Our results suggest that interlobar heterogeneity of mean alveolar-pressure observed in excised canine lungs during high frequency oscillation (Allen et al., J. Appl. Physiol. 62: 223-228, 1987) arises solely from fluid dynamic origins: differential head loss due to asymmetry of central airway branching structure.

Periodic flow at airway bifurcations. III. Energy dissipation

We measured the energy dissipation associated with large-amplitude periodic flow through airway bifurcation models. Each model consisted of a single asymmetric bifurcation with a different branching angle and area ratio, with each branch terminated into an identical elastic load. Sinusoidal volumetric oscillations were applied at the parent duct so that the upstream Reynolds number (Re) varied from 30 to 77,000 and the Womersley parameter (alpha) from 4 to 30. Pressures were measured continuously at the parent duct and at both terminals, and instantaneous branch flow rates were calculated. Time-averaged energy dissipation in the bifurcation was computed from an energy budget over a control volume integrated over a cycle and was expressed as a friction factor, F. We found that when tidal volume was small [ratio of tidal volume to resident (dead space) volume, VT/VD less than 1], F was independent of branching angle and fell with increasing alpha and VT/VD. When tidal volume was large (VT/VD greater than 1), F increased with increasing branching angle and varied less strongly with alpha and VT/VD. No simple benchmark flow represented the data well over the entire experimental range. This study demonstrates that only two nondimensional parameters, alpha and VT/VD, are necessary and are sufficient to describe time-averaged energy dissipation in a given bifurcation geometry during sinusoidal flow.

Fiber Deposition in Airway Bifurcations

In previous efforts mathematical models have been developed (Balásházy et al., 1990a, b) to describe behavior of compact particles at airway bifurcations under the simultaneous action of inertial impactional and gravitational deposition mechanisms. Now, we expand the theory for the motion of fibrous particles where another deposition process, interception, may play an important role. Current U.S. EPA health effects concerns include both natural (asbestos) and manufactured (glass) airborne fibers. For the calculation of the deposition efficiency we assume that fibers are either parallel, perpendicular, or randomly oriented to their centers-of-mass trajectories relative to the entraining airflow. Deposition is computed using three different morphological configurations to characterize a bifurcation zone: (i) a single tube bend (Model I); (ii) a straight parent tube attached to two curved daughter tubes (Model II); and, (iii) three straight tubes joined together by two curved tube sections (Model III). A refinement of Model III is proposed to permit more accurate spatial descriptions of localized differential distributions of particle deposition efficiencies. Theoretical predictions are compared to experimental data and other computations presented in the open literature. Our calculated differential distribution patterns within bifurcation zones indicate enhanced deposition, or "hot spots", at carinal ridges. This implies increased exposures to underlying airway cells (relative to neighboring locations) which may be of importance regarding the risk assessment of inhaled fibers.

Inertial Impaction and Gravitational Deposition of Aerosols in Curved Tubes and Airway Bifurcations

A theoretical model of the simultaneous action of inertial impaction and gravitational forces on a particle moving in three dimensional circular bends is presented. Deposition efficiencies are computed for three different idealized flow patterns: 1) uniform; 2) radially dependent, or rotational; and 3) parabolic. The bend is in a vertical plane, the inclusive angle of the bend is a variable, and its inlet can be at any angle of alignment to the horizontal. The results of these new simulations are compared with available experimental data and theoretical computations. The integral and differential distributions of deposition along the length of the tubes are examined. The relative contributions of the inertial impaction and sedimentation mechanisms to total (i.e., simultaneous) deposition are studied. The applicability of simple pipe bend models, and their appropriate limits, are examined for the deposition of aerosols in human tracheobronchial bifurcations. The conceptual model is further developed for th...

