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High-flow nasal cannula (HFNC) is becoming the gold standard to treat respiratory distress at any age since it potentially provides several significant clinical advantages. An obstacle to the diffusion of this simple and effective system of oxygen therapy is the impossibility to know the optimal flow rate leading to such advantages that allows the reduction in the respiratory effort without causing hyperinflation. To assist clinicians during HFNC treatment in setting the optimal flow rate and in determining the most relevant parameters related to respiratory mechanics and the effort of the patient, we developed a new programmable data monitoring, acquisition, and elaborating system (Pro_HFNC). The application of Pro_HFNC is fully compatible with HFNC as it is interfaced with patient through a facial mask and two specific catheters. The unavoidable and unpredictable loss of air flow occurring around the contour of the mask is evaluated and compensated by a specific algorithm implemented by Pro_HFNC. Our preliminary clinical trials on pediatric patients treated with HFNC show that Pro_HFNC is actually capable to detect for any specific patient both the lower threshold of the delivered flow beyond which the benefits of HFNC application are reached and all the parameters useful for a complete evaluation of the respiratory profile. Pro_HFNC can really help physicians in setting the optimal flow rate during HFNC treatment, thus allowing for the most effective HFNC performance. [ABSTRACT FROM AUTHOR]

Background: While the development of CT imaging technique has brought cognition of in vivo organs, the resolution of CT images and their static characteristics have gradually become barriers of microscopic tissue research. Purpose: Previous research used the finite element method to study the airflow and gas exchange in the alveolus and acinar to show the fate of inhaled aerosols and studied the diffusive, convective, and sedimentation mechanisms. Our study combines these techniques with CT scan simulation to study the mechanisms of respiratory movement and its imaging appearance. Methods: We use 3D fluid‐structure interaction simulation to study the movement of an ideal alveolus under regular and forced breathing situations and ill alveoli with different tissue elasticities. Additionally, we use the Monte Carlo algorithm within the OpenGATE platform to simulate the computational CT images of the dynamic process with different designated resolutions. The resolutions show the relationship between the kinematic model of the human alveolus and its imaging appearance. Results: The results show that the alveolus and the wall thickness can be seen with an image resolution smaller than 15.6 μm. With ordinary CT resolution, the alveolus is expressed with four voxels. Conclusions: This is a preliminary study concerning the imaging appearance of the dynamic alveolus model. This technique will be used to study the imaging appearance of the dynamic bronchial tree and the lung lobe models in the future. [ABSTRACT FROM AUTHOR]

Obstructive Sleep Apnea (OSA) is a respiratory disorder characterized by frequent breathing pauses during sleep. The apnea–hypopnea index is a measure used to assess the severity of sleep apnea and the hourly rate of respiratory events. Despite numerous commercial devices available for apnea diagnosis and early detection, accessibility remains challenging for the general population, leading to lengthy wait times in sleep clinics. Consequently, research on monitoring and predicting OSA has surged. This comprehensive paper reviews devices, emphasizing distinctions among representative apnea devices and technologies for home detection of OSA. The collected articles are analyzed to present a clear discussion. Each article is evaluated according to diagnostic elements, the implemented automation level, and the derived level of evidence and quality rating. The findings indicate that the critical variables for monitoring sleep behavior include oxygen saturation (oximetry), body position, respiratory effort, and respiratory flow. Also, the prevalent trend is the development of level IV devices, measuring one or two signals and supported by prediction software. Noteworthy methods showcasing optimal results involve neural networks, deep learning, and regression modeling, achieving an accuracy of approximately 99%. [ABSTRACT FROM AUTHOR]

