Advances in aerosols: adult respiratory disease

An overview of atmospheric aerosol and their effects on human health

Epidemiologic investigations have previously been published in more than 200 papers, and several studies have examined the impacts of particle air pollution on health. The main conclusions now being made about the epidemiological evidence of particle pollution-induced health impacts are discussed in this article. Although there is no universal agreement, most reviewers conclude that particulate air pollution, particularly excellent combustion-cause contamination prevalent in many municipal and manufacturing environments, is a significant risk for cardiopulmonary sickness and mortality. Most epidemiological research has concentrated on the impacts of acute exposure, although the total public health implications of chronic acquaintance's outcome may be more extraordinarily significant. According to some reviewers, prolonged, repeated exposure raises the risk of cardiorespiratory death and chronic respiratory illness. A more general (but still universal) agreement is that short-term particle pollution exposure has been shown to aggravate pre-existing pulmonary and cardiovascular diseases and increase the number of community members who become sick, require medical treatment, or die. Several in-depth studies conducted in the global and Indian regions are addressed.

Revisiting Airflow and Aerosol Transport Phenomena in the Deep Lungs with Microfluidics

The dynamics of respiratory airflows and the associated transport mechanisms of inhaled aerosols characteristic of the deep regions of the lungs are of broad interest in assessing both respiratory health risks and inhalation therapy outcomes. In the present review, we present a comprehensive discussion of our current understanding of airflow and aerosol transport phenomena that take place within the unique and complex anatomical environment of the deep lungs, characterized by submillimeter 3D alveolated airspaces and nominally slow resident airflows, known as low-Reynolds-number flows. We exemplify the advances brought forward by experimental efforts, in conjunction with numerical simulations, to revisit past mechanistic theories of respiratory airflow and particle transport in the distal acinar regions. Most significantly, we highlight how microfluidic-based platforms spanning the past decade have accelerated opportunities to deliver anatomically inspired in vitro solutions that capture with sufficient realism and accuracy the leading mechanisms governing both respiratory airflow and aerosol transport at true scale. Despite ongoing challenges and limitations with microfabrication techniques, the efforts witnessed in recent years have provided previously unattainable in vitro quantifications on the local transport properties in the deep pulmonary acinar airways. These may ultimately provide new opportunities to explore improved strategies of inhaled drug delivery to the deep acinar regions by investigating further the mechanistic interactions between airborne particulate carriers and respiratory airflows at the pulmonary microscales.

Devices for Improved Delivery of Nebulized Pharmaceutical Aerosols to the Lungs

Nebulizers have a number of advantages for the delivery of inhaled pharmaceutical aerosols, including the use of aqueous formulations and the ability to deliver process-sensitive proteins, peptides, and biological medications. A frequent disadvantage of nebulized aerosols is poor lung delivery efficiency, which wastes valuable medications, increases delivery times, and may increase side effects of the medication. A focus of previous development efforts and previous nebulizer reviews, has been an improvement of the underlying nebulization technology controlling the breakup of a liquid into droplets. However, for a given nebulization technology, a wide range of secondary devices and strategies can be implemented to significantly improve lung delivery efficiency of the aerosol. This review focuses on secondary devices and technologies that can be implemented to improve the lung delivery efficiency of nebulized aerosols and potentially target the region of drug delivery within the lungs. These secondary devices may (1) modify the aerosol size distribution, (2) synchronize aerosol delivery with inhalation, (3) reduce system depositional losses at connection points, (4) improve the patient interface, or (5) guide patient inhalation. The development of these devices and technologies is also discussed, which often includes the use of computational fluid dynamic simulations, three-dimensional printing and rapid prototype device and airway model construction, realistic in vitro experiments, and in vivo analysis. Of the devices reviewed, the implementation of streamlined components may be the most direct and lowest cost approach to enhance aerosol delivery efficiency within nonambulatory nebulizer systems. For applications involving high-dose medications or precise dose administration, the inclusion of active devices to control aerosol size, guide inhalation, and synchronize delivery with inhalation hold considerable promise.

