Airspace Volume Research Articles

C2-O-04Gliding machinery ofMycoplasma mobile,pathogenic bacterium

Wetland plants, such as rice, develop aerenchyma, which is formed due to cell collapse, in their roots as pathways for diffusion of oxygen. Understanding of aerenchyma development in their plants is essential to elucidate the resistance mechanism of these plants to waterlogging stress. Synchrotron X-ray micro-computed tomography (micro-CT) is powerful for in-situ three-dimensional visualization of aerenchyma [1]. In this study, we have employed refraction contrast X-ray micro-CT was performed at a bending magnet beamline BL20B2 of SPring-8 to observe when and where aerenchyma starts to form and how they expand. Imbibed rice (Oryza sativa L. ssp. japonica cv. Nipponbare) caryopses were placed and roots were grown in darkness for 2 to 4 days in plastic tubes filled with agar containing Hoagland medium. The effective pixel size of the detector was 2.33 or 4.86 μm/pixel. Dark areas in a tomographic slice of a root were confirmed to correspond to air spaces formed due to cell collapse. Frequency distribution of location of collapsed cells showed it was the highest in the 5th and the 6th tiers from the outside of the endodermis. Air spaces formed due to collapse of a single cell were frequently observed, indicating that aerenchyma initiates at independent locations and then expand. Frequency of location of an adjacent collapsed cell to an existing collapsed cell tended to be higher in the radial and longitudinal direction. Volume of air space including aerenchyma, which were estimated from isosurface models created using tomograms, was confirmed to increase over a period of time. [1] I Karahara et al, Ann Bot 110 (2012) 503-509. C2-O-04 doi:10.1093/jmicro/dfv186

C2-O-05Non-destructive observation of aerenchyma development in the primary root of rice using X-ray micro-CT

Wetland plants, such as rice, develop aerenchyma, which is formed due to cell collapse, in their roots as pathways for diffusion of oxygen. Understanding of aerenchyma development in their plants is essential to elucidate the resistance mechanism of these plants to waterlogging stress. Synchrotron X-ray micro-computed tomography (micro-CT) is powerful for in-situ three-dimensional visualization of aerenchyma [1]. In this study, we have employed refraction contrast X-ray micro-CT was performed at a bending magnet beamline BL20B2 of SPring-8 to observe when and where aerenchyma starts to form and how they expand. Imbibed rice (Oryza sativa L. ssp. japonica cv. Nipponbare) caryopses were placed and roots were grown in darkness for 2 to 4 days in plastic tubes filled with agar containing Hoagland medium. The effective pixel size of the detector was 2.33 or 4.86 μm/pixel. Dark areas in a tomographic slice of a root were confirmed to correspond to air spaces formed due to cell collapse. Frequency distribution of location of collapsed cells showed it was the highest in the 5th and the 6th tiers from the outside of the endodermis. Air spaces formed due to collapse of a single cell were frequently observed, indicating that aerenchyma initiates at independent locations and then expand. Frequency of location of an adjacent collapsed cell to an existing collapsed cell tended to be higher in the radial and longitudinal direction. Volume of air space including aerenchyma, which were estimated from isosurface models created using tomograms, was confirmed to increase over a period of time. [1] I Karahara et al, Ann Bot 110 (2012) 503-509. C2-O-04 doi:10.1093/jmicro/dfv186

Sugar and phenol content in apple with or without watercore.

Watercore is a physiological disorder affecting fruit of some apple (Malus domestica Borkh.) cultivars. Intercellular spaces are filled with fluid, which reduces intercellular air space volume. In this study individual phenolic content, sugars and organic acids in watercore affected flesh have been identified and quantified. Peroxidase activity was also measured, as a potential stress indicator. The study was performed on three cultivars prone to watercore development 'Delicious', 'Gloster' and 'Fuji'. Total phenolic content was higher in flesh of fruit without watercore in all three cultivars, which was mainly due to higher individual and total flavanol content. In contrast, total and individual dihydrochalcone content was higher in watercore flesh, where it was up to 2.4 times higher from the flesh of fruit without watercore. Also, peroxidase activity was higher in watercore flesh. Higher peroxidase activity and total and individual dihydrochalcone content leads us to believe that oxidative stress occurred. These results show that watercore has an influence on apple fruit sugar and phenol content even before any visual signs of internal breakdown and browning. With the development of non-destructive techniques for phenol content determination, the knowledge about phenolic changes in watercore affected fruits could aid with apple fruit sorting. © 2015 Society of Chemical Industry.

