Jet and ultrasonic nebuliser output: use of a new method for direct measurement of aerosol output

Development of nebulized inhalation delivery for fusion-inhibitory lipopeptides to protect non-human primates against Nipah-Bangladesh infection

Nipah virus (NiV) is a lethal zoonotic paramyxovirus that can be transmitted from person to person through the respiratory route. There are currently no licensed vaccines or therapeutics. A lipopeptide-based fusion inhibitor was developed and previously evaluated for efficacy against the NiV-Malaysia strain. Intraperitoneal administration in hamsters showed superb prophylactic activity and promising efficacy, however the intratracheal delivery mode in non-human primates proved intractable and spurred the development of an aerosolized delivery route that could be clinically applicable. We developed an aerosol delivery system in an artificial respiratory 3D model and optimized the combinations of flow rate and particle size for lung deposition. We characterized the nebulizer device and assessed the safety of lipopeptide nebulization in an African green monkey model that mimics human NiV infection. Three nebulized doses of fusion-inhibitory lipopeptide were administered every 24 h, resulting in peptide deposition across multiple regions of both lungs without causing toxicity or adverse hematological and biochemical effects. In peptide-treated monkeys challenged with a lethal dose of NiV-Bangladesh, animals retained robust levels of T and B-lymphocytes in the blood, infection-induced lethality was significantly delayed, and 2 out of 5 monkeys were protected from NiV infection. The present study establishes the safety and feasibility of the nebulizer delivery method for AGM studies. Future studies will compare delivery methods using next-generation fusion-inhibitory anti-NiV lipopeptides to evaluate the potential role of this aerosol delivery approach in achieving a rapid antiviral response.

Indian Guidelines on Nebulization Therapy

Inhalational therapy, today, happens to be the mainstay of treatment in obstructive airway diseases (OADs), such as asthma, chronic obstructive pulmonary disease (COPD), and is also in the present, used in a variety of other pulmonary and even non-pulmonary disorders. Hand-held inhalation devices may often be difficult to use, particularly for children, elderly, debilitated or distressed patients. Nebulization therapy emerges as a good option in these cases besides being useful in the home care, emergency room and critical care settings. With so many advancements taking place in nebulizer technology; availability of a plethora of drug formulations for its use, and the widening scope of this therapy; medical practitioners, respiratory therapists, and other health care personnel face the challenge of choosing appropriate inhalation devices and drug formulations, besides their rational application and use in different clinical situations. Adequate maintenance of nebulizer equipment including their disinfection and storage are the other relevant issues requiring guidance. Injudicious and improper use of nebulizers and their poor maintenance can sometimes lead to serious health hazards, nosocomial infections, transmission of infection, and other adverse outcomes. Thus, it is imperative to have a proper national guideline on nebulization practices to bridge the knowledge gaps amongst various health care personnel involved in this practice. It will also serve as an educational and scientific resource for healthcare professionals, as well as promote future research by identifying neglected and ignored areas in this field. Such comprehensive guidelines on this subject have not been available in the country and the only available proper international guidelines were released in 1997 which have not been updated for a noticeably long period of over two decades, though many changes and advancements have taken place in this technology in the recent past. Much of nebulization practices in the present may not be evidence-based and even some of these, the way they are currently used, may be ineffective or even harmful. Recognizing the knowledge deficit and paucity of guidelines on the usage of nebulizers in various settings such as inpatient, out-patient, emergency room, critical care, and domiciliary use in India in a wide variety of indications to standardize nebulization practices and to address many other related issues; National College of Chest Physicians (India), commissioned a National task force consisting of eminent experts in the field of Pulmonary Medicine from different backgrounds and different parts of the country to review the available evidence from the medical literature on the scientific principles and clinical practices of nebulization therapy and to formulate evidence-based guidelines on it. The guideline is based on all possible literature that could be explored with the best available evidence and incorporating expert opinions. To support the guideline with high-quality evidence, a systematic search of the electronic databases was performed to identify the relevant studies, position papers, consensus reports, and recommendations published. Rating of the level of the quality of evidence and the strength of recommendation was done using the GRADE system. Six topics were identified, each given to one group of experts comprising of advisors, chairpersons, convenor and members, and such six groups (A-F) were formed and the consensus recommendations of each group was included as a section in the guidelines (Sections I to VI). The topics included were: A. Introduction, basic principles and technical aspects of nebulization, types of equipment, their choice, use, and maintenance B. Nebulization therapy in obstructive airway diseases C. Nebulization therapy in the intensive care unit D. Use of various drugs (other than bronchodilators and inhaled corticosteroids) by nebulized route and miscellaneous uses of nebulization therapy E. Domiciliary/Home/Maintenance nebulization therapy; public & health care workers education, and F. Nebulization therapy in COVID-19 pandemic and in patients of other contagious viral respiratory infections (included later considering the crisis created due to COVID-19 pandemic). Various issues in different sections have been discussed in the form of questions, followed by point-wise evidence statements based on the existing knowledge, and recommendations have been formulated.

