Tree Geometry Research Articles

Earliest effects of sudden occlusions on pressure profiles in selected locations of the human systemic arterial system.

We have developed a numerical simulation method for predicting the time dependence (wave form) of pressure at any location in the systemic arterial system in humans. The method uses the matlab-Simulink environment. The input data include explicitly the geometry of the arterial tree, treated up to an arbitrary bifurcation level, and the elastic properties of arteries as well as rheological parameters of blood. Thus, the impact of anatomic details of an individual subject can be studied. The method is applied here to reveal the earliest stages of mechanical reaction of the pressure profiles to sudden local blockages (thromboses or embolisms) of selected arteries. The results obtained with a purely passive model provide reference data indispensable for studies of longer-term effects due to neural and humoral mechanisms. The reliability of the results has been checked by comparison of two available sets of anatomic, elastic, and rheological data involving (i) 55 and (ii) 138 arterial segments. The remaining arteries have been replaced with the appropriate resistive elements. Both models are efficient in predicting an overall shift of pressure, whereas the accuracy of the 55-segment model in reproducing the detailed wave forms and stabilization times turns out dependent on the location of the blockage and the observation point.

FROM TLS POINT CLOUDS TO 3D MODELS OF TREES: A COMPARISON OF EXISTING ALGORITHMS FOR 3D TREE RECONSTRUCTION

Abstract. 3D models of tree geometry are important for numerous studies, such as for urban planning or agricultural studies. In climatology, tree models can be necessary for simulating the cooling effect of trees by estimating their evapotranspiration. The literature shows that the more accurate the 3D structure of a tree is, the more accurate microclimate models are. This is the reason why, since 2013, we have been developing an algorithm for the reconstruction of trees from terrestrial laser scanner (TLS) data, which we call TreeArchitecture. Meanwhile, new promising algorithms dedicated to tree reconstruction have emerged in the literature. In this paper, we assess the capacity of our algorithm and of two others -PlantScan3D and SimpleTree- to reconstruct the 3D structure of trees. The aim of this reconstruction is to be able to characterize the geometric complexity of trees, with different heights, sizes and shapes of branches. Based on a specific surveying workflow with a TLS, we have acquired dense point clouds of six different urban trees, with specific architectures, before reconstructing them with each algorithm. Finally, qualitative and quantitative assessments of the models are performed using reference tree reconstructions and field measurements. Based on this assessment, the advantages and the limits of every reconstruction algorithm are highlighted. Anyway, very satisfying results can be reached for 3D reconstructions of tree topology as well as of tree volume.

Mixed Hölder matrix discovery via wavelet shrinkage and Calderón–Zygmund decompositions

This paper concerns two related problems in the analysis of data matrices whose rows and columns are equipped with tree metrics. First is the problem of recovering a matrix that has been corrupted by additive noise. Under the assumption that the clean matrix exhibits a specific regularity condition, known as the mixed Hölder condition, we adapt the well-known Donoho–Johnstone wavelet shrinkage methods from classical nonparametric statistics to obtain estimators that are within a logarithmic factor of the minimax error rate with respect to mean squared error loss. The second part of this paper develops a theory of Besov spaces on products of tree geometries. We show that matrices with small Besov norm can be written as a sum of a mixed Hölder matrix and a matrix with small support. Such decompositions are known as Calderón–Zygmund decompositions and are of general interest in harmonic analysis. The decompositions we establish impose fewer conditions on the function with small support than previous decompositions of this type while maintaining the same guarantees on the mixed Hölder matrix. As such, they are applicable to a greater variety of matrices and should find use in many data organization problems. As part of our analysis, we provide characterizations of the underlying Besov spaces using wavelets and other multiscale difference operators that are analogous to those from the classical Euclidean theory.

Protective properties of the arterial system against peripherally generated waves

An anatomically detailed model consisting of a network of electric transmission lines is developed to simulate propagation of the pulse waves in humans. The simulations show that the real arterial tree geometry, together with the elastic and rheological parameters of particular segments, ensure an efficient protection of vital organs against pulse waves generated at peripheral locations. Because locomotive movements are the most obvious source of such disturbances, additional cyclic perturbations are applied to the model femoral arteries. It is shown that the impact of such peripherally generated pulse waves onto the pressure profiles at the ascending aorta and at other vital locations of the system is surprisingly weak independently of synchronization/desynchronization with the heart action period. This may witness to an intrinsically protective nature of the arterial tree anatomy in addition to its known functionality of the optimal blood supply at possibly low lumen volume. The extent of the protection is also studied in the presence of a complete arterial embolism at the left common carotid artery.