Using magnetic resonance imaging to quantify the inflammatory response following allergen challenge in allergic rhinitis.

Current rhinometric and flow assessments measure nasal patency and are often poorly correlated with rhinitis symptoms. To evaluate magnetic resonance imaging (MRI) as a new method to measure inflammatory changes in nasal and sinus mucosa following nasal allergen challenge. A pilot study (n = 6) determined the optimal technical settings for MRI to measure inflammatory change which were then adopted for the main study. This study was a single blind, placebo-controlled, three-way crossover trial in 14 subjects with seasonal allergic rhinitis. Effects of cetirizine, cetirizine and pseudoephedrine (Cet+PE), or placebo on total nasal symptom scores (TNSS), peak nasal inspiratory flow (PNIF), nasal nitric oxide (nNO), acoustic rhinometry, and MRI end points following nasal intranasal allergen challenge were measured. There were significant changes in all parameters after allergen challenge (P < 0.01), except for nNO. MRI end points were less variable and more consistent than PNIF and acoustic rhinometry in detecting changes after allergen challenge. Total nasal airspace volume was the most sensitive and reproducible MRI measurement, with a mean reduction from -5.37 cm(3) (95%CI -7.35, -3.38; P < 0.001), which was maximal 60 min after allergen challenge. A change of one in TNSS corresponded to a change in MRI volume of -0.57 cm(3). There was an improvement in all parameters (except nNO) in subjects taking Cet+PE compared with placebo, however this did not achieve significance probably because of the small study size (overall analysis P > 0.07; comparison of active versus placebo P > 0.09). MRI provides novel insights into the anatomical inflammatory changes post allergen challenge and provides a new method for assessment of nasal patency and objective measurement of inflammatory responses.

Mesenchymal stem cell-based HSP70 promoter-driven VEGFA induction by resveratrol alleviates elastase-induced emphysema in a mouse model.

Chronic obstructive pulmonary disease (COPD) is a sustained blockage of the airways due to lung inflammation occurring with chronic bronchitis and/or emphysema. Progression of emphysema may be slowed by vascular endothelial growth factor A (VEGFA), which reduces apoptotic tissue depletion. Previously, authors of the present report demonstrated that cis-resveratrol (c-RSV)-induced heat-shock protein 70 (HSP70) promoter-regulated VEGFA expression promoted neovascularization of genetically modified mesenchymal stem cells (HSP-VEGFA-MSC) in a mouse model of ischemic disease. Here, this same stem cell line was evaluated for its protective capacity to alleviate elastase-induced pulmonary emphysema in mice. Results of this study showed that c-RSV-treatment of HSP-VEGFA-MSC exhibited synergy between HSP70 transcription activity and induced expression of anti-oxidant-related genes when challenged by cigarette smoke extracts. Eight weeks after jugular vein injection of HSP-VEGFA-MSC into mice with elastase-induced pulmonary emphysema followed by c-RSV treatment to induce transgene expression, significant improvement was observed in respiratory functions. Expression of VEGFA, endogenous nuclear factor erythroid 2-related factor (Nrf 2), and manganese superoxide dismutase (MnSOD) was significantly increased in the lung tissues of the c-RSV-treated mice. Histopathologic examination of treated mice revealed gradual but significant abatement of emphysema and restoration of airspace volume. In conclusion, the present investigation demonstrates that c-RSV-regulated VEGFA expression in HSP-VEGFA-MSC significantly improved the therapeutic effects on the treatment of COPD in the mouse, possibly avoiding side effects associated with constitutive VEGFA expression.

Lung volume changes after adjuvant breast cancer radiotherapy

Purpose: There is no data for lung volume changes after adjuvant breast cancer radiotherapy. Lung volume at rest and airspace volume increase with aging1. The study aim is to prospectively evaluate lung volume changes for patients who received adjuvant radiotherapy to the breast or chest wall area.

A direction-selective local-thresholding method, DSLT, in combination with a dye-based method for automated three-dimensional segmentation of cells and airspaces in developing leaves.