A Simplified Model of Interceptional Deposition of Fibers at Airway Bifurcations

Based on a simplified model, a theoretical expression for the deposition efficiency of fibers by interception at the bifurcation of a parent–daughter system was derived. In deriving this expression, the simultaneous effect of the velocity shear of the flow and Brownian rotation on fiber orientation was considered. Calculated deposition efficiencies in different airway generations of a Weibel lung model showed that the results obtained previously by Harris and Frazer in 1976 were valid only for small fibers. More accurate deposition results for large fibers are presented in this paper.

Distribution and frequency of neuro-epithelial bodies in post-natal rabbit lung: Quantitative study with monoclonal antibody against serotonin

The distribution, frequency and size of neuroepithelial bodies (NEB) were studied in lungs of rabbits during different stages of development (27-day fetus, newborn, 6, 11, 21, 28 and 56 days postnatally). NEB were visualized by immunostaining with monoclonal antibody against serotonin. Detailed quantitation of NEB was performed by use of camera lucida drawings of immunostained serial sections from the same anatomical region, i.e. the lower lobe of the left lung. The total number of NEB was counted and expressed per epithelial length of airway, surface area and volume. The size of NEB defined as surface area as well as the position of NEB in relation to the airway bifurcations was assessed in airways of different sizes. The overall number and size of NEB were found to increase during the immediate perinatal period followed by a sharp decline at 56 days of age. The number of NEB peaked at 6 days postnatally (mean 175.5 NEB/mm3 of airway epithelium) and declined significantly (3.0 NEB/mm3) at 56 days of postnatal age. The size of NEB reached its maximum at 11 days (mean surface area 659.54 microns 2, with the largest NEB measuring 1839.98 microns 2). By 56 days of age, NEB became significantly smaller (mean surface area 177.29 microns 2) consisting of small clusters of cells situated deep within the airway epithelium. At all ages, about half of all NEB (mean 47.6%) were localized within the small peripheral airways with up to 63.9% located at airway bifurcations. These findings indicate that the "functional activity" of NEB may be confined predominantly to the perinatal period. The postulated functions of NEB include those of intrapulmonary hypoxia-sensitive chemoreceptors and/or endocrine-paracrine activity in the lung. Such functions(s) may be important during adaptation to extrauterine life as well as for growth and development of the lung.

The Significance of Enhanced Radionuclide Deposition at Bronchial Bifurcations

Experiments have been conducted to quantitate the deposition patterns of monodisperse aerosols in surrogates of the human upper respiratory tract. Laryngeal casts and most upper airway bifurcations were sites of preferential particle deposition. Highly concentrated deposits were detected at carinal ridges within bifurcation zones. Together with impaired mucociliary clearance at branching sites, this initial deposition pattern results in localized accumulations of radionuclides within bifurcation zones.

Asbestos‐induced changes in rat lung parenchyma

Fischer 344 rats have been exposed to UICC crocidolite by whole-body inhalation procedures for periods of 1 d to 12 mo. Material was obtained from the same location in the left lung, and the numbers of cells in the parenchyma were identified and determined by transmission electron microscopy. An immediate increase (1 d of exposure) was evident in the number of type II cells, suggesting a direct action of the dust on these cells. The number of interstitial and alveolar macrophages showed a significant increase after 3 mo of exposure. The number of alveolar macrophages containing dust particles after a 1-d exposure was 49%, and the corresponding value after 12 mo of exposure was 92%. The longer periods of exposure were associated with an increase in the number of particles per macrophage. Polymorphs appeared in the interstitium at airway bifurcations, prior to their appearance in the alveolar space. These bifurcations were also the initial sites where evidence of cell damage and collagen deposition was seen. In this experiment crocidolite appears to be weakly fibrogenic, and other factors may be needed to produce the marked lesions seen in human asbestosis.

Deposition pattern of inorganic particles at the alveolar level in the lungs of rats and mice.