Design of two by three element fractal tree antenna array for WLAN and WiFi applications

For more antenna miniaturization, novel fractal tree geometry designed for 5 iterations using rectangular and triangular patches that allow decrease in the resonance frequency without occupying more space. Impedance Matching can be improved without changing the main beam direction or current distribution to five iterations with branching half angle of 60 degrees. The antenna fed by a Coaxial or probe feed to improve the narrow bandwidth of Fractal Antenna. The proposed antenna achieves a bandwidth of 31.5% for 10 dB return loss, covering the frequency range 2.4–3.6 GHz for WLAN and WiFi applications. The antenna gain of the fractal element is about 3 dBi. Array is designed to increase the gain and radiation energy. Arrays are configured at operating frequency of 2.4 GHz by using six elements to enhance the gain up to 11 dBi. The obtained gain and frequency are suitable for WLAN and WiFi applications.

A model analysis of climate and CO2 controls on tree growth and carbon allocation in a semi-arid woodland

Many studies have failed to show an increase in the radial growth of trees in response to increasing atmospheric CO2 concentration [CO2] despite the expected enhancement of photosynthetic rates and water-use efficiency at high [CO2]. A global light use efficiency model of photosynthesis, coupled with a generic carbon allocation and tree-growth model based on mass balance and tree geometry principles, was used to simulate annual ring-width variations for the gymnosperm Callitris columellaris in the semi-arid Great Western Woodlands, Western Australia, over the past 100 years. Parameter values for the tree-growth model were derived from independent observations except for sapwood specific respiration rate, fine-root turnover time, fine-root specific respiration rate and the ratio of fine-root mass to foliage area (ζ), which were calibrated to the ring-width measurements by approximate Bayesian optimization. This procedure imposed a strong constraint on ζ. Modelled and observed ring-widths showed quantitatively similar, positive responses to total annual photosynthetically active radiation and soil moisture, and similar negative responses to vapour pressure deficit. The model also produced enhanced radial growth in response to increasing [CO2] during recent decades, but the data do not show this. Recalibration in moving 30-year time windows produced temporal shifts in the estimated values of ζ, including an increase by ca 12% since the 1960s, and eliminated the [CO2]-induced increase in radial growth. The potential effect of CO2 on ring-width was thus shown to be small compared to effects of climate variability even in this semi-arid climate. It could be counteracted in the model by a modest allocation shift, as has been observed in field experiments with raised [CO2].

A multiscale model of placental oxygen exchange: The effect of villous tree structure on exchange efficiency

The placenta is critical to fetal health during pregnancy as it supplies oxygen and nutrients to maintain life. It has a complex structure, and alterations to this structure across spatial scales are associated with several pregnancy complications, including intrauterine growth restriction (IUGR). The relationship between placental structure and its efficiency as an oxygen exchanger is not well understood in normal or pathological pregnancies. Here we present a computational framework that predicts oxygen transport in the placenta which accounts for blood and oxygen transport in the space around a placental functional unit (the villous tree). The model includes the well-defined branching structure of the largest villous tree branches, as well as a smoothed representation of the small terminal villi that comprise the placenta's gas exchange interfaces. The model demonstrates that oxygen exchange is sensitive to villous tree geometry, including the villous branch length and volume, which are seen to change in IUGR. This is because, to be an efficient exchanger, the architecture of the villous tree must provide a balance between maximising the surface area available for exchange, and the opposing condition of allowing sufficient maternal blood flow to penetrate into the space surrounding the tree. The model also predicts an optimum oxygen exchange when the branch angle is 24 °, as villous branches and TBs are spread out sufficiently to channel maternal blood flow deep into the placental tissue for oxygen exchange without being shunted directly into the DVs. Without concurrent change in the branch length and angles, the model predicts that the number of branching generations has a small influence on oxygen exchange. The modelling framework is presented in 2D for simplicity but is extendible to 3D or to incorporate the high-resolution imaging data that is currently evolving to better quantify placental structure.

Simulation of carbon allocation and organ growth variability in apple tree by connecting architectural and source-sink models.