High-flow nasal cannula (HFNC) is becoming the gold standard to treat respiratory distress at any age since it potentially provides several significant clinical advantages. An obstacle to the diffusion of this simple and effective system of oxygen therapy is the impossibility to know the optimal flow rate leading to such advantages that allows the reduction in the respiratory effort without causing hyperinflation. To assist clinicians during HFNC treatment in setting the optimal flow rate and in determining the most relevant parameters related to respiratory mechanics and the effort of the patient, we developed a new programmable data monitoring, acquisition, and elaborating system (Pro_HFNC). The application of Pro_HFNC is fully compatible with HFNC as it is interfaced with patient through a facial mask and two specific catheters. The unavoidable and unpredictable loss of air flow occurring around the contour of the mask is evaluated and compensated by a specific algorithm implemented by Pro_HFNC. Our preliminary clinical trials on pediatric patients treated with HFNC show that Pro_HFNC is actually capable to detect for any specific patient both the lower threshold of the delivered flow beyond which the benefits of HFNC application are reached and all the parameters useful for a complete evaluation of the respiratory profile. Pro_HFNC can really help physicians in setting the optimal flow rate during HFNC treatment, thus allowing for the most effective HFNC performance.

Robin Sequence (RS) is a potentially fatal craniofacial condition characterized by undersized jaw, posteriorly displaced tongue, and resultant upper airway obstruction (UAO). Accurate assessment of UAO severity is crucial for management and diagnosis of RS, yet current evaluation modalities have significant limitations and no quantitative measures of airway resistance exist. In this study, we combine 4-dimensional computed tomography and computational fluid dynamics (CFD) to assess, for the first time, UAO severity using fluid dynamic metrics in RS patients. Dramatic intrapopulation differences are found, with the ratio between most and least severe patients in breathing resistance, energy loss, and peak velocity equal to 40:1, 20:1, and 6:1, respectively. Analysis of local airflow dynamics characterized patients as presenting with primary obstructions either at the location of the tongue base, or at the larynx, with tongue base obstructions resulting in a more energetic stenotic jet and greater breathing resistance. Finally, CFD-derived flow metrics are found to correlate with the level of clinical respiratory support. Our results highlight the large intrapopulation variability, both in quantitative metrics of UAO severity (resistance, energy loss, velocity) and in the location and intensity of stenotic jets for RS patients. These results suggest that computed airflow metrics may significantly improve our understanding of UAO and its management in RS. [ABSTRACT FROM AUTHOR]

Abnormal breathing can be a symptom of an unhealthy status. Conventional diagnostic exams involve cumbersome and intrusive instrumentation, such as nasal cannulas, that is, uncomfortable for the user and that, most of the times, do not consider the breathing asymmetries between the two nostrils. This article describes a two-channel flexible epidermal sensor for the wireless and less-invasive bilateral monitoring of nasal breathing based on temperature measurement. The device is suitable to adhere to the prolabium and comprises two coupled T-match antennas whose Ultra-High Frequency (UHF) Radio-Frequency Identification (RFID) Integrated Circuits (ICs) are placed at the entrance of the nostrils. They are provided with embedded temperature sensors so that they implement both sensing and transmission of the data. A measurement campaign is carried out to provide a quantitative characterization of the dual-channel device as a breath sensor by comparison with a conventional flow meter. The two nostrils can be independently monitored due to a negligible cross-sensitivity of the two ICs’ temperature data. Moreover, temperature-based measurements proved capable to reproduce typical clinical breathing features, with less than 12% uncertainty with respect to flow waveforms. [ABSTRACT FROM AUTHOR]

Obstructive Sleep Apnea (OSA) is a respiratory disorder characterized by frequent breathing pauses during sleep. The apnea–hypopnea index is a measure used to assess the severity of sleep apnea and the hourly rate of respiratory events. Despite numerous commercial devices available for apnea diagnosis and early detection, accessibility remains challenging for the general population, leading to lengthy wait times in sleep clinics. Consequently, research on monitoring and predicting OSA has surged. This comprehensive paper reviews devices, emphasizing distinctions among representative apnea devices and technologies for home detection of OSA. The collected articles are analyzed to present a clear discussion. Each article is evaluated according to diagnostic elements, the implemented automation level, and the derived level of evidence and quality rating. The findings indicate that the critical variables for monitoring sleep behavior include oxygen saturation (oximetry), body position, respiratory effort, and respiratory flow. Also, the prevalent trend is the development of level IV devices, measuring one or two signals and supported by prediction software. Noteworthy methods showcasing optimal results involve neural networks, deep learning, and regression modeling, achieving an accuracy of approximately 99%.