Aerosol Generation and Mitigation During Methacholine Bronchoprovocation Testing: Infection Control Implications in the Era of COVID-19

BACKGROUND

Methacholine bronchoprovocation or challenge testing (MCT) is commonly performed to assess airway hyper-responsiveness in the setting of suspected asthma. Nebulization is an aerosol-generating procedure, but little is known about the risks of MCT in the context of the ongoing coronavirus disease 2019 (COVID-19) pandemic. We aimed to quantify and characterize aerosol generation during MCT by using different delivery methods and to assess the impact of adding a viral filter.

METHODS

Seven healthy subjects performed simulated MCT in a near particle-free laboratory space with 4 different nebulizers and with a dosimeter. Two devices continuously sampled the ambient air during the procedure, which detected ultrafine particles, from 0.02-1 μm, and particles of sizes 0.3, 0.5, 1.0, 2.0, 5.0, and 10 µm, respectively. Particle generation was compared among all the devices, with and without viral filter placement.

RESULTS

Ultrafine-particle generation during simulated MCT was significant across all the devices. Ultrafine-particle (0.02-1 μm) concentrations decreased 77%-91% with the addition of a viral filter and varied significantly between unfiltered (P < .001) and filtered devices (P < .001). Ultrafine-particle generation was lowest when using the dosimeter with filtered Hudson nebulizer (1,258 ± 1,644 particle/mL). Ultrafine-particle concentrations with the filtered nebulizer devices using a compressor were higher than particle concentrations detected when using the dosimeter: Monaghan (3,472 ± 1,794 particles/mL), PARI (4,403 ± 2,948), Hudson (6,320 ± 1,787) and AirLife (9,523 ± 5,098).

CONCLUSIONS

The high particle concentrations generated during MCT pose significant infection control concerns during the COVID-19 pandemic. Particle generation during MCT was significantly reduced by using breath-actuated delivery and a viral filter, which offers an effective mitigation strategy.

Viability assessment of human peripheral blood-derived stem cells after three methods of nebulization

BACKGROUND AND OBJECTIVES

Drug delivery by nebulization has become a crucial strategy for treating different respiratory and lung diseases. Emerging evidence implicates stem cell therapy as a promising tool in treating such conditions, not only by alleviating the related symptoms but by improving the prognosis. However, delivery of human peripheral blood-derived stem cells (hPBSCs) to the respiratory airways remains an innovative approach yet to be realized. This study is an analytic, translational, and in vitro research to assess the viability and morphological changes of identified cell populations in hPBSCs cocktail derived from COVID-19 patients.

METHODS AND RESULTS

Peripheral blood (PB) samples were obtained from patients enrolled in the SENTAD-COVID Study (ClinicalTrials.gov Reference: NCT04473170). hPBSCs cocktails (n=15) were provided by the Cells Processing Laboratory of Abu Dhabi Stem Cells Center, and were nebulized by three different methods of nebulization: compressor (jet), ultrasonic, and mesh. Our results reported that nucleated CD45^dim cell count was significantly lower after the three nebulization methods, but nucleated CD45^- cells show a significant decrease only after mesh nebulization. Mesh-nebulized samples had a significant reduction in viability of both CD45^dim and CD45^- cells.

CONCLUSIONS

This study provides evidence that stem cells derived from PB of COVID-19 patients can be nebulized without substantial loss of cell viability, cell count, and morphological changes using the compressor nebulization. Therefore, we recommend compressor nebulizers as the preferable procedure for hPBSCs delivery to the respiratory airways in further clinical settings.

Inhaled chemotherapy adverse effects: mechanisms and protection methods

Lung cancer is still diagnosed at a late stage due to a lack of symptoms. Although there are novel therapies, many patients are still treated with chemotherapy. In an effort to reduce adverse effects associated with chemotherapy, inhaled administration of platinum analogs has been investigated. Inhaled administration is used as a local route in order to reduce the systemic adverse effects; however, this treatment modality has its own adverse effects. In this mini review, we present drugs that were administered as nebulized droplets or dry powder aerosols for non-small-cell lung cancer. We present the adverse effects and methods to overcome them.