Investigation of Fugitive Aerosols Released into the Environment during High-Flow Therapy

BACKGROUND

Nebulised medical aerosols are designed to deliver drugs to the lungs to aid in the treatment of respiratory diseases. However, an unintended consequence is the potential for fugitive emissions during patient treatment, which may pose a risk factor in both clinical and homecare settings.

METHODS

The current study examined the potential for fugitive emissions, using albuterol sulphate as a tracer aerosol during high-flow therapy. A nasal cannula was connected to a head model or alternatively, a interface was connected to a tracheostomy tube in combination with a simulated adult and paediatric breathing profile. Two aerodynamic particle sizers (APS) recorded time-series aerosol concentrations and size distributions at two different distances relative to the simulated patient.

RESULTS

The results showed that the quantity and characteristics of the fugitive emissions were influenced by the interface type, patient type and supplemental gas-flow rate. There was a trend in the adult scenarios; as the flow rate increased, the fugitive emissions and the mass median aerodynamic diameter (MMAD) of the aerosol both decreased. The fugitive emissions were comparable when using the adult breathing profiles for the nasal cannula and tracheostomy interfaces; however, there was a noticeable distinction between the two interfaces when compared for the paediatric breathing profiles. The highest recorded aerosol concentration was 0.370 ± 0.046 mg m-3 from the tracheostomy interface during simulated paediatric breathing with a gas-flow rate of 20 L/min. The averaged MMAD across all combinations ranged from 1.248 to 1.793 µm by the APS at a distance of 0.8 m away from the patient interface.

CONCLUSIONS

Overall, the results highlight the potential for secondary inhalation of fugitive emissions released during simulated aerosol treatment with concurrent high-flow therapy. The findings will help in developing policy and best practice for risk mitigation from fugitive emissions.

Investigation of the Quantity of Exhaled Aerosols Released into the Environment during Nebulisation

BACKGROUND

Secondary inhalation of medical aerosols is a significant occupational hazard in both clinical and homecare settings. Exposure to fugitive emissions generated during aerosol therapy increases the risk of the unnecessary inhalation of medication, as well as toxic side effects.

METHODS

This study examines fugitively-emitted aerosol emissions when nebulising albuterol sulphate, as a tracer aerosol, using two commercially available nebulisers in combination with an open or valved facemask or using a mouthpiece with and without a filter on the exhalation port. Each combination was connected to a breathing simulator during simulated adult breathing. The inhaled dose and residual mass were quantified using UV spectrophotometry. Time-varying fugitively-emitted aerosol concentrations and size distributions during nebulisation were recorded using aerodynamic particle sizers at two distances relative to the simulated patient. Different aerosol concentrations and size distributions were observed depending on the interface.

RESULTS

Within each nebuliser, the facemask combination had the highest time-averaged fugitively-emitted aerosol concentration, and values up to 0.072 ± 0.001 mg m-3 were recorded. The placement of a filter on the exhalation port of the mouthpiece yielded the lowest recorded concentrations. The mass median aerodynamic diameter of the fugitively-emitted aerosol was recorded as 0.890 ± 0.044 µm, lower the initially generated medical aerosol in the range of 2⁻5 µm.

CONCLUSIONS

The results highlight the potential secondary inhalation of exhaled aerosols from commercially available nebuliser facemask/mouthpiece combinations. The results will aid in developing approaches to inform policy and best practices for risk mitigation from fugitive emissions.

Development and comparison of new high-efficiency dry powder inhalers for carrier-free formulations

High-efficiency dry powder inhalers (DPIs) were developed and tested for use with carrier-free formulations across a range of different inhalation flow rates. Performance of a previously reported DPI was compared with two new designs in terms of emitted dose (ED) and aerosolization characteristics using in vitro experiments. The two new designs oriented the capsule chamber (CC) at different angles to the main flow passage, which contained a three-dimensional (3D) rod array for aerosol deaggregation. Computational fluid dynamics simulations of a previously developed deaggregation parameter, the nondimensional specific dissipation (NDSD), were used to explain device performance. Orienting the CC at 90° to the mouthpiece, the CC90 -3D inhaler provided the best performance with an ED = 73.4%, fine particle fractions (FPFs) less than 5 and 1 μm of 95.1% and 31.4%, respectively, and a mass median aerodynamic diameter (MMAD) = 1.5 μm. For the carrier-free formulation, deaggregation was primarily influenced by capsule aperture position and the NDSD parameter. The new CC-3D inhalers reduced the percent difference in FPF and MMAD between low and high flows by 1-2 orders of magnitude compared with current commercial devices. In conclusion, the new CC-3D inhalers produced extremely high-quality aerosols with little sensitivity to flow rate and are expected to deliver approximately 95% of the ED to the lungs.