The early pathogenesis of particle-induced lung disease is likely to be determined in large part by the initial pattern of dust deposition at the alveolar level. We have studied the deposition pattern of 5 aerosolized dusts (chrysotile and crocidolite asbestos, fiber glass, alpha-quartz, and ash from Mt. St. Helens) in the lungs of rats. Mice were exposed to chrysotile asbestos. Quantitative electron microscopy was carried out on tissues fixed by vascular perfusion. Immediately after a brief exposure, significantly (p less than or equal to 0.01) greater numbers of particulates had deposited on alveolar duct bifurcations when compared with the number of particles on duct surfaces adjacent to the bifurcations. Few particles were counted at midpoints between bifurcations, and particles rarely were observed within alveoli. Our data show that regardless of mineral nature, shape, or concentration, inhaled particulates small enough to pass through the conducting airways are deposited primarily at alveolar duct bifurcations. We proposed that the alveolar deposition patterns observed are the result of air-flow characteristics that cause enhanced deposition of particles at alveolar duct bifurcations intersecting the flow. This is similar to deposition patterns that occur at bifurcations of conducting airways.

Acoustic modeling of lung dynamics using bond graphs.

Bond graphs are used to model the acoustic behavior of the respiratory system. The model includes the distributed dynamics of the upper airways while the lower passage generations are represented by "lumping" of resistance and compliance effects. The lower airway representation is terminated with ten lung segments. The model is accurate for frequencies as high as 8500 Hz. The model is currently capable of predicting system eigenvalues as a function of system parameters and geometry for a "nonbreathing" lung. Future plans include modifying the model to include lung segment expansion and contraction as well as turbulence generation at airway bifurcations.

Measurement of particle dose distribution in a model of a human larynx and tracheobronchial tree

Abstract Monodisperse ammonium fluorescein aerosols were deposited in combined replica human larynx casts and single-pathway tracheobronchial (TB) models. These new TB models permit control of airflow rates in airways, are constructed following anatomical measurements, and are expendable for quantification of aerosol deposition. Larynx configurations corresponded to steady inspiratory flow rates of 15, 30 and 601/min. Particle sizes ranged from 1.9 to 6.7 μm. Total larynx and TB deposition measurements are expressed in terms of a single parameter, the particle Stokes number. Intratracheobronchial dose distributions indicated large tracheal losses attributed to the laryngeal jet. Some airway bifurcations were sites of enhanced deposition. Such “hot spots” indicate high dosage to human airway cells and have important inhalation toxicology and aerosol therapy implications. Findings are in agreement with aerosol deposition data from replica TB casts and human inhalation exposure tests, which suggest that the single-pathway TB model is suitable for use in studies of factors effecting aerosol behavior and deposition in the human.

Morphological and cytochemical characterization of neuroepithelial bodies in fetal rabbit lung. I. Studies of isolated neuroepithelial bodies.

Neuroepithelial bodies (NEB) in 29-day fetal rabbit lung were examined by light microscopy and cytochemistry to demonstrate their structural and biochemical properties in situ. Longitudinal sections of NEB at airway bifurcations demonstrated their chemoreceptor-like appearance. Furthermore, the cytochemical presence of serotonin, acetylcholinesterase, formaldehyde-induced fluorescence, and silver-staining properties demonstrated the neural-like biochemical properties of NEB cells. Forty-one NEB and eight single neuroendocrine cells from whole fetal lungs were examined ultrastructurally. Juxtaluminal junctional complexes composed of tight and intermediate junctions, desmosomes, and cytoplasmic filaments were demonstrated in the corpuscular-shaped NEB. Basal bodies were apparent in NEB cell cytoplasm; cilia extended from NEB cells. Dense-core vesicles (DCV) were of at least three types: type 1, type 2, and enterochromaffin type. The majority of epithelial cells adjacent to NEB in near-term airway epithelium were undifferentiated, with large amounts of glycogen. However, ciliated cells were adjacent to some small NEB and single neuroendocrine cells; mucus or Clara-type cells were not observed. NEB isolated by collagenase treatment revealed an intact organoid structure, DCV, and desmosomes and retained their argyrophilia and formaldehyde-induced fluorescence. NEB were recovered in cell fractions separated by unit gravity that had cells in clumps of four or more. One to five NEB stained with silver in cytocentrifuge preparations of control, mixed cells, whereas up to 20 intact NEB were demonstrated in the clump-containing, separated fractions. We propose that isolated NEB retain certain biochemical and metabolic properties similar to those of their counterparts in situ. Serotonin and 5-hydroxyindole acetic acid were found by high-performance liquid chromatography analysis in the fractions containing NEB, and amine precursor uptake and decarboxylation (APUD) activity were demonstrated. Moreover, muscarinic cholinergic receptors were detected, consistent with the occurrence of acetylcholinesterase in NEB. The elution profile of bombesin radioimmunoactivity substantiated that isolated fetal rabbit NEB contained this neuropeptide and that NEB were enriched by unit gravity sedimentation. These studies suggest that NEB are structurally and functionally developed before other cell types in immature airway epithelium and can be isolated as intact organoids, which retain some of their structural and metabolic integrity.