Inhaled Cisplatin for NSCLC: Facts and Results

Although we have new diagnostic tools for non-small cell lung cancer, diagnosis is still made in advanced stages of the disease. However, novel treatments are being introduced in the market and new ones are being developed. Targeted therapies and immunotherapy have brought about a bloom in the treatment of non-small cell lung cancer. Still we have to find ways to administer drugs in a more efficient and safe method. In the current review, we will focus on the administration of inhaled cisplatin based on published data.

Nebulization as a tool for photosensitizer delivery to the respiratory tract

To this day, any photosensitizers for the photodynamic treatment of pulmonary illnesses have been administered intravenously. There is, however, an intrinsic difficulty in reaching the target cells or bacteria in the respiratory system. Nebulization could overcome distribution problems and alleviate side effects by delivering the photosensitizers directly to the lungs. In this study, we evaluated the viability of three photosensitizers (indocyanine green, the chlorine Photodithazine, and the porphyrin Photogem) was evaluated comparatively in a jet nebulizer. Quantitative analysis was performed by looking at the droplet size, extent of nebulization, output over time and stability of the solutions. All of the tested photosensitizers were found to be adequately nebulized. We also demonstrated the delivery of indocyanine green to the pulmonary tract and its activation with infrared light in a murine model using extracorporeal detection of fluorescence. This was an important step toward clinical implementation of the extracorporeally illuminated photodynamic inactivation of pneumonia, recently demonstrated in vivo by this research group.

Production and characterization of bioaerosols for model validation in spacecraft environment

This study aimed to evaluate the suitability of two bioaerosol generation systems (dry and wet generation) for the aerosolization of microorganisms isolated from the International Space Station, and to calibrate the produced bioaerosols to fulfill the requirements of computational fluid dynamics model (CFD) validation. Concentration, stability, size distribution, agglomeration of generated bioaerosol and deposition of bioaerosols were analyzed. In addition, the dispersion of non-viable particles in the air was studied. Experiments proved that wet generation from microbial suspensions could be used for the production of well-calibrated and stabile bioaerosols for model validation. For the simulation of the natural release of fungal spores, a dry generation method should be used. This study showed that the used CFD model simulated the spread of non-viable particles fairly well. The mathematical deposition model by Lai and Nazaroff could be used to estimate the deposition velocities of bioaerosols on surfaces, although it somewhat underestimated the measured deposition velocities.

Methacholine Challenge: Comparison of Airway Responsiveness Produced by a Vibrating Mesh Nebulizer Versus a Jet Nebulizer

BACKGROUND

The latest methacholine challenge testing (MCT) guidelines published by the European Respiratory Society recommend the characterization of nebulizers before their use in clinics and research. Such investigations are necessary for accurately determining the provocative dose of methacholine causing a 20% fall in FEV₁ (PD₂₀) delivered by a given device. The standard English Wright (Wright) jet nebulizer recommended in the 1999 guidelines by the American Thoracic Society has become difficult to obtain and possesses some characteristics that complicate the calculation of dose delivery from this device (e.g. evaporation). Our objective was to determine if the Aerogen^® Solo (Solo) vibrating mesh nebulizer provides similar methacholine challenge test results compared to the currently used Wright jet nebulizer.

METHODS

Sixty mild-to-moderate asthmatics were studied across three research sites in a randomized crossover study. Both methacholine challenges were completed at least 24 hours apart within a 2-week period. Testing with the Wright device was performed as per the 2-minute tidal breathing protocol. The Solo study arm followed the same procedure except for a shorter inhalation time of 1 minute. The provocative concentration of methacholine causing a 20% fall in FEV₁ (PC₂₀) and the methacholine PD₂₀ were calculated following each methacholine challenge.

RESULTS

The geometric mean methacholine PC₂₀ values for the Solo and the Wright differed statistically (0.65 mg/mL vs. 2.58 mg/mL, respectively, p < 0.00001) and clinically. Between-nebulizer geometric mean methacholine PD₂₀ results are comparable by clinical standards [81.7 μg (Solo) vs. 64.7 μg (Wright)], although the slight difference in dose was statistically significant (p = 0.018).

CONCLUSIONS

The comparability of PD₂₀ values between the Solo and the Wright validates the importance of reporting airway responsiveness to methacholine in terms of dose and not concentration, as stressed in the latest testing guidelines. This finding along with several benefits associated with the Solo make it a promising nebulizer for performing MCT.