Quantifying the anatomical data acquired from three-dimensional (3D) images has become increasingly important in recent years. Visualization and image segmentation are essential for acquiring accurate and detailed anatomical data from images; however, plant tissues such as leaves are difficult to image by confocal or multi-photon laser scanning microscopy because their airspaces generate optical aberrations. To overcome this problem, we established a staining method based on Nile Red in silicone-oil solution. Our staining method enables color differentiation between lipid bilayer membranes and airspaces, while minimizing any damage to leaf development. By repeated applications of our staining method we performed time-lapse imaging of a leaf over 5 days. To counteract the drastic decline in signal-to-noise ratio at greater tissue depths, we also developed a local thresholding method (direction-selective local thresholding, DSLT) and an automated iterative segmentation algorithm. The segmentation algorithm uses the DSLT to extract the anatomical structures. Using the proposed methods, we accurately segmented 3D images of intact leaves to single-cell resolution, and measured the airspace volumes in intact leaves.

Real-Time Trajectory Optimisation Models for Next Generation Air Traffic Management Systems

This paper presents models and algorithms for real-time 4-Dimensional Flight Trajectory (4DT) operations in the next generation Communications, Navigation, Surveillance/Air Traffic Management (CNS/ATM) systems. In particular, the models are employed for multi-objective optimisation of 4DT intents in ground-based 4DT Planning, Negotiation and Validation (4-PNV) systems and in airborne Next Generation Flight Management Systems (NG-FMS). The assumed timeframe convention for offline and online air traffic operations is introduced and discussed. The adopted formulation of the multi-objective 4DT optimisation problem includes a number of environmental objectives and operational constraints. In particular, the paper describes a real-time multi-objective optimisation algorithm and the generalised expression of cost function adopted for penalties associated with specific airspace volumes, accounting for weather models, condensation trails models and noise models.

Efficient estimation of the total number of acini in adult rat lung.

Pulmonary airways are subdivided into conducting and gas‐exchanging airways. An acinus is defined as the small tree of gas‐exchanging airways, which is fed by the most distal purely conducting airway. Until now a dissector of five consecutive sections or airway casts were used to count acini. We developed a faster method to estimate the number of acini in young adult rats. Right middle lung lobes were critical point dried or paraffin embedded after heavy metal staining and imaged by X‐ray micro‐CT or synchrotron radiation‐based X‐rays tomographic microscopy. The entrances of the acini were counted in three‐dimensional (3D) stacks of images by scrolling through them and using morphological criteria (airway wall thickness and appearance of alveoli). Segmentation stopper were placed at the acinar entrances for 3D visualizations of the conducting airways. We observed that acinar airways start at various generations and that one transitional bronchiole may serve more than one acinus. A mean of 5612 (±547) acini per lung and a mean airspace volume of 0.907 (±0.108) μL per acinus were estimated. In 60‐day‐old rats neither the number of acini nor the mean acinar volume did correlate with the body weight or the lung volume.

Exploring variation in leaf mass per area (LMA) from leaf to cell: An anatomical analysis of 26 woody species

Plant species differ widely in the leaf biomass invested per unit area (LMA). LMA can be explained by variation in leaf thickness and/or density, both of which are influenced by anatomical tissue composition. The aim of this study is to quantify the anatomical characteristics that underlie variation in LMA in a range of woody species. • Twenty-six woody species, forming 13 species pairs with a deciduous and evergreen species from the same genus or family, were grown in a glasshouse. The youngest full-grown leaves were analyzed for LMA and morpho-anatomical characteristics at leaf, tissue, and cell level. • Considered over all species studied, leaf thickness and density were equally important to explain the variation in LMA, but the class difference between deciduous and evergreen species was mainly determined by thickness, whereas variation within each group was largely due to density. Evergreens had thicker leaves, predominantly caused by a larger volume of mesophyll and air spaces, whereas the higher leaf density within each group was due to a lower proportion of epidermis and air spaces, and overall smaller cells. • The anatomical basis for variation in LMA in woody species depends on the contrast made. Higher LMA in evergreens is mainly due to a greater leaf thickness, caused by a larger volume of mesophyll and air spaces. Within deciduous species and evergreens, higher LMA is caused by a higher density, due to higher volumetric fractions of mesophyll and lower fractions of air spaces and epidermis.