Respiratory diseases are a leading cause of death worldwide. The prevalence of sleep apnea, its cardiovascular consequences, postoperative respiratory instability and severe respiratory syndromes further highlight the importance of respiratory monitoring. Typical methods, however, rely on obtrusive nasal cannulas and belts. Impedance pneumography (IP) is a promising bioimpedance application which aims to estimate respiratory parameters from the thorax impedance. Currently, IP configurations require large inter-electrode distances, diminishing its applicability in a wearable context. We propose an IP configuration with 55 mm spacing using our recently presented sensor patch. In a study including 10 healthy subjects, respiratory rate (RR) and flow are estimated in the supine, lateral and prone position. Using time-delay neural network regression, RR errors below 1 bpm, flow correlations of 0.81 and relative flow errors of 38 % with respect to a pneumotachometer reference were achieved. We conclude that high accuracy RR estimation is possible in a 55 mm IP configuration. Respiratory flow can be roughly estimated. Further research combining several biosignals for a more robust, wearable flow estimation is recommended.

In recent years, respiratory monitoring has gained attention due to the high prevalence and severe consequences of sleep apnea, post-anesthesia respiratory instability and respiratory diseases. Nevertheless, respiratory monitoring oftentimes relies on obtrusive masks and belts, which are unsuitable for wearable, long-term monitoring. Impedance pneumography (IP) is a bioimpedance method aiming to assess respiratory parameters unobtrusively. However, most IP configurations require far-spaced electrodes. Based on our recent work on wearable IP, we propose a dual-lead, wearable IP setup with 55 mm electrode spacing to estimate respiratory flow and rate (RR). Using our recently presented multimodal patch stethoscope as well as commercial systems, we conducted a study including 10 healthy subjects which were recorded in the supine, lateral and prone position. Using time-delay neural networks, we achieved RR estimation errors below 0.6 breaths per minute and flow correlations of 0.88 with relative errors of 25 % to a pneumotachometer reference. We conclude that dual-lead IP increases the performance of respiratory signal estimation compared to a single lead and recommend research in the area of subject position dependency and movement artefacts.

Respiratory flow, expired O2, and CO2 were measured during voluntary participation while spontaneously breathing in 13 confirmed healthy, male California sea lions (Zalophus californianus; body mass [Mb] range: 49 to 130 kg). Expiratory and inspiratory flow (and '), tidal volume (VTexp and VTinsp), and breath durations (Texp, Tinsp, and Ttot) were collected on land (lying down in sternal recumbency and sitting up) and floating in water to test the hypothesis that lung function changes with body position and on land versus in water. For sea lions on land, no differences were seen in any of the lung function values when comparing lying down versus sitting up. However, when comparing animals on land versus in water, both Tap and Tup decreased and. and. increased, while the VTexp and VT-msp remained the same. The resting mass-specific VT (25.1 ± 1.7 ml kg-1) in the current study was approximately 24 to 30% of the estimated total lung capacity. We also measured breath-by-breath gas uptake to determine the O2 consumption rates () and CO2 production rates VC02) g rest on land and in water. There were no differences in VO2 or vco2 on land as compared with water, and the average estimated values were 0.58 ± 0.22 l O2 min-1 (range: 0.24 to 1.01 l O2 min-1) and 0.50 ± 0.19 l CO2 min-1 (range: 0.22 to 0.89 l CO2 min-1), respectively, which agrees with results from other studies on otariids. Additionally, the allometric mass-exponent for Vt and VO2 were 1.13 to 1.20 and 0.86, respectively. These data are the first reported estimates of metabolic rate and lung function in confirmed healthy California sea lions. [ABSTRACT FROM AUTHOR]

