Dynamic change of the upper airway during inhalation via aerosol delivery devices

Use of Airway Replicas in Lung Delivery Applications

The use of extrathoracic airway replicas in optimization of drug delivery to the lungs with nebulizers, dry powder inhalers (DPIs) and pressurized metered-dose inhalers (pMDIs) is discussed. Such airway replicas have been useful in evaluating new pulmonary drug delivery platforms mainly based on the comparison of the total lung dose (TLD) and the aerodynamic particle size distribution (APSD) of the aerosol distal to the physical models. The ability of these in vitro methods to replicate in vivo results has allowed advancements in respiratory drug delivery and in the accuracy and utility of in vitro-in vivo correlations (IVIVCs).

Aerosol drug-delivery and short-term clinical outcomes of suboptimal peak inspiratory flow rate in chronic obstructive pulmonary disease

AIM OF WORK

Suboptimal peak inspiratory flow rate (PIFR) is highly prevalent in chronic obstructive pulmonary disease (COPD) patients owing to the mismatch of their own PIFR with the corresponding inhaler-device resistance. This study aimed to evaluate aerosol drug-delivery and short-term clinical outcomes of suboptimal PIFR in COPD subjects.

METHODS

Twenty optimal and suboptimal COPD subjects were crossed over in this prospective, randomised, controlled, open-label study. They were tested for urinary salbutamol amount (USAL30) and spirometric response 30 min poststudy dose (200 µg salbutamol) through Aerolizer^® and Handihaler^® after assessment of their own PIFR through In-Check™ Dial G16. Urine samples were extracted through solid-phase extraction and assayed through a high performance liquid chromatography (HPLC) method.

RESULTS

Mean USAL30 was significantly higher in the optimal group than in the suboptimal group (P = .001). There was no significant difference in ΔFEV1% predicted and ΔFVC% predicted between optimal and suboptimal groups, with higher values in optimal Aerolizer^® and Handihaler^® than in suboptimal groups.

CONCLUSION

Suboptimal PIFR was associated with a significantly lower drug delivery in COPD subjects at hospital discharge, and a slightly lower pulmonary function response 30 min postbronchodilation if compared with optimal PIFR.

In vitro-in vivo correlations (IVIVCs) of deposition for drugs given by oral inhalation

Conventional in vitro tests to assess the aerodynamic particle size distribution (APSD) from inhaler devices use simple right-angle inlets ("mouth-throats", MTs) to cascade impactors, and air is drawn through the system at a fixed flow for a fixed time. Since this arrangement differs substantially from both human oropharyngeal airway anatomy and the patterns of air flow when patients use inhalers, the ability of in vitro tests to predict in vivo deposition of pharmaceutical aerosols has been limited. MTs that mimic the human anatomy, coupled with simulated breathing patterns, have yielded estimates of lung dose from in vitro data that closely match those from in vivo gamma scintigraphic or pharmacokinetic studies. However, different models of MTs do not always yield identical data, and selection of an anatomical MT and representative inhalation profiles remains challenging. Improved in vitro - in vivo correlations (IVIVCs) for inhaled drug products could permit increased reliance on in vitro data when developing new inhaled drug products, and could ultimately result in accelerated drug product development, together with reduced research and development spending.

Particle Size Dynamics: Toward a Better Understanding of Electronic Cigarette Aerosol Interactions With the Respiratory System

The knowledge of possible acute and long-term health effects of aerosols inhaled from electronic cigarettes (ECs) is still limited partially due to incomplete awareness of physical phenomena related to EC-aerosol dynamics. This short review discusses the basic processes of aerosol transformation (dynamics) upon inhalation, indicating also the need for the accurate determination of the size of droplets in the inhaled EC-mist. The significance of differences in the aerosol particle size distribution for the prediction of regional deposition of inhaled mist in the respiratory system is highlighted as a decisive factor in the interactions of inhaled EC-aerosols with the organism.

