Inertial deposition effects: a study of aerosol mechanics in the trachea using laser Doppler velocimetry and fluorescent dye

Enhanced Optimal Parameter-Based Nebulizer Design for Flow Analysis of Fluticasone Propionate

A jet nebulizer sprays a fine mist or aerosol directly into the lungs to reduce inflammation, expand airways, and make breathing easier for respiratory patients. Asthma, COPD, emphysema, and cystic fibrosis are treated with jet nebulizers. They are chosen over other nebulizers for their shorter treatment time and wider medication compatibility. For mechanically ventilated patients, jet nebulizers humidify oxygen to provide bronchodilators, antibiotics, and other respiratory medications. Additionally, they treat pneumonia, bronchitis, and other lung infections. Aerosol therapy requires medical jet nebulizers. However, experiment setup is time-consuming and challenging to enhance smaller droplet output. The study is aimed at enhancing the nebulizer and process parameters using numerical simulation and comparing the results to experimental data from the Malvern Spraytec™ laser diffraction system. This numerical model improves nebulization knowledge and predicts process parameters that affect output. Ansys Fluent was used to analyze a Creo-designed jet nebulizer solid model. The Spraytec™ experimental method was utilized to characterize fluticasone propionate's aerosol output and build the best nebulizer. Laser diffraction and computational fluid dynamics (CFD) analysis measured the nebulizer aerosol output. Comparing particle size data between 2 and 5 μm. The results are similar, with a difference of 4.20%. Taguchi optimization found the optimal process parameter, and a conformation test enhanced the process parameter. The nebulizer generates 8.57% more fluticasone propionate at optimal particle size. The optimized nebulizer generates aerosols reliably and speeds up patient recovery.

Radiation Dosimetry of Inhaled Radioactive Aerosols: CFPD and MCNP Transport Simulations of Radionuclides in the Lung

Despite extensive efforts in studying radioactive aerosols, including the transmission of radionuclides in different chemical matrices throughout the body, the internal organ-specific radiation dose due to inhaled radioactive aerosols has largely relied on experimental deposition data and simplified human phantoms. Computational fluid-particle dynamics (CFPD) has proven to be a reliable tool in characterizing aerosol transport in the upper airways, while Monte Carlo based radiation codes allow accurate simulation of radiation transport. The objective of this study is to numerically assess the radiation dosimetry due to particles decaying in the respiratory tract from environmental radioactive exposures by coupling CFPD with Monte Carlo N-Particle code, version 6 (MCNP6). A physiologically realistic mouth-lung model extending to the bifurcation generation G9 was used to simulate airflow and particle transport within the respiratory tract. Polydisperse aerosols with different distributions were considered, and deposition distribution of the inhaled aerosols on the internal airway walls was quantified. The deposition mapping of radioactive aerosols was then registered to the respiratory tract of an image-based whole-body adult male model (VIP-Man) to simulate radiation transport and energy deposition. Computer codes were developed for geometry visualization, spatial normalization, and source card definition in MCNP6. Spatial distributions of internal radiation dosimetry were compared for different radionuclides (¹³¹I, ^134,137Cs, ⁹⁰Sr-⁹⁰Y, ¹⁰³Ru and ^239,240Pu) in terms of the radiation fluence, energy deposition density, and dose per decay.

Experimental and numerical investigation on inspiration and expiration flows in a three-generation human lung airway model at two flow rates

The respiration flow pattern plays a key role in fluid flow, heat and mass transfer in human lung airway. To reveal the complex flow pattern within human lung multiple-generation airway, both the steady inspiration and expiration flows are comprehensively studied using laser Doppler velocimetry technique and computational fluid dynamics method for an idealized human tracheobronchial three-generation airway model at two flow rates, corresponding to an adult male breathing under light activity and moderate exercise conditions, respectively. The comparison of mainstream velocity between the measurements and simulations are generally good. Both of the inspiration and expiration flows are heavily influenced by the combination of geometrical bifurcating/merging, local wall curvature, limited generation length and multi-generation interaction. The mainstream flow is non-uniform and behaves as skewed, double-peaked and M-shaped patterns. The secondary flow is complex and characteristic of Dean-type two-vortex, four-vortex, six-vortex and eight-vortex patterns. This work is of scientific significance for a deep understanding of respiratory flow physics and of certain application values for clinical diagnosis and remedy of respiratory deceases.

Supraglottic Atomization of Surfactant in Spontaneously Breathing Lambs Receiving Continuous Positive Airway Pressure

OBJECTIVES

To determine the short-term tolerance, efficacy, and lung deposition of supraglottic atomized surfactant in spontaneously breathing lambs receiving continuous positive airway pressure.

DESIGN

Prospective, randomized animal study.

SETTING

Animal research laboratory.