Both Respiratory Flow (RF) and Respiratory Motion (RM) are visible in thermal recordings of infants. Monitoring these two signals usually requires landmark detection for the selection of a region of interest. Other approaches combine respiratory signals coming from both RF and RM, obtaining a Mixed Respiratory (MR) signal. The detection and classification of apneas, particularly common in preterm infants with low birth weight, would benefit from monitoring both RF and RM, or MR, signals. Therefore, we propose in this work an automatic RF pixel detector not based on facial/body landmarks. The method is based on the property of RF pixels in thermal videos, which are in areas with a smooth circular gradient. We defined 5 features combined with the use of a bank of Gabor filters that together allow selection of the RF pixels. The algorithm was tested on thermal recordings of 9 infants amounting to a total of 132 min acquired in a neonatal ward. On average the percentage of correctly identified RF pixels was 84%. Obstructive Apneas (OAs) were simulated as a proof of concept to prove the advantage in monitoring the RF signal compared to the MR signal. The sensitivity in the simulated OA detection improved for the RF signal reaching 73% against the 23% of the MR signal. Overall, the method yielded promising results, although the positioning and number of cameras used could be further optimized for optimal RF visibility.

Studies of flow through the human airway have shown that inhalation time (IT) and secondary flow structures can play important roles in particle deposition. However, the effects of varying IT in conjunction with the respiratory rate (RR) on airway flow remain unknown. Using three-dimensional numerical simulations of oscillatory flow through an idealized airway model (consisting of a mouth, glottis, trachea, and symmetric double bifurcation) at a trachea Reynolds number (Re) of 4200, we investigated how varying the ratio of IT to breathing time (BT) from 25% to 50% and RR from 10 breaths per minute (bpm) corresponding to a Womersley number (Wo) of 2.41 to 1000 bpm (Wo = 24.1) impacts airway flow characteristics. Irrespective of IT/BT, axial flow during inhalation at tracheal cross-sections was non-uniform for Wo = 2.41, as compared to centrally concentrated distribution for Wo = 24.1. For a given Wo and IT/BT, both axial and secondary (lateral) flow components unevenly split between left and right branches of a bifurcation. Irrespective of Wo, IT/BT and airway generation, lateral dispersion was a stronger transport mechanism than axial flow streaming. Discrepancy in the oscillatory flow relation Re/Wo2 = 2 L/D (L = stroke length; D = trachea diameter) was observed for IT/BT ≠ 50%, as L changed with IT/BT. We developed a modified dimensionless stroke length term including IT/BT. While viscous forces and convective acceleration were dominant for lower Wo, unsteady acceleration was dominant for higher Wo.

Highly integrated analog frontends for biosignal acquisition facilitate the development of complex yet small vital sign monitors capable of passive sensing. However, the established gold standards for sensor positioning cover large areas of the patient's body. Especially when measuring respiration, an important parameter in postoperative care and sleep monitoring, masks, belts or nasal cannulas are used. Therefore, estimation techniques such as photoplethysmography (PPG) derived respiration have emerged. Fingertip PPG is a widely used modality acquired optically at the peripheral vascular system. While miniaturized reflective PPG systems are available, their integration can prove problematic in certain scenarios, especially with textiles. We propose impedance plethysmography as a well integrable alternative to PPG for the estimation of absolute respiratory flow and rate. Employing nested cross-validation and wrapper techniques in a model and feature selection framework, we analyzed different polynomial and multilayer perceptron regression models as well as feature sets. In a pilot study, we achieved relative errors of 1.5 % for respiratory rate and 59 % for flow estimation using seven time-domain features of the acquired impedance signal. We conclude that impedance plethysmography can be a promising alternative for highly integrated and unobtrusive respiratory rate estimation as well as rough flow estimation. [ABSTRACT FROM AUTHOR]