The size and behavior of the human upper airway during inhalation of aerosols

INTRODUCTION

The mouth, the pharynx and the larynx are potential sites of aerosol deposition in the upper airway during inhalation of aerosolized drugs. The right angle bend of the lumen at the back of the mouth, the position of the tongue, the variable size and shape of the lumen in the pharynx and the larynx, and the breathing pattern could increase aerosol deposition in the upper airway and decrease lung deposition. Areas covered: In this review, the anatomy of the upper airway from the oral cavity to the glottis and the impact of mandibular protrusion and incisal opening on the size of the upper airway are highlighted. In addition, the impact of inhalation maneuvers, inhaler mouthpiece geometries and a stepped mouthpiece on the size of the upper airway are discussed. Expert opinion: The structure of the upper airway lumen does not have a fixed cross sectional area and is susceptible to both constriction and distension during inhalation. The size of the upper airway can be enlarged through mandibular protrusion and/or incisal opening which might decrease aerosol deposition in the upper airway and increase lung deposition.

Predicted Deposition of E-Cigarette Aerosol in the Human Lungs

BACKGROUND

Health effects of inhaling aerosol produced by electronic cigarettes (ECs) are still uncertain. This work analyzes ECs as specific inhalation devices, which can be characterized by aerodynamic resistance, size distribution of released droplets, and predicted regional and total lung deposition as a function of inhalation maneuver.

METHODS

The internal resistance of two types of EC and a conventional cigarette was evaluated by measuring ΔP-Q curves. Particle size distribution in EC-emitted mist was determined by laser diffraction. The measured data were used to calculate lung deposition based on two approaches: multipath particle dosimetry model (MPPD) and Finlay-Martin correlations. Computations were done for the set of ventilation parameters of an EC user, and also for a by-stander.

RESULTS

Tested ECs had higher aerodynamic resistance (1.6-1.9 mbar(0.5) min/L) than tobacco cigarette (0.56 mbar(0.5) min/L), and these values are much above the high-resistant DPIs. The average mass median diameter of droplets emitted from ECs was 410 nm, with the average GSD = 1.6. Predicted total lung deposition of the mainstream aerosol was 15%-45% depending on the breathing scheme. An expected increase of particle size in the exhaled aerosol led to predictions of 15%-30% deposition efficiency during passive vaping.

CONCLUSIONS

ECs are characterized by high inhalatory resistance, so they require stronger physical effort to transfer cloud of droplets to the lungs, as compared, for example, to DPIs. A significant amount of aerosol is then exhaled, forming an unintentional source of particles to which by-standers are exposed. From this perspective, ECs are not optimal personal aerosol delivery devices.

The clinical relevance of dry powder inhaler performance for drug delivery

BACKGROUND

Although understanding of the scientific basis of aerosol therapy with dry powder inhalers (DPIs) has increased, some misconceptions still persist. These include the beliefs that high resistance inhalers are unsuitable for some patients, that extra fine (<1.0 μm) particles improve peripheral lung deposition and that inhalers with flow rate-independent fine particle fractions (FPFs) produce a more consistent delivered dose to the lungs.

OBJECTIVES

This article aims to clarify the complex inter-relationships between inhaler design and resistance, inspiratory flow rate (IFR), FPF, lung deposition and clinical outcomes, as a better understanding may result in a better choice of DPI for individual patients.

METHODS

The various factors that determine the delivery of drug particles into the lungs are reviewed. These include aerodynamic particle size distribution, the inspiratory manoeuvre, airway geometry and the three basic principles that determine the site and extent of deposition: inertial impaction, sedimentation and diffusion. DPIs are classed as either dependent or independent of inspiratory flow rate and vary in their internal resistance to inspiration. The effects of these characteristics on drug deposition in the airways are described using data from studies directly comparing currently available inhaler devices.

