This study evaluates the impact of excluding various regions of the upper respiratory system on particle depositions in lower airways. Three types of models were investigated, Type 1 includes nasal cavity, pharyngeal regions, trachea, and lower generations, Type 2 includes pharyngeal regions, trachea and lower generations, and finally Type 3 includes just the trachea and lower generations. Results indicate increased mean velocity, turbulent kinetic energy, and wall shear stress in hypopharynx and trachea regions for Types 1 and 2 models. There are strong secondary flows within the trachea just before the lower generations in these models, moving high velocity toward the wall regions, resulting in large velocity gradients and thus increased wall shear stress. For Type 3 model, only a small region experiences high velocity secondary flow and its distribution is significantly different than those of Type 1 and 2. Although total particle depositions differ between models, results show that for fine particles, the deposition ratios in lower airways are nearly the same.

Cardiovascular stents are currently being used for intraluminal stenting of the trachea for tracheomalacia treatment. These devices composed of permanent materials are controversial due to their limitations at internal reinforcement and biocompatibility, especially in pediatrics. We show in a pediatric tracheomalacia rabbit model, a poly-L-lactic acid (PLLA) Double Opposed Helical bioresorbable stent (DH) elicits a more mild inflammatory response in the malacic airway compared to a control metal stent. To further improve efficacy, a multi-drug delivery, bioresorbable coating was designed. The coating design controllably delivers ciprofloxacin (antibiotic) for one week and dexamethasone (anti-inflammatory agent) for three months. The bioresorbable polymeric components also demonstrate feasible visibility utilizing Magnetic Resonance Imaging (MRI). The local multi-drug delivery and imaging capabilities in this coating design in combination with the bioresorbable DH stent will result in a successful intervention specifically design for pediatric tracheomalacia. This design will eliminate long-term risks associated with current permanent devices and provide necessary theranostic agents to facilitate healing and monitor progress via non-invasive imaging techniques.

Mechanical ventilation is the process of providing artificial breathing support to a patient. More than half of critically ill patients require mechanical ventilation[1]. Though mechanical ventilation increases time for recuperation, it is known to have given rise to complications arising from over-distention of lungs leading to ventilator associated lung injury (VALI) and ventilator induced lung injury (VILI). This paper aims to develop a sensor to identify breathing efforts initiated by the patient and give back responses to the ventilator to regulate ventilation modes and tidal volumes delivered by the ventilator. This will significantly aid in reducing asynchrony between the patient efforts and the ventilator input, thus preventing lung injury. Towards this end, we have simulated and studied the effect of different kinds of dynamic loading and diaphragm membrane thickness of the sensor on its sensitivity on a basic design.

The existence of obstructions such as tracheal stenosis has major impacts on respiratory functions. Therapeutic effectiveness of inhaled medications is influenced by tracheal stenosis, and particle transport and deposition pattern are modified. The majority of studies have focused on obstructions in branches of the airways, where the flow is diverted to the other branches to meet the needed oxygen intake. In this study we have investigated the effects of trachea with and without stenosis/obstruction on particle depositions and air flow in a human respiratory system. Patient specific CFD simulations were conducted; CT-scans of a patient with tracheal stenosis were used to create 3D models of bronchial tree up to 8 generations. The section of the stenosis was manually modified to create a healthy trachea. Comparisons between CFD simulations before and after intervention demonstrate the impact of the stenosis on flow characteristics and particles distribution. The numerical investigations were performed using the implicit Unsteady Reynolds-Averaged Navier-Stokes equation (U-RANS), using the commercially available software (STAR-CCM+) from CD-Adapco, along with K-ω; shear stress transport model. Two sets of CT-images of inhalation and exhalation were used for assigning Patient-specific boundary conditions at the outlets. Lagrangian Phase model was used to simulate particle transport and depositions of 10, 5 and 2.5 micron diameter particles. Results of the particle depositions for 10 micron particles highlight the difference in depositions and ultimately inhaled medications in patients with and without tracheal stenosis. Particle deposition for normal Tidal volume increased due to stenosis from 47% to 51% for 10 Micron particles and not a significant change for the 2.5 Micron particles (from 4.5% to 4.7%). Comparisons of pressure drop in each generation between patient with tracheal stenosis and the healthy lung showed significant increase in pressure drop after the stenosis, which were experienced in all generations downstream. Experimental validation of the CFD results were made with a model of healthy trachea up to 3rd generation, manufactured using Additive Layer Manufacturing (ALM) from CT-images and pressure results were compared with the corresponding CFD results. Good agreements were found.