Measuring work of breathing (WOB) is an intricate task during high-flow nasal cannula (HFNC) therapy because the continuous unidirectional flow toward the patient makes pneumotachography technically difficult to use. We implemented a new method for measuring WOB based on a differential pneumotachography (DP) system, equipped with one pneumotachograph inserted in the HFNC circuit and another connected to a monitoring facemask, combined with a leak correction algorithm (LCA) that corrects flow measurement errors arising from leakage around the monitoring facemask. To test this system, we used a mechanical lung model that provided data to compare LCA-corrected respiratory flow, volume and time values with effective values obtained with a third pneumotachograph used instead of the LCA to measure mask flow leaks directly. Effective and corrected volume and time data showed high agreement (Bland–Altman plots) even at the highest leak. Studies on two healthy adult volunteers confirmed that corrected respiratory flow combined with esophageal pressure measurements can accurately determine WOB (relative error < 1%). We conclude that during HFNC therapy, a DP system combined with a facemask and an algorithm that corrects errors due to flow leakages allows pneumotachography to measure reliably the respiratory flow and volume data needed for calculating WOB. [ABSTRACT FROM AUTHOR]

In this Review, we focus on the functional properties of the respiratory system of pinnipeds and cetaceans, and briefly summarize the underlying anatomy; in doing so, we provide an overview of what is currently known about their respiratory physiology and mechanics. While exposure to high pressure is a common challenge among breath-hold divers, there is a large variation in respiratory anatomy, function and capacity between species - howare these traits adapted to allow the animals to withstand the physiological challenges faced during dives? The ultra-deep diving feats of some marine mammals defy our current understanding of respiratory physiology and lung mechanics. These animals cope daily with lung compression, alveolar collapse, transient hyperoxia and extreme hypoxia. By improving our understanding of respiratory physiology under these conditions, we will be better able to define the physiological constraints imposed on these animals, and how these limitations may affect the survival of marine mammals in a changing environment. Many of the respiratory traits to survive exposure to an extreme environment may inspire novel treatments for a variety of respiratory problems in humans. [ABSTRACT FROM AUTHOR]

The time-varying flow is studied experimentally in an anatomically accurate model of the human airways from the mouth through several generations of bronchial branching. The airway geometry is obtained from the CT scan of a healthy adult male of normal height and build. The three-component, three-dimensional mean velocity field is obtained throughout the entire model using phase-locked Magnetic Resonance Velocimetry. A pulsatile pump drives a sinusoidal waveform (inhalation and exhalation) with frequency and stroke-length such that the mean trachea Reynolds number at peak inspiration is 4200 and the Womersley number is 7. Integral parameters are defined to quantify the degree of velocity profile non-uniformity (related to axial dispersion) and secondary flow strength (lateral dispersion). It is found that the extrathoracic airways significantly modify the tracheal flow and that the flow at the first bifurcation is highly asymmetric. The effect of flow oscillation is to produce time dependent flow features which are asymmetric with respect to the acceleration and deceleration periods surrounding peak inhalation and exhalation. This is most pronounced in regions of separation and on the secondary flow structure, which are sensitive to local attributes of the real anatomy. This is reflected in the integral parameters, which behave non-monotonically between successive bronchial generations. In general, the measured oscillatory flow in a realistic anatomy confirms many trends derived from idealized models but also possesses qualitatively different large scale flow structures as compared to idealized representations of the upper airways. [ABSTRACT FROM AUTHOR]

We present a comparison of the flow characteristics in an idealized smooth trachea model and a second model which has a roughness simulating cartilaginous rings. We use refractive index-matched particle image velocimetry (PIV) to measure the velocity field in a two-generation model of the trachea and main bronchi. The flow rate has a trachea-based Reynolds number Re =2800, which is comparable to a resting state. Our results show considerable differences between both cases, the most important of which is the size and magnitude of recirculation zones at the inlet of both bronchi. The smooth case shows a larger separation bubble at the bronchi entrance, which may retain aerosols and have different effects on particles of different sizes. Furthermore, the smooth case displays a higher vorticity along the bottom walls of the bronchi, while a higher vorticity is seen along the trachea walls in the ׳ringed׳ model. These findings suggest that modeling the trachea and main bronchi as smooth tubes may not be justified, since the flow conditions in lower generations will be affected by these differences. [ABSTRACT FROM AUTHOR]