RESULTS

Clinical experience shows that most patients can use a high resistance DPI effectively, even during exacerbations. Particles in the aerodynamic size range from 1.5-5 μm are shown to be optimal, as particles <1.0 μm are very likely to be exhaled again while those >5 μm may impact on the oropharynx. For DPIs with a constant FPF at all flow rates, less of the delivered dose reaches the central and peripheral lung when the flow rate increases, risking under-dosing of the required medication. In contrast, flow rate-dependent inhalers increase their FPF output at higher flow rates, which compensates for the greater impaction on the upper airways as flow rate increases.

CONCLUSIONS

The technical characteristics of different inhalers and the delivery and deposition of the fine particle dose to the lungs may be important additional considerations to help the physician to select the most appropriate device for the individual patient to optimise their treatment.

Optimizing the primary particle size distributions of pressurized metered dose inhalers by using inkjet spray drying for targeting desired regions of the lungs

Conventional suspension pressurized metered dose inhalers (pMDIs) suffer not only from delivering small amounts of a drug to the lungs, but also the inhaled dose scatters all over the lung regions. This results in much less of the desired dose being delivered to regions of the lungs. This study aimed to improve the aerosol performance of suspension pMDIs by producing primary particles with narrow size distributions. Inkjet spray drying was used to produce respirable particles of salbutamol sulfate. The Next Generation Impactor (NGI) was used to determine the aerosol particle size distribution and fine particle fraction (FPF). Furthermore, oropharyngeal models were used with the NGI to compare the aerosol performances of a pMDI with monodisperse primary particles and a conventional pMDI. Monodisperse primary particles in pMDIs showed significantly narrower aerosol particle size distributions than pMDIs containing polydisperse primary particles. Monodisperse pMDIs showed aerosol deposition on a single stage of the NGI as high as 41.75 ± 5.76%, while this was 29.37 ± 6.79% for a polydisperse pMDI. Narrow size distribution was crucial to achieve a high FPF (49.31 ± 8.16%) for primary particles greater than 2 µm. Only small polydisperse primary particles with sizes such as 0.65 ± 0.28 µm achieved a high FPF with (68.94 ± 6.22%) or without (53.95 ± 4.59%) a spacer. Oropharyngeal models also indicated a narrower aerosol particle size distribution for a pMDI containing monodisperse primary particles compared to a conventional pMDI. It is concluded that, pMDIs formulated with monodisperse primary particles show higher FPFs that may target desired regions of the lungs more effectively than polydisperse pMDIs.

Deposition, imaging, and clearance: what remains to be done?

Deposition and clearance studies are used during product development and in fundamental research. These studies mostly involve radionuclide imaging, but pharmacokinetic methods are also used to assess the amount of drug absorbed through the lungs, which is closely related to lung deposition. Radionuclide imaging may be two-dimensional (gamma scintigraphy or planar imaging), or three-dimensional (single photon emission computed tomography and positron emission tomography). In October 2009, a group of scientists met at the "Thousand Years of Pharmaceutical Aerosols" conference in Reykjavik, Iceland, to discuss future research in key areas of pulmonary drug delivery. This article reports the session on "Deposition, imaging and clearance." The objective was partly to review our current understanding, but more importantly to assess "what remains to be done?" A need to standardize methodology and provide a regulatory framework by which data from radionuclide imaging methods could be compared between centers and used in the drug approval process was recognized. There is also a requirement for novel radiolabeling methods that are more representative of production processes for dry powder inhalers and pressurized metered dose inhalers. A need was identified for studies to aid our understanding of the relationship between clinical effects and regional deposition patterns of inhaled drugs. A robust methodology to assess clearance from small conducting airways should be developed, as a potential biomarker for therapies in cystic fibrosis and other diseases. The mechanisms by which inhaled nanoparticles are removed from the lungs, and the factors on which their removal depends, require further investigation. Last, and by no means least, we need a better understanding of patient-related factors, including how to reduce the variability in pulmonary drug delivery, in order to improve the precision of deposition and clearance measurements.