The effect of geniglossal advancement on airway flow using a computational flow dynamics model

Obstructive sleep apnea (OSA) is a sleep disorder caused by partial or complete collapse of the pharyngeal airway. Genioglossal advancement (GGA) is a well-tolerated surgical procedure intended to address hypopharyngeal collapse, yet there are few studies that monitor changes in airflow dynamics at this site. Computation fluid dynamics (CFD) utilizes airflow simulation to predict changes in airflow after anatomic manipulation. We investigated the change in volume and airflow dynamics of the pharyngeal airway after GGA in a cadaveric model. We performed serial GGA from 1 mm (control) to 3, 7, and 9 mm on a lightly preserved cadaver. After each intervention, we performed high-resolution computed tomography scans, reconstructed the pharyngeal airway, and quantified airspace volume and CFD analysis with both laminar and large eddy simulation models. Airway volume increased with linear GGA. In both CFD simulation models, velocity increased and pressure decreased after 9-mm advancement secondary to increased airway diameter and less abrupt changes in airway geometry. These results suggest that GGA may be effective in increasing airway volume and flow to address hypopharyngeal obstruction in OSA.

New acoustic model for humpback whale sound production

The mechanism by which baleen whales (Mysticeti) produce sounds has remained largely unknown, due in part to our limited knowledge of the relationship between the sound-producing anatomy and the vocal characteristics of calls. Recent studies on mysticete anatomy indicate that the laryngeal vocal folds are the sound source, and the surrounding air spaces may play an important role in airflow, and sound modification or transduction. This current study offers a theoretical model to describe the mysticete vocal production system, which is much more complex than that of typical terrestrial mammal species. Metric data from laryngeal structures and air space volumes are combined with frequency and duration ranges defined by recordings of humpback whales off the coast of Madagascar. The resulting model delivers a prediction of sound unit durations and frequency formants that are constrained by the measurements of the trachea, laryngeal sac, and nasal cavities. Results predicted by the model are comparable to those obtained from real recordings. Errors between the frequencies of real vocalizations and the frequencies estimated using our theoretical model are less than 60Hz for the low frequency band. Then, this new model should hopefully advance our growing understanding of sound generation in humpback whales, and mysticetes in general.

Human amnion epithelial cells modulate hyperoxia-induced neonatal lung injury in mice

Background aimsHuman amnion epithelial cells (hAECs) prevent pulmonary inflammation and injury in fetal sheep exposed to intrauterine lipopolysaccharide. We hypothesized that hAECs would similarly mitigate hyperoxia-induced neonatal lung injury. MethodsNewborn mouse pups were randomized to either normoxia (inspired O2 content (FiO2) = 0.21, n = 60) or hyperoxia (FiO2 = 0.85, n = 57). On postnatal days (PND) 5, 6 and 7, hAECs or sterile saline (control) was administered intraperitoneally. All animals were assessed at PND 14. ResultsHyperoxia was associated with lung inflammation, alveolar simplification and reduced postnatal growth. Administration of hAECs to hyperoxia-exposed mice normalized body weight and significantly attenuated some aspects of hyperoxia-induced lung injury (mean linear intercept and septal crest density) and inflammation (interleukin-1α, interleukin-6, transforming growth factor-β and platelet-derived growth factor-β). However, hAECs did not significantly alter changes to alveolar airspace volume, septal tissue volume, tissue-to-airspace ratio, collagen content or leukocyte infiltration induced by hyperoxia. ConclusionsIntraperitoneal administration of hAECs to neonatal mice partially reduced hyperoxia-induced lung inflammation and structural lung damage. These observations suggest that hAECs may be a potential therapy for neonatal lung disease.

Analysis of the Monotonic Lagrangian Grid as an Air Traffic Simulation Tool

A new research platform, the Air Traffic Monotonic Lagrangian Grid, has been developed to serve as a simulation tool for easy and fast testing of various air traffic system concepts. The underlying algorithm is the Monotonic Lagrangian Grid, which is a fast nearest-neighbors interaction algorithm used for sorting and tracking many moving and interacting objects. The nodes of the Monotonic Lagrangian Grid represent the locations of individual aircraft, and the grid moves at each time step as the aircraft move. The model is used to simulate a 24 h period of air traffic flow in the National Airspace System, during which there are 41,594 flights, and this requires only 79 s of wall-clock time on a single processor of a 1.3 GHz Altix. An analysis is presented of the number of nearest-neighbor nodes that must be checked to ensure adequate separation among aircraft. An investigation of the effect of removing waypoints from aircraft trajectories indicates that this may result in a significant reduction in total flight time. Finally, the model is compared with the traditional Latitude—Longitude grid approach, in which the airspace volume is partitioned into fixed stationary grid cells. Results of the comparison indicate that the main advantage of the Monotonic Lagrangian Grid method is that it is a general sorting algorithm that can sort on multiple properties, providing more computational efficiency.