Clinical experimentation with aerosol antibiotics: current and future methods of administration

Currently almost all antibiotics are administered by the intravenous route. Since several systems and situations require more efficient methods of administration, investigation and experimentation in drug design has produced local treatment modalities. Administration of antibiotics in aerosol form is one of the treatment methods of increasing interest. As the field of drug nanotechnology grows, new molecules have been produced and combined with aerosol production systems. In the current review, we discuss the efficiency of aerosol antibiotic studies along with aerosol production systems. The different parts of the aerosol antibiotic methodology are presented. Additionally, information regarding the drug molecules used is presented and future applications of this method are discussed.

Targeting aerosol deposition to and within the lung airways using excipient enhanced growth

BACKGROUND

Previous studies have characterized the size increase of combination submicrometer particles composed of a drug and hygroscopic excipient when exposed to typical airway thermodynamic conditions. The objective of this study was to determine the deposition and size increase characteristics of excipient enhanced growth (EEG) aerosols throughout the tracheobronchial (TB) airways and to evaluate the potential for targeted delivery.

METHODS

Submicrometer particles composed of a poorly water-soluble drug (insulin) and hygroscopic excipient (sodium chloride) were considered at drug:excipient mass ratios of 50:50 and 25:75. A previously validated computational fluid dynamics model was used to predict aerosol size increase and deposition in characteristic geometries of the mouth-throat (MT), upper TB airways through the third bifurcation (B3), and remaining TB airways through B15. Additional validation experiments were also performed for albuterol sulfate:mannitol particles. Both growth of combination particles and deposition are reported throughout the conducting airways for characteristic slow and deep (SD) and quick and deep (QD) inhalations.

RESULTS

For all EEG cases considered, MT deposition was less than 1% of the drug dose, which is at least one order of magnitude lower than with state-of-the-art and conventional inhalers. Final aerosol sizes exiting the TB region and entering the alveolar airways were all greater than 3 μm. For SD inhalation, deposition fractions of 20% were achieved in the lower TB region of B8-B15, which is a factor of 20-30×higher than conventional delivery devices. With QD inhalation, maximum alveolar delivery of 90% was observed.

CONCLUSIONS

Increasing the dose delivered to the lower TB region by a factor of 20-30×or achieving 90% delivery to the alveolar airways was considered effective aerosol targeting compared with conventional devices. The trend of higher flow rates resulting in better alveolar delivery of aerosols is unique to EEG and may be used to design highly efficient dry powder inhalers.

Performance of combination drug and hygroscopic excipient submicrometer particles from a softmist inhaler in a characteristic model of the airways

Excipient enhanced growth (EEG) of inhaled submicrometer pharmaceutical aerosols is a recently proposed method intended to significantly reduce extrathoracic deposition and improve lung delivery. The objective of this study was to evaluate the size increase of combination drug and hygroscopic excipient particles in a characteristic model of the airways during inhalation using both in vitro experiments and computational fluid dynamic (CFD) simulations. The airway model included a characteristic mouth-throat (MT) and upper tracheobronchial (TB) region through the third bifurcation and was enclosed in a chamber geometry used to simulate the thermodynamic conditions of the lungs. Both in vitro results and CFD simulations were in close agreement and indicated that EEG delivery of combination submicrometer particles could nearly eliminate MT deposition for inhaled pharmaceutical aerosols. Compared with current inhalers, the proposed delivery approach represents a 1-2 order of magnitude reduction in MT deposition. Transient inhalation was found to influence the final size of the aerosol based on changes in residence times and relative humidity values. Aerosol sizes following EEG when exiting the chamber (2.75-4.61 μm) for all cases of initial submicrometer combination particles were equivalent to or larger than many conventional pharmaceutical aerosols that frequently have MMADs in the range of 2-3 μm.