In reduced-order (0D/1D) blood or respiratory flow models, pressure losses at junctions are usually neglected. However, these may become important where velocities are high and significant flow redirection occurs. Current methods for estimating losses rely on relatively complex empirical equations that are only valid for specific junction geometries and flow regimes. In pulsatile multi-directional flows, switching between empirical equations upon reversing flow may introduce unrealistic discontinuities in simulated haemodynamic waveforms. Drawing from work by Bassett et al. (SAE Trans 112:565-583, 2003), we therefore developed a unified method (Unified0D) for estimating loss coefficients that can be applied to any junction (i.e. any number of branches at any angle) and any flow regime. Discontinuities in simulated waveforms were avoided by extending Bassett et al.'s control volume-based method to incorporate a 'pseudodatum' supplier branch, an imaginary effective vessel containing all inflow to the junction. Energy exchange between diverging flow streams was also accounted for empirically. The formulation was validated using high resolution computational fluid dynamics in a wide range flow conditions and junction configurations. In a pulsatile 1D simulation exhibiting transitions between four different flow regimes, the new formulation produced smooth transitions in calculated pressure losses. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

BACKGROUND: Most portable bi-level positive airway pressure devices are not equipped with air-oxygen blenders for precisely regulating oxygen concentrations, and supplemental oxygen must be added to increase the FIO2. Very few studies have investigated the factors that affect FIO2, and their conclusions have been inconsistent. We investigated in vitro noninvasive ventilation (NIV) parameters and their effects on FIO2, particularly the effect of the oxygen injection site. METHODS: NIV was simulated with a test lung and manikin setup. FIO2 was measured with 4 oxygen injection sites (mask, in front of the exhalation valve, at the humidifier outlet, and proximal to the ventilator), with 3 exhalation valve types, with 2 oxygen flows, and with 4 combinations of inspiratory and expiratory pressure. RESULTS: Oxygen flow, inspiratory and expiratory pressure, and exhalation valve type all affected FIO2. For a given oxygen flow, the oxygen injection site was the most important factor that affected FIO2. The oxygen injection site that was closest to the patient (on the mask) had the higher FIO2 (P < .001). CONCLUSIONS: The oxygen injection site had the greatest effect on FIO2 during NIV. [ABSTRACT FROM AUTHOR]

Tracheal respiratory sound analysis is a simple and non-invasive way to study the pathophysiology of the upper airway and has recently been used for acoustic estimation of respiratory flow and sleep apnea diagnosis. However in none of the previous studies was the respiratory flow-sound relationship studied in people with obstructive sleep apnea (OSA), nor during sleep. In this study, we recorded tracheal sound, respiratory flow, and head position from eight non-OSA and 10 OSA individuals during sleep and wakefulness. We compared the flow-sound relationship and variations in model parameters from wakefulness to sleep within and between the two groups. The results show that during both wakefulness and sleep, flow-sound relationship follows a power law but with different parameters. Furthermore, the variations in model parameters may be representative of the OSA pathology. The other objective of this study was to examine the accuracy of respiratory flow estimation algorithms during sleep: we investigated two approaches for calibrating the model parameters using the known data recorded during either wakefulness or sleep. The results show that the acoustical respiratory flow estimation parameters change from wakefulness to sleep. Therefore, if the model is calibrated using wakefulness data, although the estimated respiratory flow follows the relative variations of the real flow, the quantitative flow estimation error would be high during sleep. On the other hand, when the calibration parameters are extracted from tracheal sound and respiratory flow recordings during sleep, the respiratory flow estimation error is less than 10%. [ABSTRACT FROM AUTHOR]