Plant growth depends on carbon availability and allocation among organs. QualiTree has been designed to simulate carbon allocation and partitioning in the peach tree (Prunus persica), whereas MappleT is dedicated to the simulation of apple tree (Malus × domestica) architecture. The objective of this study was to couple both models and adapt QualiTree to apple trees to simulate organ growth traits and their within-tree variability. MappleT was used to generate architectures corresponding to the 'Fuji' cultivar, accounting for the variability within and among individuals. These architectures were input into QualiTree to simulate shoot and fruit growth during a growth cycle. We modified QualiTree to account for the observed shoot polymorphism in apple trees, i.e. different classes (long, medium and short) that were characterized by different growth function parameters. Model outputs were compared with observed 3D tree geometries, considering shoot and final fruit size and growth dynamics. The modelling approach connecting MappleT and QualiTree was appropriate to the simulation of growth and architectural characteristics at the tree scale (plant leaf area, shoot number and types, fruit weight at harvest). At the shoot scale, mean fruit weight and its variability within trees was accurately simulated, whereas the model tended to overestimate individual shoot leaf area and underestimate its variability for each shoot type. Varying the parameter related to the intensity of carbon exchange between shoots revealed that behaviour intermediate between shoot autonomy and a common assimilate pool was required to properly simulate within-tree fruit growth variability. Moreover, the model correctly dealt with the crop load effect on organ growth. This study provides understanding of the integration of shoot ontogenetic properties, carbon supply and transport between entities for simulating organ growth in trees. Further improvements regarding the integration of retroaction loops between carbon allocation and the resulting plant architecture are expected to allow multi-year simulations.

TU‐H‐CAMPUS‐IeP2‐04: Efficient Binary Tree Description of High Resolution Breast Models for in Silico Imaging

Purpose:We introduce a new geometric model for Monte Carlo (MC) simulation of breast tomosynthesis and mammography images with very high resolution digital breast phantoms voxelized at resolutions down to 50 microns or less. This fine sampling of the anatomy is required to reproduce the spiculated lesions and microcalcifications visible in clinical mammograms with pixel sizes under 100 microns. Phantoms voxelized at this resolution require such a large amount of computer memory that it might not be possible to execute the simulation in regular computers or in Graphics Processing Units (GPU), limiting the realism that can be achieved in virtual clinical trials.Methods:The standard voxel‐based geometry model used in MC codes is inefficient in terms of memory use, because uniform regions are described with a large number of identical voxels. We have developed a new geometric model based on a binary tree partition of space. The binary tree recursively divides the object in two equal halves, alternating the x, y, and z dimensions, until a uniform volume or a final voxel are found. A top‐down search of the tree structure is used to determine the exact composition of a particular voxel during the ray‐tracing process.Results:The binary tree geometry was implemented in PENELOPE and its GPU‐accelerated version MC‐GPU. An example tomosynthesis scan was simulated using a computational breast phantom voxelized at 50 micron. This phantom was too large to fit in the GPU memory directly, but its binary tree version required 10 times less memory. The time spend searching the binary tree reduced the simulation speed in half approximately.Conclusion:We have introduced a new geometry model for in silico imaging of very high resolution phantoms. The binary tree model increases the computation time but, more importantly, enables the simulation of more detailed phantoms than previously possible.

Estimating Tropical Forest Structure Using a Terrestrial Lidar.

Forest structure comprises numerous quantifiable biometric components and characteristics, which include tree geometry and stand architecture. These structural components are important in the understanding of the past and future trajectories of these biomes. Tropical forests are often considered the most structurally complex and yet least understood of forested ecosystems. New technologies have provided novel avenues for quantifying biometric properties of forested ecosystems, one of which is LIght Detection And Ranging (lidar). This sensor can be deployed on satellite, aircraft, unmanned aerial vehicles, and terrestrial platforms. In this study we examined the efficacy of a terrestrial lidar scanner (TLS) system in a tropical forest to estimate forest structure. Our study was conducted in January 2012 at La Selva, Costa Rica at twenty locations in a predominantly undisturbed forest. At these locations we collected field measured biometric attributes using a variable plot design. We also collected TLS data from the center of each plot. Using this data we developed relative vegetation profiles (RVPs) and calculated a series of parameters including entropy, Fast Fourier Transform (FFT), number of layers and plant area index to develop statistical relationships with field data. We developed statistical models using a series of multiple linear regressions, all of which converged on significant relationships with the strongest relationship being for mean crown depth (r2 = 0.88, p < 0.001, RMSE = 1.04 m). Tree density was found to have the poorest significant relationship (r2 = 0.50, p < 0.01, RMSE = 153.28 n ha-1). We found a significant relationship between basal area and lidar metrics (r2 = 0.75, p < 0.001, RMSE = 3.76 number ha-1). Parameters selected in our models varied, thus indicating the potential relevance of multiple features in canopy profiles and geometry that are related to field-measured structure. Models for biomass estimation included structural canopy variables in addition to height metrics. Our work indicates that vegetation profiles from TLS data can provide useful information on forest structure.