Modeling airflow and particle transport/deposition in pulmonary airways

A review of research papers is presented, pertinent to computer modeling of airflow as well as nano- and micron-size particle deposition in pulmonary airway replicas. The key modeling steps are outlined, including construction of suitable airway geometries, mathematical description of the air-particle transport phenomena and computer simulation of micron and nanoparticle depositions. Specifically, diffusion-dominated nanomaterial deposits on airway surfaces much more uniformly than micron particles of the same material. This may imply different toxicity effects. Due to impaction and secondary flows, micron particles tend to accumulate around the carinal ridges and to form "hot spots", i.e., locally high concentrations which may lead to tumor developments. Inhaled particles in the size range of 20nm< or =dp< or =3microm may readily reach the deeper lung region. Concerning inhaled therapeutic particles, optimal parameters for mechanical drug-aerosol targeting of predetermined lung areas can be computed, given representative pulmonary airways.

Effects of Oral Airway Geometry Characteristics on the Diffusional Deposition of Inhaled Nanoparticles

The deposition of ultrafine aerosols in the respiratory tract presents a significant health risk due to the increased cellular-level response that these particles may invoke. However, the effects of geometric simplifications on local and regional nanoparticle depositions remain unknown for the oral airway and throughout the respiratory tract. The objective of this study is to assess the effects of geometric simplifications on diffusional transport and deposition characteristics of inhaled ultrafine aerosols in models of the extrathoracic oral airway. A realistic model of the oral airway with the nasopharynx (NP) included has been constructed based on computed tomography scans of a healthy adult in conjunction with measurements reported in the literature. Three other geometries with descending degrees of physical realism were then constructed with successive geometric simplifications of the realistic model. A validated low Reynolds number k-ω turbulence model was employed to simulate laminar, transitional, and fully turbulent flow regimes for the transport of 1–200 nm particles. Results of this study indicate that the geometric simplifications considered did not significantly affect the total deposition efficiency or maximum local deposition enhancement of nanoparticles. However, particle transport dynamics and the underlying flow characteristics such as separation, turbulence intensity, and secondary motions did show an observable sensitivity to the geometric complexity. The orientation of the upper trachea was shown to be a major factor determining local deposition downstream of the glottis and should be retained in future models of the respiratory tract. In contrast, retaining the NP produced negligible variations in airway dynamics and could be excluded for predominantly oral breathing conditions. Results of this study corroborate the use of existing diffusion correlations based on a circular oral airway model. In comparison to previous studies, an improved correlation for the deposition of nanoparticles was developed based on a wider range of particle sizes and flow rates, which captures the dependence of the Sherwood number on both Reynolds and Schmidt numbers.

Studies of the Human Oropharyngeal Airspaces Using Magnetic Resonance Imaging IV—The Oropharyngeal Retention Effect for Four Inhalation Delivery Systems

Magnetic resonance imaging (MRI) of the oropharyngeal region from 20 adult volunteers using four model inhalation devices (varying mouthpiece diameters, airflow resistances) and tidal breathing was carried out. Statistical analysis (convex hull method) selected 12 scans from 80 data sets representing the extremes of all dimensions in the population. Twelve physical mouth-throat models were made by stereolithography using the exact scan data. The aim was to produce models with varying dimensions to span the adult population, and to investigate if oropharyngeal dimensions affected throat retention for different delivery systems. In an in vitro analysis, the models were used to determine the retention effect of the oropharyngeal airspaces when drug aerosols were administered from four inhalation delivery systems: a pressurised metered dose inhaler (pMDI), two different dry powder inhalers (DPIs A and B), and a nebulizer. The aims of this work were to determine the key parameters governing mouth-throat retention and whether retention was dependent on the delivery system used. Characterizing the throat models by measuring 51 different dimensional variables enabled determination of the most influential variables for dose retention for each inhalation delivery system. Throat model retention was found to be dependent on the delivery system (pMDI approximately DPI(A) > DPI(B) > Neb.). The most influential variable was the total throat model volume. Throat models representing high, median, and low oropharyngeal filtration in healthy adults have been identified.

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.