A modified nebulization modality versus classical ultrasonic nebulization and oxygen-driven nebulization in facilitating airway clearance in patients with acute exacerbation of chronic obstructive pulmonary disease: a randomized controlled trial

BACKGROUND

Ultrasonic nebulization (UN) and oxygen-driven nebulization (ON), two commonly used modalities for nebulization inhalation, are not ideally suitable for patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD).

METHODS

A total of 91 patients with AECOPD were randomized to three groups given different nebulization modalities: ON, UN, and ultrasonic nebulization with warming and oxygen (UNWO). The sputum clearance, lung function, changes in physiological measures such as peripheral oxygen saturation (SpO2) and tolerance to these nebulization modalities were recorded and compared among the three groups.

RESULTS

The time to the first expectoration was shorter and the sputum volume was larger after UN and UNWO than after ON (both P<0.01). Compared with pre-nebulization, SpO2 significantly increased (P<0.01) and the dyspnea decreased significantly (P<0.05) after UNWO. The SpO2 and dyspnea post-UNWO were significantly better than those post-UN (P<0.01, P<0.05), but not statistically different from those post-ON (both P>0.05). UNWO demonstrated significantly greater comfort and longer duration of nebulization than UN (P<0.01, P<0.05), but no significant differences in these respects from ON (both P>0.05). Forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and peak expiratory flow (PEF) decreased significantly after UNWO (P<0.05, P<0.01, and P<0.01, respectively).

CONCLUSIONS

UNWO may promote expectoration of sputum with fewer adverse reactions and a higher level of comfort than simple UN and ON. Therefore, it can be used as an adjuvant therapy for AECOPD patients.

Early postnatal, but not late, exposure to chemical ambient pollutant 1,2-naphthoquinone increases susceptibility to pulmonary allergic inflammation at adulthood

High diesel exhaust particle levels are associated with increased health effects; however, knowledge on the impact of its chemical contaminant 1,2-naphthoquinone (1,2-NQ) is limited. We investigated whether postnatal and adult exposures to 1,2-NQ influence allergic reaction and the roles of innate and adaptive immunity. Male neonate (6 days) and adult (56 days) C57Bl/6 mice were exposed to 1,2-NQ (100 nM; 15 min) for 3 days, and on day 59, they were sensitized and later challenged with ovalbumin (OVA). Airway hyper-responsiveness (AHR) and production of cytokines, immunoglobulin E (IgE) and leukotriene B4 (LTB4) were measured in the airways. Postnatal exposure to 1,2-NQ activated dendritic cells in splenocytes by increasing expressing cell surface molecules (e.g., CD11c). Co-exposure to OVA effectively polarized T helper (Th) type 2 (Th2) by secreting Th2-mediated cytokines. Re-stimulation with unspecific stimuli (PMA and ionomycin) generated a mixed Th1 (CD4(+)/IFN-γ(+)) and Th17 (CD4(+)/IL-17(+)) phenotype in comparison with the vehicle-matched group. Postnatal exposure to 1,2-NQ did not induce eosinophilia in the airways at adulthood, although it evoked neutrophilia and exacerbated OVA-induced eosinophilia, Th2 cytokines, IgE and LTB4 production without affecting AHR and mast cell degranulation. At adulthood, 1,2-NQ exposure evoked neutrophilia and increased Th1/Th2 cytokine levels, but failed to affect OVA-induced eosinophilia. In conclusion, postnatal exposure to 1,2-NQ increases the susceptibility to antigen-induced asthma. The mechanism appears to be dependent on increased expression of co-stimulatory molecules, which leads to cell presentation amplification, Th2 polarization and enhanced LTB4, humoral response and Th1/Th2 cytokines. These findings may be useful for future investigations on treatments focused on pulmonary illnesses observed in children living in heavy polluted areas.

Experimentation with inhaled bronchodilators and corticosteroids

BACKGROUND

Inhaled bronchodilators and corticosteroids have been used for decades with different production systems.

MATERIALS AND METHODS

The following jet-nebulizers: (a) Invacare, (b) Sunmist, (c) Maxineb and ultrasound nebulizers: (a) GIMA, (b) OMRON and (c) EASY NEB II were used as production systems. The jet-nebulizers were used with different residual cups and volume filling, while the ultrasound nebulizers with different volume fillings and face mask versus inlet.