SUBJECTS

Twenty-two preterm lambs on continuous positive airway pressure (132 ± 1 d gestational age).

INTERVENTIONS

Animals receiving continuous positive airway pressure via binasal prongs at 8 cm H2O were randomized to receive atomized surfactant at approximately 60-minute of life (atom; n = 15) or not (control; n = 7). The atom group received 200 mg/kg of poractant alfa (Curosurf; Chiesi Farmaceutici SpA, Parma, Italy) over 45 minutes via a novel atomizer located in the upper pharynx that synchronized surfactant delivery with the inspiratory phase.

MEASUREMENTS AND MAIN RESULTS

Arterial blood gas, regional distribution of tidal ventilation (electrical impedance tomography), and carotid blood flow were recorded every 15 minutes until 90 minutes after stabilizing on continuous positive airway pressure. Gas exchange, respiratory rate, and hemodynamic variables, including carotid blood flow, remained stable during surfactant treatment. There was a significant improvement in arterial alveolar ratio after surfactant delivery in the atom group (p < 0.05; Sidak posttests), while there was no difference in PaCO2. Electrical impedance tomography data showed a more uniform pattern of ventilation in the atom group. In the atom group, the median (interquartile range) deposition of surfactant in the lung was 32% (22-43%) of the delivered dose, with an even distribution between the right and the left lungs.

CONCLUSIONS

In our model of spontaneously breathing lambs receiving CPAP, supraglottic atomization of Curosurf via a novel device was safe, improved oxygenation and ventilation homogeneity compared with CPAP only, and provided a relatively large lung deposition suggesting clinical utility.

Superiority of nebulized corticosteroids over dry powder inhalers in certain patients with cough variant asthma or cough-predominant asthma

BACKGROUND

The particle distribution might differ between nebulizer therapy and metered-dose inhaler (MDI) or dry powder inhaler (DPI) therapy because the particles repeatedly enter/re-enter the airways with the nebulizer. Inhaled corticosteroids (ICS) were administered with a nebulizer to assess the benefit of changes in the distribution of particles in patients with cough variant asthma (CVA) and cough-predominant asthma (CPA).

METHODS

Patients whose symptoms were not controlled by their current therapy were enrolled. In patients receiving high-dose ICS by MDI or DPI (ICS-MDI/DPI), steroid therapy was switched to 1,320μg/day of nebulized dexamethasone (1,600μg as dexamethasone sodium phosphate) (chronic steroid-independent group). In patients receiving systemic steroids regardless of their ICS-MDI/DPI therapy, nebulized dexamethasone was added and any concurrent ICS-MDI/DPI therapy was halted to detect a steroid-sparing effect (chronic steroid-dependent group). In patients with acute exacerbation of CVA or CPA and persistent symptoms despite systemic corticosteroids, nebulized dexamethasone was added to assess its effect (acute group).

RESULTS

Superior symptom control was achieved in 10 out of 12 steroid-independent patients, 3 out of 6 steroid-dependent patients, and all 7 acute patients.

CONCLUSIONS

Delivery of ICS via a nebulizer has advantages over ICS-MDI/DPI in some patients with CVA or CPA.

Development of a realistic human airway model

Numerous models of human lungs with various levels of idealization have been reported in the literature; consequently, results acquired using these models are difficult to compare to in vivo measurements. We have developed a set of model components based on realistic geometries, which permits the analysis of the effects of subsequent model simplification. A realistic digital upper airway geometry except for the lack of an oral cavity has been created which proved suitable both for computational fluid dynamics (CFD) simulations and for the fabrication of physical models. Subsequently, an oral cavity was added to the tracheobronchial geometry. The airway geometry including the oral cavity was adjusted to enable fabrication of a semi-realistic model. Five physical models were created based on these three digital geometries. Two optically transparent models, one with and one without the oral cavity, were constructed for flow velocity measurements, two realistic segmented models, one with and one without the oral cavity, were constructed for particle deposition measurements, and a semi-realistic model with glass cylindrical airways was developed for optical measurements of flow velocity and in situ particle size measurements. One-dimensional phase doppler anemometry measurements were made and compared to the CFD calculations for this model and good agreement was obtained.

