7 research outputs found
Computational fluid dynamics comparison of the upper airway velocity, pressure, and resistance in cats using an endotracheal tube or a supraglottic airway device
IntoductionIn veterinary medicine, airway management of cats under general anesthesia is performed with an endotracheal tube (ETT) or supraglottic airway device (SGAD). This study aims to describe the use of computational fluid dynamics (CFD) to assess the velocities, pressures, and resistances of cats with ETT or SGAD.MethodsA geometrical reconstruction model of the device, trachea, and lobar bronchi was carried out from computed tomography (CT) scans that include the head, neck, and thorax. Twenty CT scans of cats under general anesthesia using ETT (n = 10) and SGAD (n = 10) were modeled and analyzed. An inspiratory flow of 2.4 L/min was imposed in each model and velocity (m/s), general and regional pressures (cmH2O) were computed. General resistance (cmH2O/L/min) was calculated using differential pressure differences between the device inlet and lobar bronchi. Additionally, regional resistances were calculated at the device’s connection with the breathing circuit (region A), at the glottis area for the SGAD, and the area of the ETT exit (bevel) (region B) and the device itself (region C).ResultsRecirculatory flow and high velocities were found at the ETT’s bevel and at the glottis level in the SGAD group. The pressure gradient (Δp) was more enhanced in the ETT cases compared with the SGAD cases, where the pressure change was drastic. In region A, the Δp was higher in the ETT group, while in regions B and C, it was higher in the SGAD group. The general resistance was not statistically significant between groups (p = 0.48). Higher resistances were found at the region A (p = <0.001) in the ETT group. In contrast, the resistance was higher in the SGAD cases at the region B (p = 0.001).DiscussionOverall, the provided CT-based CFD analysis demonstrated regional changes in airway pressure and resistance between ETT and SGAD during anesthetic flow conditions. Correct selection of the airway device size is recommended to avoid upper airway obstruction or changes in flow parameters
Pulmonary fluid dynamics and aerosol drug delivery in the upper tracheobronchial airways under mechanical ventilation conditions
The effects of mechanical ventilation conditions on fluid flow and particle deposition were studied in a computer model of the human airways. The frequency with which aerosolized drugs are delivered to mechanically ventilated patients demonstrates the importance of understanding the effects that ventilation parameters have on particle deposition in the human airways. Past studies that modeled particle deposition in silico frequently used an idealized geometry with steady inlet conditions. With recent advancements in computational power and medical imaging capabilities, studies have begun to use more realistic geometries or unsteady inlet conditions that model normal breathing. This study focuses specifically on the effects of mechanical ventilation waveforms using a computer model of the airways from the endotracheal tube to generation 07, in the lungs of a patient undergoing mechanical ventilation treatment. Computational fluid dynamics (CFD), using the commercial software package ANSYS® CFX®, combined with realistic respiratory waveforms commonly used by commercial mechanical ventilators, large eddy simulation (LES) to model turbulence, and user defined particle force models were applied to solve for fluid flow and particle deposition parameters. The endotracheal tube (ETT) was found to be an important geometric feature, causing a fluid jet towards the right main bronchus, increased turbulence, and a recirculation zone in the right main bronchus. In addition to the enhanced deposition seen at the carinas of the airway bifurcations, enhanced deposition was also seen in the right main bronchus due to impaction and turbulent dispersion resulting from the fluid structures created by the ETT. The dependence of local particle deposition on respiratory waveforms implies that great care should be taken when selecting ventilation parameters --Abstract, page iii
Pulmonary Gas Transport and Drug Delivery in a Patient Specific Lung Model During Invasive High Frequency Oscillatory Ventilation
The objective of this dissertation research was to investigate gas transport, mixing and aerosol-drug delivery during high frequency oscillatory ventilation (HFOV) for various ventilator specific conditions that are vital to critical care clinicians. A large eddy simulation based computational fluid dynamics approach was used in a patient specific human lung model to analyze the effect of invasive HFOV on patient management. Different HFOV waveform shapes and frequencies was investigated and the square waveform was found to be most efficient for gas mixing; resulting in the least wall shear stress on the lung epithelium layer thereby reducing the risk of barotrauma to both airways and the alveoli for patients undergoing therapy. Traditional (outlet) boundary conditions based on mass fraction or outlet pressures were found to be inadequate in describing the complex flow physics that occurs during HFOV. Physiological boundary conditions that used the time-dependent pressure coupled with the airways resistance and compliance (R&C) were derived and used for the first time to investigate the lung lobar ventilation and gas exchange for accurate HFOV modeling. A Lagrangian approach was then used to model gas-solid two-phase flow that allowed investigation of the potential of aerosol-drug delivery under HFOV treatment. We report, for the first time, computational fluid dynamics studies to investigate the possibilities of aerosol drug delivery under HFOV. Understanding the role of different carrier gases on the gas exchange and particle deposition, which may allow for optimum drug delivery and ventilation strategy during HFOV. Increasing the operating frequency resulted in a significant change in the global and local deposition indicating strong dependency on the frequency, which could be beneficial for the targeted drug delivery. The global deposition as a fraction of the total injected particles at the endotracheal tube inlet was equivalent to the cases of normal breathing and conventional mechanical ventilation signifying a potential for efficient drug delivery during HFOV. In addition, HFOV had a unique characterization of the local particle deposition due to the rapid ventilation process and a strong influence of the endotracheal tube jet. Very often during ventilation therapy, a clinician uses a cocktail of various gases to enhance targeted therapy. To quantify this process for a futuristic HFOV based patient management, we undertook detailed studies to understand the role of carrier gas properties in gas exchange and particle transport during HFOV. A substantial amplification of the pendelluft flow was achieved by utilizing a low-density carrier gas instead of air, which resulted in gas exchange improvement. Reducing the carrier gas density was found to significantly alter the aerosol-drug delivery under HFOV management. As the density decreased, the deposition fraction in the upper tracheobronchial tree decreased, indicating enhancement of the lung periphery delivery. Furthermore, the filtered aerosol-drug in the ventilator circuit could be significantly reduced by using Heliox, and further reduction could be achieved by reducing the operating frequency. In general, high-frequency oscillatory ventilation therapy could be improved under Heliox with greater content of Helium, thereby reducing the lung hyperinflation risk