When you reach with your straw for the final drops of a milkshake, the liquid forms a train of plugs that flow slowly initially because of the high viscosity. They then suddenly rupture and are replaced with a rapid airflow with the characteristic slurping sound. Trains of liquid plugs also are observed in complex geometries, such as porous media during petroleum extraction, in microfluidic two-phase flows, or in flows in the pulmonary airway tree under pathological conditions. The dynamics of rupture events in these geometries play the dominant role in the spatial distribution of the flow and in determining how much of the medium remains occluded. Here we show that the flow of a train of plugs in a straight channel is always unstable to breaking through a cascade of ruptures. Collective effects considerably modify the rupture dynamics of plug trains: Interactions among nearest neighbors take place through the wetting films and slow down the cascade, whereas global interactions, through the total resistance to flow of the train, accelerate the dynamics after each plug rupture. In a branching tree of microchannels, similar cascades occur along paths that connect the input to a particular output. This divides the initial tree into several independent subnetworks, which then evolve independently of one another. The spatiotemporal distribution of the cascades is random, owing to strong sensitivity to the plug divisions at the bifurcations. [ABSTRACT FROM AUTHOR]

The convective transport of fluid within the human upper airways is investigated in a transparent model of the tracheobronchial tree. Oscillatory flow through the branching network with six generations was studied at varying Reynolds numbers between 400 and 2600 and Womersley numbers from 5.5 to 12.3 in the trachea representing clinical conditions during high frequency oscillatory ventilation. The flow partitioning within the model was visualized using advection of neutrally buoyant tracer particles, which were illuminated by short light pulses and recorded by a high speed camera. Integration of the particle locations for a large number of cycles provides the probability distribution of particles passing certain branches within the bifurcating network, and thus, the dispersion of particles in the airways. The results show the different characteristics of flow partitioning at varying Womersley and Reynolds numbers. [ABSTRACT FROM AUTHOR]

Abstract: Chronic obstructive pulmonary disease (COPD) is one of the most common diseases in human community. The COPD always results in inflammation that leads to narrowing and obstruction of the airways. The obstructive airways have significant effect on respiratory flow. In order to understand the flow phenomenon in such obstructive airways, four three-dimensional four-generation lung models based on the 23-generation model of Weibel [1963. Morphometry of the Human Lung. Springer, Academic Press, Berlin, New York] are generated. The fully three-dimensional incompressible laminar Navier–Stokes equations are solved using computational fluid dynamics (CFD) solver on unstructured tetrahedral meshes. Therein, a symmetric four-generation airway model is served as the reference, the other three models are considered to be obstructed at each generation, respectively. The calculation results show that the obstructive airway has significant influence on the air flow in both up- and down-stream airways and it even results in flow separation in the conjunction region. The re-circulation cell blocks the air from entering the downstream branches. This may be the reason why COPD patients should breathe gently, and this also provides some valuable information for medicine powder deposition. [Copyright &y& Elsevier]

Abstract: The effect of inlet velocity profile on the flow features in obstructed airways is investigated in this study. In reality, the inlet velocity distributions on such models, which are extracted from medial branches of natural human lung, should be neither uniform, nor symmetric parabolic, but skewed-parabolic due to having been skewed by the upper carina ridges. Four different three-dimensional three-generation models based on the 23 generations model of Weibel have been considered, respectively. The fully three-dimensional incompressible laminar Navier–Stokes equations and continuity equation have been solved using CFD solver on unstructured tetrahedral meshes. To reduce the complexity of the simulations, only one Reynolds number of 900 was used in this calculation. Four types of inlet boundary conditions, namely uniform, parabolic, positive-skewed parabolic (skewed to the positive -direction), and negative-skewed parabolic, were imposed on the obstructed airway models, which were considered to be obstructed at either the second generation or the third generation airways, respectively. The results show that the inlet velocity profile has significant influence on the flow patterns, mass distributions, and pressure drops in either the symmetric model, or the three obstructed models. The three generation airways may not be enough to study the bifurcation flow in chronic obstructive pulmonary disease (COPD) airways, and a four-generation or more airway model is necessary to get better predictive results. [Copyright &y& Elsevier]