Effect of the laryngeal jet on particle deposition in the human trachea and upper bronchial airways

Abstract Preferential sites of particle deposition within the human respiratory system are known to correlate with primary cancer sites, and are therefore important in the etiology of neoplastic respiratory diseases. In this study, we characterized the intrabronchial and intratracheal patterns of deposition in a hollow cast of a human larynx-tracheobronchial tree, and examined the effects of airflow and turbulence on particle deposition by performing airflow measurements in the hollow cast and an “ideal” airway bifurcation model. Experimental results revealed a deposition “hot spot” for particles greater than 2 μm in mass median aerodynamic diameter in the trachea at 2 cm below the larynx. The enhancement of deposition in the trachea was studied by making comparative airflow and detailed morphometry measurements in a hollow lung cast and in an “ideal” model. The larynx had a significant effect on the local flow field in the trachea of the hollow cast and this effect extended to and beyond the tracheal bifurcation. This accounted for some of the difference in flow field at the bifurcation between the cast and an “ideal” model. Additional differences were related to the different shapes of the transitional regions near the bifurcation.

Deposition of particles in model airways.

The deposition of monodisperse aerosols in models of single lung airway bifurcations was studied. The particles, generated by spinning disk, were in the size range of 4.2--8.8 microns (density 1.3 X 10(3) kg . m-3). The model bifurcations were symmetrical, of physiological size, and based on established morphological data. The effects on percentage deposition (P) of flow rate (expressed as Reynolds' number. Re), particle diameter (d), tube diameter (D), and bifurcation angle (2 theta) were studied and a generalized expression for deposition based on these variables was obtained, viz., P = 11.04 X 10(5) Re (d/D)2.5sin3 theta. The applicability of this equation is discussed.

Model for aerosol impaction in the lung airways

A finite-difference model for aerosol impaction at an airway bifurcation has been presented. Results suggest that deposition due to impaction is relatively independent of the bifurcation angle for Stokes numbers less than 0.35. For larger values of Stokes number, impaction increases with increasing angle; asymptotic results are obtained for large angles. From comparison with Landahl's analysis, it is evident that the fluid flow field must be considered in any detailed account of impaction.

Pressure drop and fluid flow regime of air inspired into the human lung.