Aerosol delivery through tracheostomy tubes: an in vitro study

BACKGROUND

Our study investigated the influence of the cannula's inner diameter (ID) and of its removal on the expected respiratory dose of amikacin, using three different jet nebulizer configurations (Sidestream(®)): vented (N1), unvented with a piece of corrugated tubing attached to the expiratory limb of the T attachment (N2), and unvented alone (N3).

METHODS

The jet nebulizer was filled with amikacin (500 mg/4 mL) and was attached to the tracheostomy tube. A lung model simulating spontaneous breathing was connected to the tracheostomy tube. A filter was connected between the nebulizer and the tracheostomy tube to measure the inhaled dose, and between the tracheostomy tube and the lung model to measure the respiratory dose. Different cannula IDs were tested (6.5, 8, 8.5, and 10 mm), and aerosol lost in the cannulas was determined.

RESULTS AND CONCLUSIONS

Respiratory dose varied between 96±1 mg and 44±3 mg, with higher values observed with N2. The aerosol lost in the cannula was significant and represented up to 63% of the inhaled dose. There was a negative correlation between the cannula's ID and the aerosol lost in the cannula. After removal of the internal cannula, an increase in the respiratory dose of up to 31.3% was observed. We recommend removing the inner tracheostomy cannula to nebulize a larger amount of drug through a tracheostomy tube. Among the three jet nebulizer configurations studied, we recommend the unvented one with a piece of corrugated tubing attached to the expiratory limb of the T attachment.

[Inhalation devices: characteristics, modeling, regulation and use in routine practice. GAT Aerosolstorming, Paris 2011]

Aerosoltherapy is a first-line treatment for chronic obstructive respiratory diseases such as asthma and COPD. Treatment modalities and devices are varied and the choice of the device must be adapted to and optimized for every patient. Spacers can be used for some categories of patients for whom the use of other devices turns out to be complicated. The improvement of these treatments requires the optimization of the lung deposition of inhaled particles; lung modeling plays an essential role in the understanding of the mechanisms of flow in the airways. Regulations must frame prescription of inhaled treatments to optimize its quality and, thus, the care for these chronic diseases. Many generally-accepted ideas concerning these treatments turn out to be false. Inhaled treatments are constantly evolving, both pharmacologically and technologically.

Aerosol drug delivery: developments in device design and clinical use

Aerosolised drugs are prescribed for use in a range of inhaler devices and systems. Delivering drugs by inhalation requires a formulation that can be successfully aerosolised and a delivery system that produces a useful aerosol of the drug; the particles or droplets need to be of sufficient size and mass to be carried to the distal lung or deposited on proximal airways to give rise to a therapeutic effect. Patients and caregivers must use and maintain these aerosol drug delivery devices correctly. In recent years, several technical innovations have led to aerosol drug delivery devices with efficient drug delivery and with novel features that take into account factors such as dose tracking, portability, materials of manufacture, breath actuation, the interface with the patient, combination therapies, and systemic delivery. These changes have improved performance in all four categories of devices: metered dose inhalers, spacers and holding chambers, dry powder inhalers, and nebulisers. Additionally, several therapies usually given by injection are now prescribed as aerosols for use in a range of drug delivery devices. In this Review, we discuss recent developments in the design and clinical use of aerosol devices over the past 10-15 years with an emphasis on the treatment of respiratory disorders.