Transport and Deposition of Micro-Aerosols in Realistic and Simplified Models of the Oral Airway

A number of in vivo, in vitro and numerical studies have considered flow field characteristics and micro-particle deposition in the oral airway extending from the mouth through the larynx. These studies have highlighted the effects of flow rates, turbulence and particle characteristics on deposition values in realistic and simplified geometries. However, the effect of geometry simplifications on regional and local deposition patterns remains largely un-quantified for the oral airway and throughout the respiratory tract. The objective of this study is to assess the effects of geometry simplifications on regionally averaged and local micro-aerosol deposition characteristics in models of the extrathoracic oral airway. To achieve this objective, a realistic model of the oral airway has been constructed based on CT scans of a healthy adult in conjunction with measurements reported in the literature. Three other geometries with descending degrees of physical realism were constructed based on successive geometric simplifications of the realistic model. A validated low Reynolds number (LRN) k-omega turbulence model was employed to simulate laminar, transitional and fully turbulent flow regimes for 1-31 microm particles. Geometric simplifications were found to have a significant effect on aerosol dynamics, hot spot formations and cellular-level deposition values in the extrathoracic airway models considered. For all models, regional deposition efficiency results were found to be approximately within one standard deviation of available experimental data when plotted as a function of Stokes number. The realistic geometry provided the best predictions of regional deposition in comparison to experimental data as a function of particle diameter. Considering localized deposition, maximum deposition enhancement factors, which represent the ratio of local to total deposition, were one to two orders of magnitude higher for the realistic model. Geometric factors that significantly contributed to enhanced particle localization in the realistic model include a triangular-shaped glottis and a dorsal-sloped trachea. Therefore, highly realistic models of the oral airway geometry may be necessary to evaluate localized deposition patterns and hot spot formations, which are critical for accurately predicting cellular-level dose.

Effect of Oropharyngeal Length in Drug Lung Delivery via Suspension Pressurized Metered Dose Inhalers

PURPOSE

To determine the effect of the oropharyngeal length in adults on the lung dose of a suspension pressurized metered dose inhaler, and whether employing small volume spacers can alter this role.

METHODS

Depositions of Ventolin Evohaler (100) microg in the oropharyngeal models of two healthy adult subjects with 17.1 cm (short cast) and 19.9 cm (long cast) centerline lengths via three small volume spacers [two spacers with 3 cm effective length but one with 6.5 cm2 (L3) and the other with 24.6 cm2 (L3W) cross sections, and the Optimiser] were studied.

RESULTS

Without using spacers, lung dose of the long cast (19.52 +/- 2.32 microg, mean +/- standard deviation) was significantly larger than that for the short cast (8.08 +/- 1.01 microg, p < 0.006). However, using the L3 spacer with the short cast made the lung dose (18.59 +/- 3.33 microg) similar to that for the long cast alone. Lung doses of the short cast (20.43 +/- 1.42 microg) and the long cast (30.81 +/- 1.84 microg) with the L3W spacer were similar to those with the L3 spacer. However, using the Optimiser spacer increased the lung dose for the short cast (22.27 +/- 6.03 microg) and significantly for the long cast (35.61 +/- 2.19 microg, p < 0.006) compared to those for the L3 spacer. Using spacers increased drug deposition in the oropharynx part of the short cast, and this reduced the lung dose compared to that for the long cast.

CONCLUSION

The oropharyngeal length in adults may affect the lung dose via the pMDIs, which may not be eliminated by using small volume spacers.

