Numerical simulation of air flow and medical-aerosol distribution in an innovative nebulizer hood

Meandered and muddled: a systematic review on the impact of air pollution on ocular health

From the years 1970-2023, a systematic overview of the diverse consequences of particulate matter on eye health and a disease classification according to acute, chronic, and genetic are presented using the PubMed, Research Gate, Google Scholar, and Science Direct databases. Various studies on medical aspects correlate with the eye and health. However, from an application perspective, there is limited research on the ocular surface and air pollution. The main objective of the study is to uncover the relationship between eye health and air pollution, particularly particulate matter, along with other external factors acting as aggravators. The secondary goal of the work is to examine the existing models for mimicking human eyes. The study is followed by a questionnaire survey in a workshop, in which the exposure-based investigation was tagged based on their activity. This paper establishes a relationship between particulate matter and its influence on human health, leading to numerous eye diseases like dry eyes, conjunctivitis, myopia, glaucoma, and trachoma. The results of the questionnaire survey indicate that about 68% of the people working in the workshop are symptomatic with tears, blurred vision, and mood swings, while 32% of the people were asymptomatic. Although there are approaches for conducting experiments, the evaluation is not well defined; empirical and numerical solutions for particle deposition on the eye are needed. There prevails a broad gap in the arena of ocular deposition modeling.

Reconciling Oxygen and Aerosol Delivery with a Hood on In Vitro Infant and Paediatric Models

This study aimed to evaluate optimal aerosol and oxygen delivery with a hood on an infant model and a paediatric model. A facemask and a hood with three inlets, with or without a front cover, were used. A small-volume nebuliser with a unit-dose of salbutamol was used for drug delivery and an air entrainment nebuliser was used to deliver oxygen at 35%. Infant and paediatric breathing patterns were mimicked; a bacterial filter was connected to the end of a manikin trachea for aerosol drug collection, and an oxygen analyser was used to measure the oxygen concentration. For the infant model, inhaled drug dose was significantly higher when the nebuliser was placed in the back of the hood and with a front cover. This was verified by complementary computational simulations in a comparable infant-hood model. For the paediatric model, the inhaled dose was greater with a facemask than with a hood. Oxygen delivery with a facemask and a hood with a front cover achieved a set concentration in both models, yet a hood without a front cover delivered oxygen at far lower concentrations than the set concentration.

Pediatric in vitro and in silico models of deposition via oral and nasal inhalation

Respiratory tract deposition models provide a useful method for optimizing the design and administration of inhaled pharmaceutical aerosols, and can be useful for estimating exposure risks to inhaled particulate matter. As aerosol must first pass through the extrathoracic region prior to reaching the lungs, deposition in this region plays an important role in both cases. Compared to adults, much less extrathoracic deposition data are available with pediatric subjects. Recently, progress in magnetic resonance imaging and computed tomography scans to develop pediatric extrathoracic airway replicas has facilitated addressing this issue. Indeed, the use of realistic replicas for benchtop inhaler testing is now relatively common during the development and in vitro evaluation of pediatric respiratory drug delivery devices. Recently, in vitro empirical modeling studies using a moderate number of these realistic replicas have related airway geometry, particle size, fluid properties, and flow rate to extrathoracic deposition. Idealized geometries provide a standardized platform for inhaler testing and exposure risk assessment and have been designed to mimic average in vitro deposition in infants and children by replicating representative average geometrical dimensions. In silico mathematical models have used morphometric data and aerosol physics to illustrate the relative importance of different deposition mechanisms on respiratory tract deposition. Computational fluid dynamics simulations allow for the quantification of local deposition patterns and an in-depth examination of aerosol behavior in the respiratory tract. Recent studies have used both in vitro and in silico deposition measurements in realistic pediatric airway geometries to some success. This article reviews the current understanding of pediatric in vitro and in silico deposition modeling via oral and nasal inhalation.