Oxidative stress and nitrosative stress are involved in different stages of proteolytic pulmonary emphysema

Our aim was to investigate the role of oxidative stress in elastase-induced pulmonary emphysema. C57BL/6 mice were subjected to pancreatic porcine elastase (PPE) instillation (0.05 or 0.5U per mouse, i.t.) to induce pulmonary emphysema. Lungs were collected on days 7, 14, and 21 after PPE instillation. The control group was sham injected. Also, mice treated with 1% aminoguanidine (AMG) and inducible NO synthase (iNOS) knockout mice received 0.5U PPE (i.t.), and lungs were analyzed 21 days after. We performed bronchoalveolar lavage, biochemical analyses of oxidative stress, and lung stereology and morphometry assays. Emphysema was observed histologically at 21 days after 0.5U PPE treatment; tissues from these mice exhibited increased alveolar linear intercept and air-space volume density in comparison with the control group. TNF-α was elevated at 7 and 14 days after 0.5U PPE treatment, concomitant with a reduction in the IL-10 levels at the same time points. Myeloperoxidase was elevated in all groups treated with 0.5U PPE. Oxidative stress was observed during early stages of emphysema, with increased nitrite levels and malondialdehyde and superoxide dismutase activity at 7 days after 0.5U PPE treatment. Glutathione peroxidase activity was increased in all groups treated with 0.5U PPE. The emphysema was attenuated when iNOS was inhibited using 1% AMG and in iNOS knockout mice. Furthermore, proteolytic stimulation by PPE enhanced the expression of nitrotyrosine and iNOS, whereas the PPE+AMG group showed low expression of iNOS and nitrotyrosine. PPE stimulus also induced endothelial (e) NOS expression, whereas AMG reduced eNOS. Our results suggest that the oxidative and nitrosative stress pathways are triggered by nitric oxide production via iNOS expression in pulmonary emphysema.

Cell-specific expression of human HGF by alveolar type II cells induces remodeling of septal wall tissue in the lung: a morphometric study

Hepatocyte growth factor (HGF) is involved in development and regeneration of the lungs. Human HGF, which was expressed specifically by alveolar epithelial type II cells after gene transfer, attenuated the bleomycin-induced pulmonary fibrosis in an animal model. As there are also regions that appear morphologically unaffected in fibrosis, the effects of this gene transfer to normal lungs is of interest. In vitro studies showed that HGF inhibits the formation of the basal lamina by cultured alveolar epithelial cells. Thus we hypothesized that, in the healthy lung, cell-specific expression of HGF induces a remodeling within septal walls. Electroporation of a plasmid of human HGF gene controlled by the surfactant protein C promoter was applied for targeted gene transfer. Using design-based stereology at light and electron microscopic level, structural alterations were analyzed and compared with a control group. HGF gene transfer increased the volume of distal air spaces, as well as the surface area of the alveolar epithelium. The volume of septal walls, as well as the number of alveoli, was unchanged. Volumes per lung of collagen and elastic fibers were unaltered, but a marked reduction of the volume of residual extracellular matrix (all components other than collagen and elastic fibers) and interstitial cells was found. A correlation between the volumes of residual extracellular matrix and distal air spaces, as well as total surface area of alveolar epithelium, could be established. Cell-specific expression of HGF leads to a remodeling of the connective tissue within the septal walls in the healthy lung, which is associated with more pronounced stretching of distal air spaces at a given hydrostatic pressure during instillation fixation.

Degrees of Reality

Human patient simulators and airway training manikins are widely used to train airway management skills to medical professionals. Furthermore, these patient simulators are employed as standardized "patients" to evaluate airway devices. However, little is known about how realistic these patient simulators and airway-training manikins really are. This trial aimed to evaluate the upper airway anatomy of four high-fidelity patient simulators and two airway trainers in comparison with actual patients by means of radiographic measurements. The volume of the pharyngeal airspace was the primary outcome parameter. Computed tomography scans of 20 adult trauma patients without head or neck injuries were compared with computed tomography scans of four high-fidelity patient simulators and two airway trainers. By using 14 predefined distances, two cross-sectional areas and three volume parameters of the upper airway, the manikins' similarity to a human patient was assessed. The pharyngeal airspace of all manikins differed significantly from the patients' pharyngeal airspace. The HPS Human Patient Simulator (METI®, Sarasota, FL) was the most realistic high-fidelity patient simulator (6/19 [32%] of all parameters were within the 95% CI of human airway measurements). The airway anatomy of four high-fidelity patient simulators and two airway trainers does not reflect the upper airway anatomy of actual patients. This finding may impact airway training and confound comparative airway device studies.