Characterization of respiratory drug delivery with enhanced condensational growth using an individual path model of the entire tracheobronchial airways

The objective of this study was to evaluate the delivery of inhaled pharmaceutical aerosols using an enhanced condensational growth (ECG) approach in an airway model extending from the oral cavity to the end of the tracheobronchial (TB) region. The geometry consisted of an elliptical mouth-throat (MT) model, the upper TB airways extending to bifurcation B3, and a subsequent individual path model entering the right lower lobe of the lung. Submicrometer monodisperse aerosols with diameters of 560 and 900 nm were delivered to the mouth inlet under control (25 °C with subsaturated air) or ECG (39 or 42 °C with saturated air) conditions. Flow fields and droplet characteristics were simulated using a computational fluid dynamics model that was previously demonstrated to accurately predict aerosol size growth and deposition. Results indicated that both the control and ECG delivery cases produced very little deposition in the MT and upper TB model (approximately 1%). Under ECG delivery conditions, large size increases of the aerosol droplets were observed resulting in mass median aerodynamic diameters of 2.4-3.3 μm exiting B5. This increase in aerosol size produced an order of magnitude increase in aerosol deposition within the TB airways compared with the controls, with TB deposition efficiencies of approximately 32-46% for ECG conditions. Estimates of downstream pulmonary deposition indicted near full lung retention of the aerosol during ECG delivery. Furthermore, targeting the region of TB deposition by controlling the inlet temperature conditions and initial aerosol size also appeared possible.

CFD simulations of enhanced condensational growth (ECG) applied to respiratory drug delivery with comparisons to in vitro data

Enhanced condensational growth (ECG) is a newly proposed concept for respiratory drug delivery in which a submicrometer aerosol is inhaled in combination with saturated or supersaturated water vapor. The initially small aerosol size provides for very low extrathoracic deposition, whereas condensation onto droplets in vivo results in size increase and improved lung retention. The objective of this study was to develop and evaluate a CFD model of ECG in a simple tubular geometry with direct comparisons to in vitro results. The length (29 cm) and diameter (2 cm) of the tubular geometry were representative of respiratory airways of an adult from the mouth to the first tracheobronchial bifurcation. At the model inlet, separate streams of humidified air (25, 30, and 39 °C) and submicrometer aerosol droplets with mass median aerodynamic diameters (MMADs) of 150, 560, and 900 nm were combined. The effects of condensation and droplet growth on water vapor concentrations and temperatures in the continuous phase (i.e., two-way coupling) were also considered. For an inlet saturated air temperature of 39 °C, the two-way coupled numerical (and in vitro) final aerosol MMADs for initial sizes of 150, 560, and 900 nm were 1.75 μm (vs. 1.23 μm), 2.58 μm (vs. 2.66 μm), and 2.65 μm (vs. 2.63 μm), respectively. By including the effects of two-way coupling in the model, agreements with the in vitro results were significantly improved compared with a one-way coupled assumption. Results indicated that both mass and thermal two-way coupling effects were important in the ECG process. Considering the initial aerosol sizes of 560 and 900 nm, the final sizes were most influenced by inlet saturated air temperature and aerosol number concentration and were not largely influenced by initial size. Considering the growth of submicrometer aerosols to above 2 μm at realistic number concentrations, ECG may be an effective respiratory drug delivery approach for minimizing mouth-throat deposition and maximizing aerosol retention in a safe and simple manner. However, future studies are needed to explore effects of in vivo boundary conditions, more realistic respiratory geometries, and transient breathing.

Domiciliary experience of the Target Inhalation Mode (TIM) breathing maneuver in patients with cystic fibrosis

BACKGROUND

The time requirements for multiple daily nebulizer treatments are important impediments to the quality of life for most patients with cystic fibrosis (CF). The I-neb Adaptive Aerosol Delivery (AAD) System can be used with a new mode of breathing during inhalation of aerosol, the Target Inhalation Mode (TIM). As a function of the TIM algorithm, the patient is guided to a slow and deep inhalation, which can result in shorter treatment times.

METHODS

This study was conducted as a 3-month patient handling study of the I-neb AAD System in 42 patients with CF aged 12-57 years. The I-neb AAD System was supplied in both the standard Tidal Breathing Mode (TBM), and in TIM. Patients were trained to use the I-neb AAD System in TIM for the delivery of all their inhaled medications, but if they were not comfortable with the TIM maneuver they could change to the TBM maneuver. The primary variables were compliance with the correct use of the I-neb AAD System, and treatment times. The secondary variables were based on study questionnaires at the end of the study and covered ease of use, patient confidence, and patient satisfaction with the I-neb AAD System.