Air classifier technology (ACT) in dry powder inhalation

In this study, the in vitro fine particle deposition from a multi dose dry powder inhaler (Novolizer) with air classifier technology has been investigated. It is shown that different target values for the fine particle fraction (fpf<5 microm) of the same drug can be achieved in a well-controlled way. This is particularly relevant to the application of generic formulations in the inhaler. The well-controlled and predictable fpf is achieved through dispersion of different types of formulations in exactly the same classifier concept. On the other hand, it is shown that air classifier-based inhalers are less sensitive to the carrier surface and bulk properties than competitive inhalers like the Diskus. For 10 randomly selected lactose carriers for inhalation from four different suppliers, the budesonide fpf (at 4 kPa) from the Novolizer varied between 30 and 46% (of the measured dose; R.S.D.=14.2%), whereas the extremes in fpf from the Diskus dpi were 7 and 44% (R.S.D.=56.2%) for the same formulations. The fpf from a classifier-based inhaler appears to be less dependent of the amount of lactose (carrier) fines (<15 microm) in the mixture too. Classifier-based inhalers perform best with coarse carriers that have relatively wide size distributions (e.g. 50-350 microm) and surface discontinuities inside which drug particles can find shelter from press-on forces during mixing. Coarse carrier fractions have good flow properties, which increases the dose measuring accuracy and reproducibility. The fpf from the Novolizer increases with increasing pressure drop across the device. On theoretical grounds, it can be argued that this yields a more reproducible therapy, because it compensates for a shift in deposition to larger airways when the flow rate is increased. Support for this reasoning based on lung deposition modelling studies has been found in a scintigraphic study with the Novolizer. Finally, it is shown that this inhaler produces a finer aerosol than competitor devices, within the fpf<5 microm, subfractions of particles (e.g. <1, 1-2, 2-3, 3-4 and 4-5 microm) are higher.

Effect of device inhalational resistance on the three-dimensional configuration of the upper airway

Entrainment and de-aggregation of aerosol particles from dry powder inhalers (DPIs) is achieved by a forceful inhalation from the device by the patient and by the airflow resistance built into the device. The aerodynamic shear stress imposed by the upper airway also plays an important role in the de-aggregation process. In this study the effect of device airflow resistance on the upper airway shape is determined. Seven healthy subjects inhaled via a test inhaler of different resistances (0.2 x 10(5) to 2.2 x 10(5) N(0.5).s.m(-4)) while the upper airway was imaged using magnetic resonance imaging. Decreasing the test inhaler resistance led to an increase in the cross-sectional areas of the upper airway at the oral cavity, oropharynx and larynx, while the cross-sectional areas of the upper trachea remained rather constant. The mean volume of the upper airway also increased from 72 (22) cm3 (mean (SD)) to 101 (25) cm3 by decreasing device airflow resistance from 2.2 x 10(5) to 0.2 x 10(5) N(0.5).s.m(-4). In conclusion, this study shows a significant variation in the shape of the upper airway during inhalation via devices with different resistances. This may aid understanding of drug deposition in the lungs from DPIs.

Suitability of the Upper Airway Models Obtained from MRI Studies in Simulating Drug Lung Deposition from Inhalers

PURPOSE

In this study, the suitability of the upper airway models, obtained by applying a magnetic resonance imaging method, in simulating in vivo aerosol deposition data is determined.

METHODS

Depositions of salbutamol sulfate from two nebulizers in two models, one with constriction at the oropharynx (the constricted cast) and another model without that constriction (the wide cast), were determined.

RESULTS

For the Sidestream and Ventstream nebulizer, 76 +/- 3% (mean +/- standard deviation) and 81 +/- 2% of the emitted dose deposited in the constricted cast, whereas 51 +/- 2% and 49 +/- 3% of the emitted dose deposited in the wide cast, respectively. These values were in good agreement with in vivo data. Mostly, increasing nebulizer charge volume (by normal saline) from 2.5 ml to 5 ml increased significantly the lung dose. However, the lung doses from the Sidestream and Ventstream nebulizer with 2.5 ml charge volume via the wide cast were (1.37 +/- 0.06 and 1.38 +/- 0.05 mg) significantly larger than those for the constricted cast with 5 ml charge volume (0.87 +/- 0.15 and 0.86 +/- 0.21 mg, respectively) (p = 0.005).

CONCLUSIONS

The upper airway models closely simulated the in vivo deposition data. Optimizing the upper airway posture during inhalation via the nebulizers would be more efficient in increasing drug lung delivery than diluting their contents.