ARTICLESPressure drop and fluid flow regime of air inspired into the human lungD. E. Olson, G. A. Dart, and G. F. FilleyD. E. Olson, G. A. Dart, and G. F. FilleyPublished Online:01 Apr 1970https://doi.org/10.1152/jappl.1970.28.4.482MoreSectionsPDF (3 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByModeling pressure relationships of inspired air into the human lung bifurcations through simulations19 March 2018 | International Journal for Computational Methods in Engineering Science and Mechanics, Vol. 19, No. 2The Direct Effect of Hyperosmolar Agents on Ciliary Beating of Human Bronchial Epithelial CellsJournal of Aerosol Medicine and Pulmonary Drug Delivery, Vol. 25, No. 2Role of Subglottal Shape in Turbulence Reduction1 March 2009 | Annals of Otology, Rhinology & Laryngology, Vol. 118, No. 3Use of Asthmatic Pulmonary Function Test Data to Predict Lung DepositionJournal of Aerosol Medicine, Vol. 20, No. 2Dose Delivery Late in the Breath Can Increase Dry Powder Aerosol Penetration into the LungsJournal of Aerosol Medicine, Vol. 18, No. 1Airflow structures and nano-particle deposition in a human upper airway modelJournal of Computational Physics, Vol. 198, No. 1Risk assessment dosimetry model for inhaled particulate matter: I. Human subjectsToxicology Letters, Vol. 138, No. 1-2Usefulness of helium???oxygen mixtures in the treatment of mechanically ventilated patientsCurrent Opinion in Critical Care, Vol. 9, No. 1INFLUENCES OF PARAMETER UNCERTAINTIES WITHIN THE ICRP 66 RESPIRATORY TRACT MODELHealth Physics, Vol. 81, No. 4Fluid Dynamics in Airway Bifurcations: I. Primary Flows1 October 2008 | Inhalation Toxicology, Vol. 13, No. 4L'héliox en réanimation et en médecine d'urgenceRéanimation Urgences, Vol. 9, No. 5Respiratory Mechanics during Xenon Anesthesia in PigsAnesthesiology, Vol. 91, No. 5Particle deposition in airway bifurcations—I. Inspiratory flowJournal of Aerosol Science, Vol. 24, No. 6Factors affecting distribution of airflow in a human tracheobronchial castRespiration Physiology, Vol. 93, No. 3Inspiratory particle deposition in airway bifurcation modelsJournal of Aerosol Science, Vol. 22, No. 1Retention Modeling of Diesel Exhaust Particles in Rats and HumansJournal of Aerosol Medicine, Vol. 4, No. 2Fiber Deposition in Airway BifurcationsJournal of Aerosol Medicine, Vol. 3, No. 4Morphometric variability of the human upper bronchial treeRespiration Physiology, Vol. 59, No. 3Comparison of experimental and calculated data for the total and regional deposition in the human lungJournal of Aerosol Science, Vol. 16, No. 2Physiological basis and interpretation of indices of pulmonary mechanics.Environmental Health Perspectives, Vol. 56Sedimentational deposition of 5 μm aerosol particles in the small airways of the human lungJournal of Aerosol Science, Vol. 15, No. 6Mathematical models of particle deposition in the human respiratory tractJournal of Aerosol Science, Vol. 15, No. 6Ventilation inhomogeneity: Alveolar mechanics and gas distributionJournal of Biomechanics, Vol. 16, No. 12Monitoring the state of the human airways by analysis of respiratory soundActa Astronautica, Vol. 6, No. 9Deposition of polydisperse aerosols in two glass models representing the upper human airwaysJournal of Aerosol Science, Vol. 8, No. 6Physiologic basis and interpretation of common indices of respiratory mechanical function.Environmental Health Perspectives, Vol. 16Transient flow characteristics in an idealized bronchial bifurcationRespiration Physiology, Vol. 21, No. 1Expiratory flow rates, driving pressures and time-dependent factors. Simulation by means of a modelRespiration Physiology, Vol. 20, No. 3A non-linear theory of the distribution of pulmonary ventilationRespiration Physiology, Vol. 15, No. 1 More from this issue > Volume 28Issue 4April 1970Pages 482-494 Copyright & PermissionsCopyright © 1970 the American Physiological Societyhttps://doi.org/10.1152/jappl.1970.28.4.482PubMed5437439History Published online 1 April 1970 Published in print 1 April 1970 Metrics