RESULTS

There were a total of 10,240 complete treatments and of these, 8979 (88%) were in TIM. Compliance with the correct use of the I-neb AAD System was 97.6%. The mean treatment time for complete treatments in TIM was 4.20 min, compared with 6.83 min when using the I-neb AAD System in TBM. The responses to the questionnaires indicated that over 77% of the patients found the I-neb AAD System in TIM to be either: very easy, easy, or acceptable to use.

CONCLUSIONS

The results demonstrated that by using the I-neb AAD System in TIM, a 40-50% reduction of nebulizer treatment times, and a high level of compliance could be achieved. The results also showed that the patients found the I-neb AAD System easy to use.

Characterization of Nanoaerosol Size Change During Enhanced Condensational Growth

Increasing the size of nanoaerosols may be beneficial in a number of applications including filtration, particle size selection, and targeted respiratory drug delivery. A potential method to increase particle or droplet size is enhanced condensational growth (ECG), which involves combining the aerosol with saturated or supersaturated air. In this study, we characterize the ECG process in a model tubular geometry as a function of initial aerosol size (mean diameters - 150, 560 and 900 nm) and relative humidity conditions using both in vitro experiments and numerical modeling. Relative humidities (99.8 - 104%) and temperatures (25 - 39 °C) were evaluated that can safely be applied to either targeted respiratory drug delivery or personal aerosol filtration systems. For inlet saturated air temperatures above ambient conditions (30 and 39 °C), the initial nanoaerosols grew to a size range of 1000 - 3000 nm (1 - 3 μm) over a time period of 0.2 seconds. The numerical model results were generally consistent with the experimental findings and predicted final to initial diameter ratios of up to 8 after 0.2 s of humidity exposure and 14 at 1 s. Based on these observations, a respiratory drug delivery approach is suggested in which nanoaerosols in the size range of 500 nm are delivered in conjunction with a saturated or supersaturated air stream. The initial nanoaerosol size will ensure minimal deposition and loss in the mouth-throat region while condensational growth in the respiratory tract can be used to ensure maximal lung retention and to potentially target the site of deposition.

Evaluation of enhanced condensational growth (ECG) for controlled respiratory drug delivery in a mouth-throat and upper tracheobronchial model

PURPOSE

The objective of this study is to evaluate the effects of enhanced condensational growth (ECG), as a novel inhalation drug delivery method, on nano-aerosol deposition in a mouth-throat (MT) and upper tracheobronchial (TB) model using in vitro experiments and computational fluid dynamics (CFD) simulations.

METHODS

Separate streams of nebulized nano-aerosols and saturated humidified air (39 degrees C-ECG; 25 degrees C-control) were combined as they were introduced into a realistic MT-TB geometry. Aerosol deposition was determined in the MT, generations G0-G2 (trachea-lobar bronchi) and G3-G5 and compared to CFD simulations.

RESULTS

Using ECG conditions, deposition of 560 and 900 nm aerosols was low in the MT region of the MT-TB model. Aerosol drug deposition in the G0-G2 and G3-G5 regions increased due to enhanced condensational growth compared to control. CFD-predicted depositions were generally in good agreement with the experimental values.

CONCLUSIONS

The ECG platform appears to offer an effective method of delivering nano-aerosols through the extrathoracic region, with minimal deposition, to the tracheobronchial airways and beyond. Aerosol deposition is then facilitated as enhanced condensational growth increases particle size. Future studies will investigate the effects of physio-chemical drug properties and realistic inhalation profiles on ECG growth characteristics.

Comparison of the bronchodilative effects of salbutamol delivered via three mesh nebulizers in children with bronchial asthma

BACKGROUND

We compared the bronchodilative effects of salbutamol delivered via 3 different mesh nebulizers, Aeroneb-go(R)(AE), Omron-NE-U22(R)(OM) and Pari-eMotion(R)(PA).