The purpose of this study is to apply the computational fluid dynamics (CFD) technique to evaluate the tracheal airway pressure change before and after the vascular ring surgery (VRS) based on patient computed tomography (CT) images. Computer simulation results also show that after a surgical treatment the pressure drop in the tracheal airway was significantly decreased, especially for low inspiratory and expiratory velocities. In other words, the flow resistance in the tracheal airway becomes decreased after the VRS when the airway is expanded. The airway flow resistance of tracheal stenosis caused by CVR can be augmented by increased air flow velocity. Numerical results show that the pressure drop in the tracheal airway was 0.1099 Pa for the inlet inspiratory velocity of 10 cm/s before the VRS. After the VRS, the pressure drop was reduced and became 0.0598 Pa. In the meantime, the improvement gain was 45.58%. In word words, the pressure drop was reduced after the vascular ring surgery. Therefore, the CFD approach can be a useful method for quantifying the change of airway resistance and evaluating the effectiveness of relief of tracheal stenosis by the VRS.

Understanding pressure wave propagation in the lung is of importance for a number of medical devices including those for diagnostics and treatments. The main objective of this research is to quantify the transmitability of the airway tree with respect to pressure oscillations. Ovine lungs are casted to produce a hollow airway tree. Variable pressure oscillations and airflow are supplied at the trachea of the casted model and pressure oscillations are measured at the bronchioles. The study indicates that pressure waves with different frequencies can be delivered to different locations of the lung by controlling the pressure oscillation source to the lung.

Current asthma treatments using anti-inflammatory agents and airway smooth muscle (ASM) relaxants are expensive, variable in effectiveness and are associated with several cardiovascular side effects. Previous in vitro experiments conducted on ASM tissues suggest that oscillations applied to contracted muscle result in a reduction in the contractile ability of the tissue. This study focuses on investigating the combined effects of muscle relaxants (bronchodilators) and length oscillations on the dynamics of contracted ASM. Isolated porcine tracheal smooth muscle tissues are contracted using Acetylcholine. Isoproterenol (Iso), a β-agonist, is used as a bronchodilator to relax the contracted ASM. Our results suggest that the combined effect of Iso and breathing oscillations is noted to be greater than the added effects of Iso and breathing alone. It can be proposed that breathing oscillations aid the relaxation of ASM by Isoproterenol.

During human voice production, air forced from the lungs through the larynx induces vibration of the vocal folds. Computational models of this coupled fluid-solid system have traditionally utilized an incompressible fluid domain. However, studies have shown that coupling of tracheal acoustics with vocal fold dynamics is significant. Further, in the absence of compressibility, some models fail to achieve self-sustained vibration. This presentation discusses a slightly compressible airflow model, fully coupled with a vocal fold tissue model, as a possible substitute for the traditional incompressible approach. The derivation and justification of the slightly compressible fluid model are discussed. Results are reported of a study of the nature of the coupling between the fluid and vocal fold regions for both slightly compressible and incompressible fluid domains using a commercial fluid-solid finite element package. Three different types of inlet boundary conditions, including constant pressure, constant velocity, and moving wall, are explored. The incompressible and slightly compressible models with the three boundary conditions are compared with each other and with experimental data obtained using synthetic self-oscillating vocal fold models. The results are used to validate the slightly compressible flow model as well as to explore candidate boundary conditions for vocal fold vibration simulations.

Photodynamic therapy (PDT) is an FDA approved, effective, and minimally invasive cancer treatment modality with few side effects. Optimization of the PDT protocol for individual patient requires good therapeutic selectivity and high efficacy. This is possible only by enabling continuous monitoring of treating area of each patient for essential components for PDT. Two most essential components of PDT are photosensitizing agents and molecular oxygen. Currently the PDT is rather a blind process since there are no proper methods to monitor the tumor blood oxygen level and photosensitizer concentration during the treatment. In this paper we present an optical technique to monitor the tumor oxygen level and photosensitizer concentration. The technique investigated in this paper is a reflection optical technique designed with tiny semiconductor lasers and a silicon photodiode. The measurement of blood oxygen level with optical technique is not an uncommon method, but conventional transmission technique cannot be applied to the internal organs such as esophagus, trachea, and intestine. The light used in the monitoring system comes from three semiconductor diode lasers of 630nm, 650 nm and 940 nm wavelengths. Three lasers and the photodiode are mounted on to a small package to be able to imprint on to the balloon catheter that the PDT light delivery system is carrying in case of body cavities. Lasers and the photodiode are powered and controlled by the control box that is connected with a tinny cable. Light sources and respective photodiode output is controlled by the LabVIEW virtual instrumentation. The sequential on and off of light source and respective reflective signal is processed with MATLAB code integrates in the LabVIEW to make automatic calculation of the corresponding light absorption by each chromophore and to show the change in oxygen level and the photosensitizer concentration in the monitoring area. The designed system is capable of monitoring change in oxygen and photosensitizer level in any part of the human body where the tinny package is possible to place.