Geometric modeling of a coffee plant for displacements prediction

Coffee plants can present structural problems during semi-mechanized and mechanized harvesting such as excessive defoliation and breaking branches. For this reason, studies of mechanical response of a coffee plant can help the development of more optimized machines. The main objective of this study is the modeling of a coffee plant for its mechanical behavior evaluation by using the Finite Element Analysis. The presented paper includes modeling, numerical simulations and experimental tests from a Coffea arabica L. plants. Firstly, it was necessary to create a coffee tree geometry based on pieces of a real tree using 3D scanning process. The coffee tree geometry together with experimental data provided materials properties of the wood plant which are used for displacements prediction via Finite Element Analysis. In order to validate the methodology, simulated results were compared to a real plant behavior under static load. Results presented consistent values from the three-dimensional modeling of a coffee plant which demonstrated the potentiality for new applications.

Realistic Representation of Trees in an Urban Canopy Model

A single-layer urban canopy model that captures sub-facet heterogeneity and various hydrological processes is further developed to explicitly incorporate trees within the urban canyon. The physical processes associated with trees are shortwave/longwave radiation exchange, including mutual interception and shading by trees and buildings and multiple reflections, sensible heat and latent heat (through transpiration) exchange, and root water uptake. A computationally-efficient geometric approach is applied to the radiation exchanges, requiring a priori knowledge of view factors. These view factors are first obtained from independent Monte Carlo ray-tracing simulations, and subsequently simple relations, which are functions of canyon aspect ratio and tree-crown ratio, are proposed to estimate them. The developed model is evaluated against field observations at two urban sites and one suburban site, showing improved performance for latent heat flux compared to the previous version that only includes ground vegetation. The trees in the urban canopy act to considerably decrease sensible heat flux and increase latent heat flux, and these effects are found to be more significant in the more dense urban site. Sensitivity tests are then performed to examine the effects of tree geometry relative to canyon geometry. The results indicate that the tree-crown size relative to canyon width is the most influential parameter to decrease sensible heat flux and increase latent heat flux, resulting in cooling of the urban area.

Murray's law revisited: Quémada's fluid model and fractal trees

In 1926, Murray proposed the first law for the optimal design of blood vessels. He minimized the power dissipation arising from the trade-off between fluid circulation and blood maintenance. The law, based on a constant fluid viscosity, states that in the optimal configuration the fluid flow rate inside the vessel is proportional to the cube of the vessel radius, implying that wall shear stress is not dependent on the vessel radius. Murray's law has been found to be true in blood macrocirculation, but not in microcirculation. In 2005, Alarc\'on et al took into account the non monotonous dependence of viscosity on vessel radius - F{\aa}hr{\ae}us-Lindqvist effect - due to phase separation effect of blood. They were able to predict correctly the behavior of wall shear stresses in microcirculation. One last crucial step remains however: to account for the dependence of blood viscosity on shear rates. In this work, we investigate how viscosity dependence on shear rate affects Murray's law. We extended Murray's optimal design to the whole range of Qu\'emada's fluids, that models pseudo-plastic fluids such as blood. Our study shows that Murray's original law is not restricted to Newtonian fluids, it is actually universal for all Qu\'emada's fluid as long as there is no phase separation effect. When phase separation effect occurs, then we derive an extended version of Murray's law. Our analyses are very general and apply to most of fluids with shear dependent rheology. Finally, we study how these extended laws affect the optimal geometries of fractal trees to mimic an idealized arterial network.