METHODS

We enrolled 36 children with asthma who visited the Kurosaka Pediatrics and Allergy Clinic, randomly assigned to 3 groups for treatment with AE, OM or PA. The dose of salbutamol in the solution was 0.15mgx body weight (kg)(minimum 2.5mg, maximum 5mg). FEV(1), PEFR and V(50) were measured in these patients before treatment, and at 15 and 30 minutes after salbutamol inhalation using one of the 3 mesh nebulizers.

RESULTS

All groups showed a significant improvement of FEV(1), PEFR and V(50) at 30 minutes after salbutamol inhalation. The AE group did not show a significant improvement in PEFR at 15 minutes after inhalation, whereas a significant improvement in FEV(1) and V(50) was evident at the same time point. The OM group showed no significant improvement in V(50) at 15 minutes after inhalation, whereas this group clearly showed a significant improvement in PEFR and FEV(1) at the same time point.

CONCLUSIONS

Overall, all 3 mesh nebulizers were useful devices in treating bronchial asthma, although some differences in lung function improvement were evident. The limitation of this study is that subjects did not include patients with severe asthma attacks.

Evaluation of the Respimat Soft Mist Inhaler using a concurrent CFD and in vitro approach

BACKGROUND

The Respimat Soft Mist Inhaler is reported to generate an aerosol with low spray momentum and a small droplet size. However, the transport characteristics of the Respimat aerosol are not well understood. The objective of this study was to characterize the transport and deposition of an aerosol emitted from the Respimat inhaler using a combination of computational fluid dynamics (CFD) modeling and in vitro experiments.

METHODS

Deposition of the Respimat aerosol was assessed in the inhaler mouthpiece (MP), a standard induction port (IP), and a more realistic mouth-throat (MT) geometry at an inhalation flow rate of 30 L/min. Aerosols were generated using an albuterol sulfate (0.6%) solution, and the drug deposition was quantified using both in vitro experiments and a CFD model of the Respimat inhaler. Laser diffraction experiments were used to determine the initial polydisperse aerosol size distribution.

RESULTS AND CONCLUSIONS

It was found that the aerosol generated from the highly complex process of jet collision and breakup could be approximated in the model using effective spray conditions. Computational predictions of deposition fractions agreed well with in vitro results for both the IP (within 20% error) and MT (within 10% error) geometries. The experimental results indicated that the deposition fraction of drug in the MP ranged from 27 to 29% and accounted for a majority of total drug loss. Based on the CFD solution, high MP deposition was due to a recirculating flow pattern that surrounded the aerosol spray and entrained a significant number of small droplets. In contrast, deposition of the Respimat aerosol in both the IP (4.2%) and MT (7.4%) geometries was relatively low. Results of this study indicate that modifications to the current Respimat MP and control of specific patient variables may significantly reduce deposition in the device and may decrease high oropharyngeal drug loss observed in vivo.

Pulmonary Drug Delivery System for inhalation therapy in mechanically ventilated patients

The Pulmonary Drug Delivery System (PDDS) Clinical represents a newer generation of electronic nebulizers that employ a vibrating mesh or aperture plate to generate an aerosol. The PDDS Clinical is designed for aerosol therapy in patients receiving mechanical ventilation. The components of the device include a control module that is connected to the nebulizer/reservoir unit by a cable. The nebulizer contains Aerogen's OnQ aerosol generator. A pressure sensor monitors the pressure in the inspiratory limb of the ventilator circuit and provides feedback to the control module. Based on the feedback from the pressure sensor, aerosol generation occurs only during a specific part of the respiratory cycle. In bench models, the PDDS Clinical has high efficiency for aerosol delivery both on and off the ventilator, with a lower respiratory tract delivery of 50-70% of the nominal dose. Currently, the PDDS Clinical is being evaluated for the treatment of ventilator-associated pneumonia with aerosolized amikacin, an aminoglycoside antibiotic. Preliminary studies in patients with ventilator-associated pneumonia found that the administration of amikacin via PDDS reduced the need for concomitant intravenous antibiotics; however, more definitive clinical studies are needed. The PDDS Clinical delivers a high percentage of the nominal dose to the lower respiratory tract, and is well suited for inhalation therapy in mechanically ventilated patients.