Inhaled Pharmaceutical Aerosols (IPAs) delivery has great potential in treatment of a variety of respiratory diseases, including asthma, pulmonary diseases, and allergies. Aerosol delivery has many advantages. It delivers medication directly to where it is needed and it is effective in much lower doses than required for oral administration. Currently, there are several types of IPA delivery systems, including pressurized metered dose inhaler (pMDI), the dry powder inhaler (DPI), and the medical nebulizer. IPAs should be delivered deep into the respiratory system where the drug substance can be absorbed into blood through the capillaries via the alveoli. Researchers have proved that most aerosol particles with aerodynamic diameter of about 1–5 μm, if slowly and deeply inhaled, could be deposited in the peripheral regions that are rich in alveoli [1–3]. The purpose of this study is to investigate the effects of various inhaling rates with breath-holding pause on the aerosol deposition (Dp = 0.5–5 μm) in a human upper airway model extending from mouth to 3rd generation of trachea. The oral airway model is three dimensional and non-planar configurations. The dimensions of the model are adapted from a human cast. The air flow is assumed to be unsteady, laminar, and incompressible. The investigation is carried out by Computational Fluid Dynamics (CFD) using the software Fluent 6.2. The user-defined function (UDF) is employed to simulate the cyclic inspiratory flows for different IPA inhalation patterns. When an aerosol particle enters the mouth respiratory tract, its particles experience abrupt changes in direction. The secondary flow changes its direction as the airflow passes curvature. Intensity of the secondary flow is strong after first bend at pharynx and becomes weaker after larynx. In flow separation, a particle can be trapped and follow the eddy and deposit on the surface. Particle deposition fraction generally increases as particle size and inhaling airflow velocity increase.

The hazard caused by inhaled particles depends on the site at which they deposit within the respiratory system. Knowledge of respiratory aerosol deposition rates and locations is necessary to (1) evaluate potential health effects and establish critical exposure limits and (2) design effective inhaled medications that target specific lung regions. Particles smaller than 10 μm in diameter can be breathed into lungs and are known as inhalable particles, while most of larger particles settle in mouth and nose. Inhalable particles settle in different regions of the lungs and the settling regions depends on the particle size. The motion of a particle is mainly affected by the inertia of the particle and by the particle’s aerodynamic drag. The most important dimensionless parameters in the prediction of particle motion are the flow Reynolds number and the Stoke number, which combines the effects of particle diameter, particle density, shape factor and slip factor. The purpose of this study is to investigate the airflows in human respiratory airways. The influence of particle size on transport and deposition patterns in the 3-D lung model of the human airways is the primary concern of this research. The lung model developed for this research extends from the trachea to the segmental bronchi and it is based on Weibel’s model. The velocity field of air is studied and particle transport and deposition are compared for particles in the diameter range of 1 μm – 100 μm (G0 to G2) and 0.1 μm – 10 μm (G3 to G5) at airflow rates of 6.0, 16.7, and 30.0 L/min, which represent breathing at rest, light activity, and heavy activity, respectively. The investigation is carried out by computational fluid dynamics (CFD) using the software Fluent 6.2. Three-dimensional, steady, incompressible, laminar flow is simulated to obtain the flow field. The discrete phase model (DPM) is then employed to predict the particle trajectories and the deposition efficiency by considering drag and gravity forces. In the present study, the Reynolds number in the range of 200 – 2000 and the Stoke number in the range of 10 −5 – 0.12 are investigated. For particle size over 10 μm, deposition mainly occurs by inertial impaction, where deposition generally increases with increases in particle size and flow rate. Most of the larger micron sized particles are captured at the bifurcations, while submicron sized particles flow with the fluid into the lung lower airways. The trajectories of submicron sized particles are strongly influenced by the secondary flow in daughter branches. The present results of particle deposition efficiency in the human upper airways compared well with data in the literature.

In recent years, mild or moderate hypothermia during which brain temperature is reduced to 30–35°C has been proposed for clinical use as an adjunct for achieving protection from cerebral ischemia and traumatic brain injury. There are two approaches for achieving a reduction in brain temperature. One is via systemic hypothermia where the whole body is cooled. This approach may produce deleterious systemic complications and require intensive monitoring. Another approach is called selective brain cooling (SBC) in which the brain is selectively cooled while the rest of the body is kept at normal temperature. Clinically feasible SBC protocols include head hood or helmet with water or chemical cooling, head immersion in iced water, nasophyaryngeal cooling after tracheal intubation, and intro-carotid flushing. Simply packing ice or wearing cooling helmet is easy to implement. Previous theoretical study [Zhu and Diao, 2001] suggests that it is feasible to achieve mild hypothermia via head surface cooling. However, most physicians believe that it takes a much longer time to reduce the brain temperature using head surface cooling. In this study, a three-dimensional theoretical model is developed to study the transient and steady state temperature distribution in the brain during SBC. The effect of regionally varying local blood perfusion rate in the brain tissue on the temporal and spatial temperature gradient is examined. Other factors including the brain size and the thermal contact resistance between the cooling medium and the head scalp are evaluated in the simulation.