CFD simulation of an industrial spiral refrigeration system
This is the final version. Available on open access from MDPI via the DOI in this recordIn the food industry, heating and cooling are key processes where CFD can play an important role in improving quality, productivity and reducing energy costs. Cooling products after baking is crucial for storage and transportation; the product has to be cooled efficiently to a specified temperature (often to fulfill regulatory requirements) whilst preserving its quality. This study involves the analysis of spiral cooling refrigerators used in cooling food products, in this case, Cornish Pasties. Three separate sets of CFD models were developed and validated against experimental data taken in the laboratory and measurements taken in use in industry. In the first set of models a full CFD model was developed of a refrigeration spiral including the pasties, and used to study the heat transfer from the products to the air. Further simulations were carried out on individual pasties to explore the pasty cooling and heat transfer to the air in more detail, with the pasty geometry being determined from MRI scans. In the final set of simulations, Image Based Meshing (IBM) was used to determine the interior structure of the pasty and develop a full heat conduction model of the interior, which was compared with separate laboratory experiments using jets of cold air to cool the pasty. In all cases, good agreement was obtained between the CFD results and experimental data, whilst the CFD simulations provide valuable information about the air flows and cooling in the industrial system.Innovate U
In vitro methods to predict aerosol drug deposition in normal adults
This research was aimed at the development and validation of new in vitro methods capable of predicting in vivo drug deposition from dry powder inhalers, DPIs, in lung-normal human adults. Three physical models of the mouth, throat and upper airways, MT-TB, were designed and validated using the anatomical literature. Small, medium and large versions were constructed to cover approximately 95% of the variation seen in normal adult humans of both genders. The models were housed in an artificial thorax and used for in vitro testing of drug deposition from Budelin Novolizer DPIs using a breath simulator to mimic inhalation profiles reported in clinical trials of deposition from the same inhaler. Testing in the model triplet produced results for in vitro total lung deposition (TLD) consistent with the complete range of drug deposition results reported in vivo. The effect of variables such as in vitro flow rate were also predictive of in vivo deposition. To further assess the method’s robustness, in vitro drug deposition from 5 marketed DPIs was assessed in the “medium” MT-TB model. With the exception of Relenza Diskhaler, mean values for %TLD+SD differed by only \u3c 2% from their literature in vivo. The relationship between inhaler orientation and in vitro regional airway deposition was determined. Aerosol drug deposition was found to depend on the angle at which an inhaler is inserted into the mouth although the results for MT deposition were dependent on both the product and the formulation being delivered. In the clinic, inhalation profiles were collected from 20 healthy inhaler naïve volunteers (10M, 10F) before and after they received formal inhalation training in the use of a DPI. Statistically significant improvements in Peak Inhalation Flow Rate (PIFR) and Inhalation Volume (V) were observed following formalized training. The shapes of the average inhalation profiles recorded in the clinic were found to be comparable to the simulated profiles used in the in vitro deposition studies described above. In conclusion, novel in vitro test methods are described that accurately predict both the average and range of aerosol airway drug deposition seen from DPIs in the clinic
CFD Simulation of Flow through Packed Beds using the Finite Volume Technique
When a disordered packed bed, or any heterogeneous media is studied
using computational fluid dynamics, the tortuous task of generating a
domain and creating a workable mesh presents a challenging issue to
Engineers and Scientists. In this Thesis these challenges are addressed
in the form of three studies in which both traditional and novel techniques
are used to generate packed beds of spheres and cylinders for
analysis using computational fluid dynamics, more specifically, the finite
volume method. The first study uses a Monte-Carlo method to
generate random particle locations for use with a traditional CADbased
meshing approach. Computational studies are performed and
compared in detail with experimental equivalent beds. In the second
study, where there is a need for actual, physical beds to be studied,
magnetic-resonance-imaging is used coupled with a novel approach
known as image based meshing. In parallel experimental studies are
performed on the experimental bed and compared with computational
data. In the third study, to overcome fidelity issues with the previous
approaches, a physical packed bed is manufactured which is
100% geometrically faithful to its computational counterpart to provide
a direct comparison. All three computational studies have shown
promising results in comparison with the experimental data described
in this Thesis, with the data of Reichelt (1972) and the semi-empirical
correlation of Eisfeld & Schnitzlein (2001). All experiments and computational
models were carried out by the author unless otherwise
stated
Applications and Experiences of Quality Control
The rich palette of topics set out in this book provides a sufficiently broad overview of the developments in the field of quality control. By providing detailed information on various aspects of quality control, this book can serve as a basis for starting interdisciplinary cooperation, which has increasingly become an integral part of scientific and applied research