Antenatal Phosphodiesterase 4 Inhibition Restores Postnatal Growth and Pulmonary Development in a Model of Chorioamnionitis in Rabbits

Chorioamnionitis is implicated in the pathophysiology of bronchopulmonary disease, and the associated inflammatory response is responsible for adverse effects on alveolar development. The aim of this work was to analyze the effects of a phosphodiesterase 4 (PDE4)-selective inhibitor, rolipram (a modulator of the inflammatory response), in an experimental model of chorioamnionitis on pulmonary development and on the processes of infection and inflammation. Rabbit mothers were assigned to four groups: 1) saline serum inoculation (controls); 2) Escherichia coli intrauterine inoculation (C+); 3) rolipram infusion (R+); and 4) E. coli inoculation + rolipram infusion (C+R+). High rates of morbility and mortality were noticed in mothers and pups (5 of 13 pregnant rabbits in groups with rolipram). Alveolar development, inflammation, and infection were analyzed in pups at day 0 and day 5. At day 0, in the context of chorioamnionitis, rolipram significantly decreased birth weight (p < 0.01) relative to that of controls (p < 0.05). At day 5, weight normalized in group C+R+ but not in group C+ relative to controls (p < 0.001); moreover, alveolar airspace volume was preserved in group C+R+ but not in group C+ (p < 0.05). Interstitial volume decreased in group C+ versus controls (p < 0.05) but was preserved in group C+R+. Specific alveolar area was not significantly modified by rolipram. No significant difference was found concerning bronchoalveolar lavage cellularity, and all blood cultures remained sterile. In this model of impaired alveologenesis, rolipram significantly preserved specific alveolar density. However, PDE4 inhibition induced antenatal fetal demise and growth retardation.

Pulmonary alveolar proteinosis: Quantitative CT and pulmonary functional correlations

ObjectiveWe assessed the relationship between quantitative computer tomography (qCT) and the pulmonary function test (PFT) or blood gas analysis in pulmonary alveolar proteinosis (PAP) patients, as well as the utility of these analyses to monitor responses to whole lung lavage (WLL) therapy. MethodsThirty-eight PAP patients simultaneously received a CT scan and PFT. Fifteen of these patients, undergoing sequential WLL for a total of 20 lavages, also underwent chest CT scans and blood gas analysis before and after WLL, and 14 of 15 patients underwent simultaneous PFT analysis. Differences between the qCT and PFT results were analyzed by canonical correlation. ResultsPAP patients with low predicted values for FVC, FEV1, DLCO and DLCO/VA indicated small airspace volume and mean lung inflation, low airspace volume/total lung volume ratio and high mean lung density. Correlation and regression analysis revealed a strong correlation between DLCO and PaO2 values with CT results. The qCT results indicated that WLL significantly decreased lung weights and mean lung densities, and improved the total airspace volume/total lung volume ratios and mean lung inflations. ConclusionQuantitative CT may be a sensitive tool for measuring the response of PAP patients to medical interventions such as WLL.

Influences of communication structural complexity on operational safety in regional airspace design

As air traffic management systems have evolved and traffic flows have increased, communications protocols have become more complex. Extra frequencies have been introduced, resulting in different frequencies being assigned to adjacent airspace volumes around airports. Consequently, pilots in close spatial proximity might not be operating on a common frequency. This could fatally inhibit timely exchange of information critical to successful avoidance of a mid-air collision. This paper considers the physical feasibility of communication between aircraft when they operate near radio frequency boundaries. It uses a simple but revealing model of aircraft operation within a multiple radio frequency structure. The model allows comprehensive descriptions of operational and failure modes once parameters such as aircraft velocities, radio frequency structures and communication transmission lengths are specified. The paper uses a novel form of nested plot for high-dimensional data to show how the failure modes are influenced by the parameters. An important conclusion is that circumstances in which problems can arise are not easily predicted during flight. Thus operational experience is not necessarily a good basis for evaluating the safety of communication system design. The model is not intended to be complete or exhaustive; its role is to demonstrate design principles and processes.