Drug-targeting methodologies with applications: A review

Targeted drug delivery to solid tumors is a very active research area, focusing mainly on improved drug formulation and associated best delivery methods/devices. Drug-targeting has the potential to greatly improve drug-delivery efficacy, reduce side effects, and lower the treatment costs. However, the vast majority of drug-targeting studies assume that the drug-particles are already at the target site or at least in its direct vicinity. In this review, drug-delivery methodologies, drug types and drug-delivery devices are discussed with examples in two major application areas: (1) inhaled drug-aerosol delivery into human lung-airways; and (2) intravascular drug-delivery for solid tumor targeting. The major problem addressed is how to deliver efficiently the drug-particles from the entry/infusion point to the target site. So far, most experimental results are based on animal studies. Concerning pulmonary drug delivery, the focus is on the pros and cons of three inhaler types, i.e., pressurized metered dose inhaler, dry powder inhaler and nebulizer, in addition to drug-aerosol formulations. Computational fluid-particle dynamics techniques and the underlying methodology for a smart inhaler system are discussed as well. Concerning intravascular drug-delivery for solid tumor targeting, passive and active targeting are reviewed as well as direct drug-targeting, using optimal delivery of radioactive microspheres to liver tumors as an example. The review concludes with suggestions for future work, considereing both pulmonary drug targeting and direct drug delivery to solid tumors in the vascular system.

Hood nebulization: effects of head direction and breathing mode on particle inhalability and deposition in a 7-month-old infant model

BACKGROUND

Aerosol drug delivery to infants is a strong function of their behavior. Infants can be active during medication administration, changing head position or breathing mode. The objective was to evaluate the influence of the head direction and breathing mode on the hood drug delivery in a 7-month-old girl airway model by using an approach that couples imaging with computational fluid dynamics (CFD). Three head directions, i.e., face up, face side, and sitting (face front), and two breathing modes, i.e., oronasal and nasal breathing, were studied.

METHODS

The face-airway model was developed from computed tomography scans of a 7-month-old girl. Respiratory airflows and particle transport were simulated with the low Reynolds number κ-ω turbulence model and Lagrangian tracking approach. Three pharmaceutical aerosol sizes (1, 2.5, and 5 μm) via hood nebulization were considered under quiet breathing conditions (5 L/min).

RESULTS

Both head direction and breathing mode can noticeably affect aerosol inhalability and lung delivery efficiency. A maximum of 20% difference in inhalability is observed among the three head positions. Facial-ocular depositions are predominantly influenced by head position, but not breathing mode. The facial-ocular deposition rate with the face-up position is about threefold that with the sitting position for 5-μm particles. Nasal breathing gives about 17.8% lower lung deposition and about 65% higher facial-ocular deposition than the oronasal breathing.

CONCLUSION

The face-side position has less facial-ocular deposition than the face-up position, while still achieving similar lung delivery efficiency. Because aerosols deposited around the eyes may cause irritation to the eyes, the face-side position appears to be a better option than the face-up position for comfort and safety reasons.

The use of computational fluid dynamics in inhaler design

INTRODUCTION

Computational fluid dynamics (CFD) has recently seen increased use in the design of pharmaceutical inhalers. The use of CFD in the design of inhalers is made difficult by the complex nature of aerosol generation. At present, CFD has provided valuable insight into certain aspects of inhaler performance, though limitations in computational power have prevented the full implementation of numerical methods in the design of inhalers.

AREAS COVERED

This review examines the application of CFD in the design of aerosol drug delivery technologies with a focus on pressurized metered-dose inhalers (pMDI), nebulizers and dry powder inhalers (DPIs). Challenges associated with the application of CFD in inhaler design are discussed along with relevant investigations in the literature. Discussions of discrete element modeling (DEM) and the simulation of pharmaceutical aerosol dispersion are included.

EXPERT OPINION

The extreme complexity of coupled fluid and aerosol dynamics associated with aerosol generation has somewhat limited the use of CFD in inhaler design. Combined CFD--DEM simulations provide a useful tool in the design of DPIs, though aerosol generation in pMDIs and nebulizers has eluded CFD modeling. The most beneficial use of CFD typically occurs when concurrent CFD and experimental analyses are performed, significantly enhancing the knowledge provided by experiment alone.