Current therapies and technological advances in aqueous aerosol drug delivery

Recent advances in aerosolization technology have led to renewed interest in pulmonary delivery of a variety of drugs. Pressurized metered dose inhalers (pMDIs) and dry powder inhalers (DPIs) have experienced success in recent years; however, many limitations are presented by formulation difficulties, inefficient delivery, and complex device designs. Simplification of the formulation process as well as adaptability of new devices has led many in the pharmaceutical industry to reconsider aerosolization in an aqueous carrier. In the acute care setting, breath-enhanced air-jet nebulizers are controlling and minimizing the amount of wasted medication, while producing a high percentage of respirable droplets. Vibrating mesh nebulizers offer advantages in higher respirable fractions (RFs) and slower velocity aerosols when compared with air-jet nebulizers. Vibrating mesh nebulizers incorporating formulation and patient adaptive components provide improvements to continuous nebulization technology by generating aerosol only when it is most likely to reach the deep lung. Novel innovations in generation of liquid aerosols are now being adapted for propellant-free pulmonary drug delivery to achieve unprecedented control over dose delivered and are leading the way for the adaptation of systemic drugs for delivery via the pulmonary route. Devices designed for the metered dose delivery of insulin, morphine, sildenafil, triptans, and various peptides are all currently under investigation for pulmonary delivery to treat nonrespiratory diseases. Although these devices are currently still in clinical testing (with the exception of the Respimat), metered dose liquid inhalers (MDLIs) have already shown superior outcomes to current pulmonary and systemic delivery methods.

How best to deliver aerosol medications to mechanically ventilated patients

Pressurized metered-dose inhalers (pMDIs) and nebulizers are employed routinely for aerosol delivery to ventilator-supported patients, but the ventilator circuit and artificial airway previously were thought to be major barriers to effective delivery of aerosols to patients receiving mechanical ventilation. In the past two decades, several investigators have shown that careful attention to many factors, such as the position of the patient, the type of aerosol generator and its configuration in the ventilator circuit, aerosol particle size, artificial airway, conditions in the ventilator circuit, and ventilatory parameters, is necessary to optimize aerosol delivery during mechanical ventilation. The best techniques for aerosol delivery during noninvasive positive-pressure ventilation are not well established as yet, and the efficiency of aerosol delivery in this setting is lower than that during invasive mechanical ventilation. The most efficient methods of using the newer hydrofluoroalkane-pMDIs and vibrating mesh nebulizers in ventilator-supported patients also require further evaluation. When optimal techniques of administration are employed, the efficiency of aerosolized drug delivery in mechanically ventilated patients is comparable to that achieved in ambulatory patients.

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.

Effect of inhaled tacrolimus on cellular and humoral rejection to prevent posttransplant obliterative airway disease

This study aimed to investigate the pharmacokinetics after tacrolimus aerosol inhalation and to assess its efficacy to suppress acute and chronic airway allograft rejection. Orthotopic tracheal transplantations were performed and tacrolimus (4 mg/kg) was administered orally (PO) or via aerosol (AER). Tracheal tissue level AUCs(0-12) were similar in both treatment groups, but blood AUCs(0-12) were approximately 5.5-fold lower with AER (p < 0.001). Interestingly, only PO animals showed elevated BUN, cholesterol and triglycerides on POD 60 (p < 0.05). Histology of grafts harvested after 6 and 60 days revealed that both treatment groups were similarly effective in suppressing graft mononuclear infiltration (p < 0.001). Cellular immune activation (assessed by IFN-gamma- and IL-4-ELISPOTS), however, was far more effectively suppressed by tacrolimus PO (p < 0.001). In both treatment groups, the vigorous alloreactive IgM-antibody surge was effectively inhibited (p < 0.001). Due to the insufficient systemic cellular immunosuppression, discontinuation of tacrolimus AER resulted in a far stronger (3.5-fold) graft infiltration on POD 8 compared to PO (p < 0.001). Tacrolimus aerosol reduces systemic side effects and effectively protects the airway graft from early cellular rejection and chronic obliterative airway disease.