Clearance of mucus by the beating action of cilia is the primary means of removing inhaled particulates and airway debris from airways in healthy people. However many pulmonary diseases are associated with impaired mucociliary clearance mechanisms. For these patients, cough is the default airway clearance mechanism. Unfortunately most pulmonary disease patients can only produce low expiratory flow rates and have difficulty coughing for this reason.

The objectives of the present study are to investigate the response of a tracheal smooth muscle tissue to an applied longitudinal vibration following isotonic shortening, and, using experimental data, to simulate the mechanical response through a non-linear finite element analysis. The response of an activated smooth muscle tissue to forced length oscillations at 33Hz for 1 second was obtained. The response in terms of stiffness change and hysteresis was estimated from the experimental data. A finite element simulation was carried out to simulate the vibratory response under experimental conditions. The results obtained indicate that the approach and the vibratory response obtained may be useful for describing the cross-bridge deattachements within the cells as well as connective tissue connections characteristics of tracheal smooth muscle tissue.

The flow through a compliant-walled channel or tube is analogous to human systems, such as blood vessels (Holt, 1969), the trachea during forced expiration (Elad and Kamm, 1989), and, with some limitations, the glottis (Conrad, 1980). Typical studies involving collapsible channels have used a rigid channel with a longitudinal section of the channel wall replaced with a deformable structure, such as a membrane. Numerical and analytical studies of the flow and accompanying wall deformation have used 1-dimensional or lumped-parameter models (e.g., Shapiro, 1977; Cancelli and Pedley, 1985) as well as detailed flow and structural models using the finite element method (e.g., Rast, 1994; Luo and Pedley, 1995, 1996; Shim and Kamm, 2002; Cai and Luo, 2003).

The vibration characteristics of a branched thin circular cylindrical shell structure, which resembles the respiratory system tree, are determined using membrane shell theory. Since there is no previous published data in this regard, the finite element method is used to justify the analytical results. The human airways are of a simple tree pattern but complex in physical structure. However, they should behave just like most mechanical parts that have their own natural frequencies in response to external excitation. Investigations are performed from the trachea down to the sixteenth generation. There is a good agreement between the two approaches, which set good foundations for future research.

The cell alignment in a smooth muscle tissue plays a significant role in determining its mechanical properties. In addition to shortening strain, the off-axis cell orientation θ also modify the shear stress relationship significantly. A simulation model based on finite element analysis is developed to study the effect of stresses of tracheal smooth muscle tissue when its cells are orientated off-axially. Results obtained indicate that the maximum shear stress values of tracheal smooth muscle tissue at 45% strain are 2.5 times the values at 20% strain for all three off-axis orientation values θ = 15°, 30° and 45°.

Incorporating the properties of the surrounding medium, the low frequency characteristics of the trachea-bronchia are determined using a relatively accurate Finite Element Model (FEM). Focus is made on the effect of the branching angle and the embedding surroundings on these characteristics. It is concluded that the natural frequencies are significantly influenced by the surrounding medium elastance and are insignificantly affected by the branching angle within realistic values (30, 45 60 degree in plane and 45 degree in plane plus 45 degree out of plane branching angles investigated).

An experimental and theoretical investigation is conducted to study the dynamic response of a tracheal smooth muscle under isometric conditions. The stiffness variation due to external vibration is investigated experimentally using trachea smooth muscles from excised pigs. The finite element method is used to model the muscle as a 2-D strip with variable stiffness and subjected to an external excitation. The Cauchy’s first law is invoked to describe the motion and Galerkin’s method is used to develop the finite element formulation. Different boundary conditions are considered to simulate the vibration characteristics and to get realistic compatibility with actual muscle conditions. The model predicts the stiffness variation due to vibration that is observed experimentally. The main outcome from this investigation is the fact that smooth muscle contractions could be relaxed by tuning the excitation within predetermined frequencies.

Three non-destructive testing techniques are developed and investigated to determine the Young’s modulus of elasticity of the trachea and the results are compared with the standard uniaxial state of stress method. These techniques are based on: (1) simulating the trachea as a pressurized vessel and deducing a special relationship between the pressure and the radial strain; (2) using two hydrophones and determining the variation in acoustic transmittance caused by the presence of the trachea in a propagation path within a water-bath; (3) considering the trachea as a thin cylindrical shell and determining the resonance radial vibration response. Discussion is presented to identify the “pros” and “cons” of each technique and final practical recommendations are made.