• Comparison of various turbulence models for RANS predictions of stationary inhalation • A Reynolds-stress turbulence model yielded good agreement with experiments and LES • Lagrangian particle tracking with turbulent dispersion modelling yields over-prediction of deposition • This spurious drift may be only accurately corrected by a Reynolds-stress turbulence model • Wall effects in drag and lift reduce deposition in the airways for larger particles Airflow and aerosol deposition in the human airways are important aspects for applications such as pulmonary drug delivery and human exposure to aerosol pollutants. Numerical simulations are widely used nowadays to shed light in airflow features and particle deposition patterns inside the airways. For that purpose, the Euler/Lagrange approach is adopted for predicting flow field and particle deposition through point-particle tracking. Steady-state RANS (Reynolds-averaged Navier-Stokes) computations of flow evolution in an extended lung model applying different turbulence models were conducted and compared to measurements as well as high resolution LES (large-eddy simulations) for several flow rates. In addition, various inlet boundary conditions were considered and their influence on the predicted flow field was analysed. The results showed that the mean velocity field was simulated reasonably well, however, turbulence intensity was completely under-predicted by two-equation turbulence models. Only a Reynolds-stress model (RSM) was able predicting a turbulence level comparable to the measurements and the high resolution LES. Remarkable reductions in wall deposition were observed when wall effects were accounted for in the drag and lift force expressions. Naturally, turbulence is an essential contribution to particle deposition and it is well known that two-equation turbulence models considerably over-predict deposition due to the spurious drift effect. A full correction of this error is only possible in connection with a Reynolds-stress turbulence model whereby the predicted deposition in dependence of particle diameter yielded better agreement to the LES predictions. Specifically, with the RSM larger deposition is predicted for smaller particles and lower deposition fraction for larger particles compared to LES. The local deposition fraction along the lung model was numerically predicted with the same trend as found from the measurements, however the values in the middle region of the lung model were found to be somewhat larger. [Display omitted] [ABSTRACT FROM AUTHOR]

Both Respiratory Flow (RF) and Respiratory Motion (RM) are visible in thermal recordings of infants. Monitoring these two signals usually requires landmark detection for the selection of a region of interest. Other approaches combine respiratory signals coming from both RF and RM, obtaining a Mixed Respiratory (MR) signal. The detection and classification of apneas, particularly common in preterm infants with low birth weight, would benefit from monitoring both RF and RM, or MR, signals. Therefore, we propose in this work an automatic RF pixel detector not based on facial/body landmarks. The method is based on the property of RF pixels in thermal videos, which are in areas with a smooth circular gradient. We defined 5 features combined with the use of a bank of Gabor filters that together allow selection of the RF pixels. The algorithm was tested on thermal recordings of 9 infants amounting to a total of 132 min acquired in a neonatal ward. On average the percentage of correctly identified RF pixels was 84 % . Obstructive Apneas (OAs) were simulated as a proof of concept to prove the advantage in monitoring the RF signal compared to the MR signal. The sensitivity in the simulated OA detection improved for the RF signal reaching 73 % against the 23 % of the MR signal. Overall, the method yielded promising results, although the positioning and number of cameras used could be further optimized for optimal RF visibility. [ABSTRACT FROM AUTHOR]

Flow in a symmetric bifurcation model of analytically known geometry was investigated experimentally under oscillatory flow conditions. The duration of the inspiratory and expiratory phases were set to be equal during the oscillatory period. A two velocity component laser Doppler anemometer was used to interrogate the flow field. Three different flow rates through the bifurcation were investigated. The peak Reynolds numbers, based on peak flow rates, were 700, 1278, and 2077. The Womersley number was set to 4.3 and it was kept at the same value for the three different flow rates. The results suggest that under the conditions studied a quasisteady flow assumption for oscillatory flow is valid for only about 50% of the oscillatory period, or it is limited to represent the oscillatory flow only in the vicinity of peak inspiration and peak expiration. Complex transport phenomena that occur during the transition between the respiratory phases cannot be elucidated and analyzed by quasisteady equivalents. © 1998 Biomedical Engineering Society. PAC98: 8745Hw, 8710+e, 4780+v, 4262Be, 8764-t [ABSTRACT FROM AUTHOR]