RESULTS

Inhalation and ultrasound process detect significant differences between the factors and interactions considered, but each technique follows a specific pattern of magnitude effect. Thus the inhaled mechanism ranks the factor effects in decreasing order: residual cup>drug>nebulizer>loading (2, 3, 4 ml) and also drug>residual cup>nebulizer (loading 8 ml). The ultrasound mechanism orders as follows: nebulizer>drug>loading. In fact, varying micro environmental conditions created during the performance of the devices in both processes alternate the magnitude of factor significance allowing for unique capacities.

CONCLUSIONS

PULMICORT, MAXINEB, design cup J and loading 6 ml are the best options for the inhaled process. Optimal combinations are provided by FLIXOTIDE and cup B and also by MAXINEB and cup J. The incorporation of large residual cups suggests one out of six drugs, the SUNMIST nebulizer and design D as the best choices. Ultrasound performance informs for other optimal conditions: ZYLOREN, MAXINEB, 4 ml load and MAXINEB×loading 4 ml.

Further experimentation of inhaled; LANTUS, ACTRAPID and HUMULIN with todays' production systems

BACKGROUND

Several aerosol production systems have been used for aerosol insulin production. However; since the first studies several new models of jet-nebulizers and ultrasound nebulizers have been introduced in the market.

MATERIALS AND METHODS

Three different models of jet-nebulizers (different brands, same properties) and three different ultrasound nebulizers (different brands, same properties). Six residual cups (2 small ≤ 6 ml and 3 large ≤ 8 ml) were used for the jet-nebulizers. The ultrasound nebulizers were used with their facemasks or with their inlets which were included in the purchase package.

RESULTS

Ultrasound nebulizers; LANTUS produces by far the lowest mean droplets (2.44) half the size of the other two drugs (4.43=4.97). GIMA nebulizer is the most efficient producing one third of the droplet size of SHIMED and one second of EASYNEB (2.06<3.15<6.62). Finally, the 4 ml loading concentration is more suitable for supporting the production of smaller droplets (3.65<4.24). Drugs and nebulizers act interactively yielding very large droplets when ACTRAPID and HUMULIN are administered in joint with SHIMED nebulizer (9.59=7.72). Jet-nebulizers; HUMULIN again is the least preferred insulin since it hardly reaches the low but equal performance of others at the loading level of 6 ml. Residual cups E and B produce uniquely lower mean droplets at loading level 6.

CONCLUSIONS

Ultrasound nebulizers; the best suggested combination should be LANTUS insulin, GIMA nebulizer administered at loading dose of 4 ml jet-nebulizers. A global review can give the best combination: the lowest mean droplets are produced when the drugs LANTUS (mostly) and ACTRAPID are administered, applying the SUNMIST nebulizer in concert with residual cup B at loading levels of 6 ml.

Solid Lipid Nanoparticles (SLN) and Nanostructured Lipid Carriers (NLC) for pulmonary application: a review of the state of the art

Drug delivery by inhalation is a noninvasive means of administration that has following advantages for local treatment for airway diseases: reaching the epithelium directly, circumventing first pass metabolism and avoiding systemic toxicity. Moreover, from the physiological point of view, the lung provides advantages for systemic delivery of drugs including its large surface area, a thin alveolar epithelium and extensive vasculature which allow rapid and effective drug absorption. Therefore, pulmonary application is considered frequently for both, the local and the systemic delivery of drugs. Lipid nanoparticles - Solid Lipid Nanoparticles and Nanostructured Lipid Carriers - are nanosized carrier systems in which solid particles consisting of a lipid matrix are stabilized by surfactants in an aqueous phase. Advantages of lipid nanoparticles for the pulmonary application are the possibility of a deep lung deposition as they can be incorporated into respirables carriers due to their small size, prolonged release and low toxicity. This paper will give an overview of the existing literature about lipid nanoparticles for pulmonary application. Moreover, it will provide the reader with some background information for pulmonary drug delivery, i.e., anatomy and physiology of the respiratory system, formulation requirements, application forms, clearance from the lung, pharmacological benefits and nanotoxicity.