The use of computational approaches in inhaler development

Computational Fluid Dynamics (CFD) and Discrete Element Modelling (DEM) studies relevant to inhaled drug delivery are reviewed. CFD is widely used in device design to determine airflow patterns and turbulence levels. CFD is also used to simulate particles and droplets, which are subjected to various forces, turbulence and wall interactions. These studies can now be performed routinely because of the availability of commercial software containing high quality turbulence and particle models. DEM allows for the modelling of agglomerate break-up upon interaction with a wall or due to shear in the flow. However, the computational cost is high and the number of particles that can be simulated is minimal compared with the number present in typical inhaled formulations. Therefore DEM is currently limited to fundamental studies of break-up mechanisms. With decreasing computational limitations, simulations combining CFD and DEM that can address outstanding issues in agglomerate break-up and dispersion will be possible.

Numerical investigation of aerosol deposition at the eyes when using a hood inhaler for infants--a 3D simulation

A numerical investigation of a hood inhaler is presented, aiming at the assessment of the amount of aerosol that reaches the eyes of the patient when administering medications with such a device. Using a hood for aerosol therapy for infants was already found to be effective and friendly to handle over the commonly used face mask. Using a hood device may adversely deliver unwanted medications to the eyes of the infant. The current study addresses the extent of aerosol deposition at the infant's eye zone. We describe the development and utilization of a numerical simulation for studying the transport and fate of the aerosol particles within a 3D realistic representation of the hood and the infant's head, with a focus on the eye zone. The governing equations were solved using the commercial software, FLUENT 6.1, which is based on the finite volume method. The computational domain was created using the GAMBIT package. The computational geometry was built separately for each configuration of the hood and the infant. It is shown that under optimal working conditions (i.e., when the infant's head is aligned to the funnel) the percentage of aerosol reaching the eye zone is 0.48%. However, when the funnel is tilted toward the eyes the amount of aerosol reaching the eyes zone is predicted to be 4.7%. In general, the results obtained in this study are in good agreement with available in vitro data. It can be concluded that using the hood for aerosol therapy results in minimal deposition at the infant's eye area.

Modeling of aerosol deposition with interface devices

Various approaches can be used to mathematically model the performance of different masks, mouthpieces, and aerosol delivery devices. The sophistication of such models can vary widely, from the use of simple algebraic empirical correlations to advanced computational fluid dynamics simulations. Bench-top testing is also often used to model aspects of devices, since it is difficult to capture certain aspects of device behavior with mathematical models. These various approaches to modeling differ in their limitations. Empirical correlations exist for predicting the effects of varying mouthpiece diameter and mouth-throat dimensions on extrathoracic losses, but are restricted to stable, nonballistic aerosols in certain flow rate ranges. Computational fluid dynamics (CFD) simulations that solve the Reynolds-averaged Navier-Stokes (RANS) equations typically require near-wall turbulence corrections in order to adequately model mouth-throat deposition, while Large Eddy Simulation (LES) removes this deficiency. Bench-top models that use replicas of the extrathoracic airways vary in their accuracy and generality in replicating the filtering properties of these airways. Choosing and using these various modeling approaches for evaluating patient-device interfaces requires knowledge of their merits and pitfalls, a brief discussion of which is given here.

Administration of aerosolized drugs to infants by a hood: a three-dimensional numerical study

Using a hood for aerosol delivery to infants was found to be effective and user-friendly compared to the commonly used face mask. The currently available hood design has an even greater potential in terms of efficiency, and a numerical simulation can serve as a tool for its optimization. The present study describes the development and utilization of a numerical simulation for studying the transport and fate of the aerosol particles and the carrier gas within a three-dimensional realistic representation of the hood and the infant's head. The study further incorporates realistic breathing patterns, with a longer expiration phase than an inspiration phase. Both nose and mouth breathing are simulated. While the base case assumes that the funnel that delivers the aerosol within the hood is perpendicular to the infant's face, more realistic scenarios include a funnel that is slanted with respect to the infant face, the infant's head taking a general position with respect to the funnel, and the funnel and the head being both tilted. A good agreement is found between computation and experimental results. As expected, the most efficient drug delivery, 18%, is achieved when the funnel is normal to the infant's face. The quantitative evaluation of different scenarios presented in this work increases the knowledge of physicians, nurses, and parents regarding the efficacy of the treatment, in terms of the actual amount of drug inhaled under various modes of function of the device.