On the geometry and allometry of big-buttressed trees - a challenge for forest monitoring: new insights from 3D-modeling with terrestrial laser scanning

Abstract: In many old-growth natural and close-to-natural forest types, notably in humid tropical forests, a relatively small number of very tall trees contribute considerably to stand basal area and biomass. Such trees often show distinct buttress roots with irregular non-convex shapes. Buttresses are complex structures in the lowest stem section, where most tree biomass is located. The methods used to assess the diameter of buttressed trees have a large impact on the determination of volume and biomass, as well as on the resulting estimates of the aboveground carbon stock in tropical forests. As the measurement of diameter at breast height (DBH at 1.3 m) is not feasible in such conditions, the diameter above buttress (DAB), where the cylindrical bole of the tree begins, is usually measured and included as an independent variable in biomass models. We conducted a methodological study aimed at determining the volume and biomass of individual buttressed trees belonging to several tropical species by the application of terrestrial laser scanning (TLS). The geometry and allometry of the buttresses, as well as the change with height along the stem in buttress volume and cross-sectional area were analyzed. Our results suggest that the relationship between cross-sectional areas at DAB height (ADAB) and the actual tree basal area measured at 1.3 m height is relatively strong (R² = 0.87) across a range of different species, buttress morphologies and tree dimensions. Furthermore, the change in stem cross-sectional area with tree height was surprisingly similar and smooth. Despite the small number of trees sampled, the methodological approach used in this study provided new insights on the very irregular geometry of buttressed trees. Our results may help improving the volume and biomass models for buttressed trees, that are crucial contributors to carbon stocks in tropical forests.

Example‐Driven Procedural Urban Roads

AbstractSynthesizing and exploring large‐scale realistic urban road networks is beneficial to 3D content creation, traffic animation and urban planning. In this paper, we present an interactive tool that allows untrained users to design roads with complex realistic details and styles. Roads are generated by growing a geometric graph. During a sketching phase, the user specifies the target area and the examples. During a growing phase, two types of growth are effectively applied to generate roads in the target area; example‐based growth uses patches extracted from the source example to generate roads that preserve some interesting structures in the example road networks; procedural‐based growth uses the statistical information of the source example while effectively adapting the roads to the underlying terrain and the already generated roads. User‐specified warping, blending and interpolation operations are used at will to produce new road network designs that are inspired by the examples. Finally, our method computes city blocks, individual parcels and plausible building and tree geometries. We have used our approach to create road networks covering up to 200 and containing over 3500 km of roads.

Impact of geometric uncertainty on hemodynamic simulations using machine learning

Abstract In the cardiovascular system, blood flow rates, blood velocities and blood pressures can be modeled using the Navier–Stokes equations. Inputs to the system are typically uncertain, such as (a) the geometry of the arterial tree, (b) clinically measured blood pressure and viscosity, (c) boundary resistances, among others. Due to a large number of such parameters, efficient quantification of uncertainty in solution fields in this multi-parameter space is challenging. We use an adaptive stochastic collocation method to quantify the impact of uncertainty in geometry in patient-specific models. We develop a novel subdivision method to define the stochastic space of geometries. To accelerate convergence and make the problem tractable, we use a machine learning approach to approximate the simulation-based solution. Towards this, a reduced order model of the Navier–Stokes equations is developed using a segmental resistance analog boundary conditions (ratio of pressure to flow). Using an offline database of pre-computed solutions, we compute a map (rule) from the features to solution fields. We achieve significant speed-up (of a few orders of magnitude) by approximating the simulation-based solution using a machine learning predictor. A bootstrap aggregated decision tree was found to be the best predictor among many candidate regressors (correlation coefficient of training set was 0.94). We demonstrate stochastic space convergence using the adaptive stochastic collocation method, and also show robustness to the choice of geometry parameterization. The sensitivities to geometry obtained using machine learning had a correlation coefficient of 0.92 with the values obtained using finite element simulations. Segments with significant disease in the larger arteries had the highest sensitivities. Terminal segments are more sensitive to dilation and proximal healthy segments are more sensitive to erosion. Sensitivity to geometry is highest when geometric resistance is comparable to net downstream resistance.

Morphological analysis of pressure wave in the arterial tree with stenosis - a modeling approach.

This paper describes the morphological changes in peripheral signals due to arterial diseases with various severity conditions and site of stenosis using modeling approaches, and its effect in the morphological parameters of radial artery. As stenosis induces abrupt change in geometry and elastic properties of arterial tree (constitutes major reflection sites), hybrid model is well suited for studying the changes in shape of the pressure and flow wave transmitted through the stenosis. These morphological changes in wave shape of peripheral signal have significant diagnostic value in both modern and traditional medicine systems. It can be used for the quantitative assessment of the severity of the arterial diseases.