Convective flow dominates aerosol delivery to the lung segments

Most previous computational studies on aerosol transport in models of the central airways of the human lung have focused on deposition, rather than transport of particles through these airways to the subtended lung regions. Using a model of the bronchial tree extending from the trachea to the segmental bronchi (J Appl Physiol 98: 970-980, 2005), we predicted aerosol delivery to the lung segments. Transport of 0.5- to 10-μm-diameter particles was computed at various gravity levels (0-1.6 G) during steady inspiration (100-500 ml/s). For each condition, the normalized aerosol distribution among the lung segments was compared with the normalized flow distribution by calculating the ratio (R(i)) of the number of particles exiting each segmental bronchus i to the flow. When R(i) = 1, particle transport was directly proportional to segmental flow. Flow and particle characteristics were represented by the Stokes number (Stk) in the trachea. For Stk < 0.01, R(i) values were close to 1 and were unaffected by gravity. For Stk > 0.01, R(i) varied greatly among the different outlets (R(i) = 0.30-1.93 in normal gravity for 10-μm particles at 500 ml/s) and was affected by gravity and inertia. These data suggest that, for Stk < 0.01, ventilation defines the delivery of aerosol to lung segments and that the use of aerosol tracers is a valid technique to visualize ventilation in different parts of the lung. At higher Stokes numbers, inertia, but not gravitational sedimentation, is the second major factor affecting the transport of large particles in the lung.

Effects of the laryngeal jet on nano- and microparticle transport and deposition in an approximate model of the upper tracheobronchial airways

The extent to which laryngeal-induced flow features penetrate into the upper tracheobronchial (TB) airways and their related impact on particle transport and deposition are not well understood. The objective of this study was to evaluate the effects of including the laryngeal jet on the behavior and fate of inhaled aerosols in an approximate model of the upper TB region. The upper TB model was based on a simplified numerical reproduction of a replica cast geometry used in previous in vitro deposition experiments that extended to the sixth respiratory generation along some paths. Simulations with and without an approximate larynx were performed. Particle sizes ranging from 2.5 nm to 12 mum were considered using a well-tested Lagrangian tracking model. The model larynx was observed to significantly affect flow dynamics, including a laryngeal jet skewed toward the right wall of the trachea and a significant reverse flow in the left region of the trachea. Inclusion of the laryngeal model increased the tracheal deposition of nano- and micrometer particles by factors ranging from 2 to 10 and significantly reduced deposition in the first three bronchi of the model. Considering localized conditions, inclusion of the laryngeal approximation decreased deposition at the main carina and produced a maximum in local surface deposition density in the lobar-to-segmental bifurcations (G2-G3) for both 40-nm and 4-microm aerosols. These findings corroborate previous experiments and highlight the need to include a laryngeal representation in future computational and in vitro models of the TB region.

Phase-contrast velocimetry with hyperpolarized3He for in vitro and in vivo characterization of airflow

This paper describes a technique that combines radial MRI and phase contrast (PC) to map the velocities of hyperpolarized gases ((3)He) in respiratory airways. The method was evaluated on well known geometries (straight and U-shaped pipes) before it was applied in vivo. Dynamic 2D maps of the three velocity components were obtained from a 10-mm slice with an in-plane spatial resolution of 1.6 mm within 1 s. Integration of the in vitro through-plane velocity over the slice matched the input flow within a relative precision of 6.4%. As expected for the given Reynolds number, a parabolic velocity profile was obtained in the straight pipe. In the U-shaped pipe the three velocity components were measured and compared to a fluid-dynamics simulation so the precision was evaluated as fine as 0.025 m s(-1). The technique also demonstrated its ability to visualize vortices and localize characteristic points, such as the maximum velocity and vortex-center positions. Finally, in vivo feasibility was demonstrated in the human trachea during inhalation.

Computational Simulations of Airflow in an In Vitro Model of the Pediatric Upper Airways

In order to understand mechanisms of gas and aerosol transport in the human respiratory system airflow in the upper airways of a pediatric subject (male aged 5) was calculated using Computational Fluid Dynamic techniques. An in vitro reconstruction of the subject’s anatomy was produced from MRI images. Flow fields were solved for steady inhalation at 6.4 and 8 LPM. For validation of the numerical solution, airflow in an adult cadaver based trachea was solved using identical numerical methods. Comparisons were made between experimental results and computational data of the adult model to determine solution validity. It was found that numerical simulations can provide an accurate representation of axial velocities and turbulence intensity. Data on flow resistance, axial velocities, secondary velocity vectors, and turbulent kinetic energy are presented for the pediatric case. Turbulent kinetic energy and axial velocities were heavily dependant on flow rate, whereas turbulence intensity varied less over the flow rates studied. The laryngeal jet from an adult model was compared to the laryngeal jet in the pediatric model based on Tracheal Reynolds number. The pediatric case indicated that children show axial velocities in the laryngeal jet comparable to adults, who have much higher tracheal Reynolds numbers than children due to larger characteristic dimensions. The intensity of turbulence follows a similar trend, with higher turbulent kinetic energy levels in the pediatric model than would be expected from measurements in adults at similar tracheal Reynolds numbers. There was reasonable agreement between the location of flow structures between adults and children, suggesting that an unknown length scale correlation factor could exist that would produce acceptable predictions of pediatric velocimetry based off of adult data sets. A combined scale for turbulent intensity as well may not exist due to the complex nature of turbulence production and dissipation.