Patient demographics and cardiovascular risk factors differentially influence geometric remodeling of the aorta compared with the peripheral arteries

Detailed knowledge of the dimensions and shape of the main arteries of the body and how they change with age and disease is important for understanding arterial pathophysiology and improving minimally invasive devices to treat arterial diseases. Our goal was to describe and compare geometric remodeling of the aorta and peripheral arteries in the context of patient demographics and cardiovascular risk factors. Three-dimensional reconstructions of computed tomography angiography scans were performed in 122 subjects 5-93 years of age (mean 47 ± 24 years, 64 M/58 F). Best-fit arterial diameters, lengths, and tortuosity for the principle named arteries in the chest, abdomen, pelvis, and upper thigh were measured, and multiple linear regression analysis was performed to examine how these morphologic parameters associate with patient demographics and risk factors. Large elastic arteries increased their diameter, length, and tortuosity with age, whereas muscular arteries primarily became more tortuous. Demographics and risk factors explained >70% of the variation in diameters of the abdominal aorta, paravisceral aorta, and the aortic arch; and >75% of variation in tortuosity from the profunda femoris to the brachiocephalic artery. Male sex, larger body mass index, and hypertension contributed to larger diameters, whereas the presence of diabetes was associated with somewhat-straighter arteries. Overall, the effects of cardiovascular risk factors on geometric remodeling were small compared with those of demographics. The geometry of the vascular tree is greatly affected by aging, demographics, and some risk factors. Elastic and muscular arteries remodel differently, possibly as the result of differences in their microstructure.

Association Between Vascular Anatomy and Posterior Communicating Artery Aneurysms

Hemodynamic stress, conditioned by the geometry and morphology of the vessel trees, plays an important role in the formation of intracranial aneurysms. The aim of this study was to identify image-based location-specific morphologic parameters that are associated with posterior communicating artery (PCoA) aneurysms. Morphologic parameters obtained from computed tomography angiography of 56 patients with PCoA aneurysms and 23 control patients were evaluated with 3D Slicer, an open-source image analysis software, to generate 3-dimensional models of the aneurysms and surrounding vasculature. Segment lengths, diameters, and vessel-to-vessel angles were examined. To control for genetic and clinical risk factors, the unaffected contralateral side of patients with unilateral PCoA aneurysms was used as a control group for internal carotid artery (ICA)-related parameters. A separate control group with visible PCoAs and aneurysms elsewhere was used as a control group for PCoA-related parameters. Internal carotid artery-related parameters were not statistically different between the PCoA aneurysm and control groups. Univariate and multivariate subgroup analysis for patients with visualized PCoAs demonstrated that a larger PCoA diameter was significantly associated with the presence of a PCoA aneurysm (odds ratio = 12.1, 95% confidence interval = 1.3-17.1, P = 0.04) after adjusting for other morphologic parameters. Larger PCoA diameters are associated with the presence of PCoA aneurysms. These parameters may provide objective metrics to assess aneurysm formation and growth risk stratification in high-risk patients.

The Influence of Airway Tree Geometry and Ventilation Frequency on Airflow Distribution.

The human lung is known to be asymmetric and heterogeneous which leads to an inhomogeneous distribution of air. Within the scope of this paper the influence of the upper airway tree geometry on ventilation distribution and the differences between conventional mechanical ventilation (CMV) and high frequency oscillatory ventilation (HFOV) will be analyzed. The comparison is carried out under the assumption of positive pressure ventilation. Thereby, the mechanics of lung tissue is expected to play a minor role. Oscillatory flow is therefore generated numerically at a 3D model geometry of the upper human airways. For large enough frequencies in the range of HFOV (here 7 Hz) the shape of the velocity profiles changes, but this had no measurable influence on the flow distribution. The flow division is rather governed by airway tree geometry, i.e., branch length, curvature, and tortuosity. A convective net transport of fresh air to the distal branches occurs due to the relocation of mass during ins-/expiration driven by secondary flow. However, a mixing by secondary flow plays a minor role as was suggested by the visualization of particle pathlines. The phenomenon of steady streaming is further investigated by calculating the mean flow of one breathing cycle. Streaming was found to contribute only to a minor percentage to the overall mass transport in the upper lung airways.