Vibrating-mesh nebulization of liposomes generated using an ethanol-based proliposome technology

This is the first study that evaluates the influence of the compartmental design of the micropump Aeroneb Go nebulizer and the viscosity of a proliposome hydration medium on vibrating-mesh aerosolization of liposomes. Ethanol-based proliposomes comprising soya phosphatidylcholine and cholesterol (1:1 mole ratio) were hydrated by using isotonic NaCl (0.9%) or sucrose (9.25%) solutions to generate liposomes that entrapped approximately 61% of the hydrophilic drug, salbutamol sulphate. Liposomes were aerosolized by the nebulizer to a two-stage impinger. For both formulations, the aerosol mass output was higher than the phospholipid output, indicating some accumulation of large liposomes or liposome aggregate within the nebulizer. Using NaCl (0.9%) solution as the dispersion medium, aerosol droplet size was much smaller and aerosol mass and phospholipid outputs were higher. This was attributed to the lower viscosity of the NaCl solution, resulting in a reduced retention of the aerosols in the "trap" of the nebulizer. For the entrapped salbutamol sulphate, although the "fine particle fraction" was relatively high (57.44%), size reduction of the liposomes during nebulization caused marked losses of the drug originally entrapped. Overall, liposomes generated from proliposomes when using this nebulizer showed high nebulization output and small droplet size. However, further work is required to reduce the losses of the originally entrapped drug from liposomes.

Development of nano alpha-ketoglutarate nebulization formulation and its pharmacokinetic and safety evaluation in healthy human volunteers for cyanide poisoning

Development of nano alpha-ketoglutarate (A-KG) nebulization formulation for neutralization of inhaled cyanide ion toxicity. Objectives of the present study were to (a) develop a novel A-KG nebulization formulation against cyanide poisoning, particularly hydrogen cyanide gas (b) validate its respiratory fraction in vitro and in vivo, and (c) create its pharmacokinetic data in human volunteers. The formulation was optimized on the basis of particle size of aerosolized droplets after nebulization in 6 volunteers. Gamma scintigraphy was used to quantify total and regional lung deposition of nebulized A-KG after radiolabeling it with Technetium-99m. The formulation was optimized using 30% ethanol-saline with particle size in the range of 300-500 nm. In vitro and in vivo studies showed that drug nebulization resulted in a significant respirable fraction of 65 ± 0.6% with whole lung deposition of 13 ± 1%. Human pharmacokinetic data was derived in 6 healthy human volunteers with peak serum concentration (C(max)) of 39 ± 3 μg/ml, while the area under curve (AUC) after inhalation was 376 ± 23 μg × h/ml indicating that the drug was rapidly and completely absorbed when targeted directly to lungs. Significant lung deposition of A-KG was achieved with the developed formulation. The formulation appears to have several advantages, including the potential of neutralizing inhaled CN(-) ions in the lungs themselves. It is a safe and efficacious procedure, suitable for hospital or ambulance use in accidental cyanide poisoning cases, or as a preventive approach for fire-rescue teams.

Characterization of a nose-only inhalation exposure system for hydrocarbon mixtures and jet fuels

A directed-flow nose-only inhalation exposure system was constructed to support development of physiologically based pharmacokinetic (PBPK) models for complex hydrocarbon mixtures, such as jet fuels. Due to the complex nature of the aerosol and vapor-phase hydrocarbon exposures, care was taken to investigate the chamber hydrocarbon stability, vapor and aerosol droplet compositions, and droplet size distribution. Two-generation systems for aerosolizing fuel and hydrocarbons were compared and characterized for use with either jet fuels or a simple mixture of eight hydrocarbons. Total hydrocarbon concentration was monitored via online gas chromatography (GC). Aerosol/vapor (A/V) ratios, and total and individual hydrocarbon concentrations, were determined using adsorbent tubes analyzed by thermal desorption-gas chromatography-mass spectrometry (TDS-GC-MS). Droplet size distribution was assessed via seven-stage cascade impactor. Droplet mass median aerodynamic diameter (MMAD) was between 1 and 3 mum, depending on the generator and mixture utilized. A/V hydrocarbon concentrations ranged from approximately 200 to 1300 mg/m(3), with between 20% and 80% aerosol content, depending on the mixture. The aerosolized hydrocarbon mixtures remained stable during the 4-h exposure periods, with coefficients of variation (CV) of less than 10% for the total hydrocarbon concentrations. There was greater variability in the measurement of individual hydrocarbons in the A-V phase. In conclusion, modern analytical chemistry instruments allow for improved descriptions of inhalation exposures of rodents to aerosolized fuel.

Recognition and surveillance of occupational asthma: a preventable illness with missed opportunities

Occupational asthma is common, disabling and costly, and it is often difficult to diagnose. Incidence statistics are consequently unreliable, and there are formidable difficulties in recognizing and managing what should be a preventable illness. The opportunities have largely been missed. The author offers a personal view of what, ideally, should be done--recognizing that at present the ideal is not readily practical. Always consider the possibility of an occupational cause at the time adult-onset asthma is first recognized-the probability of this is of the order 9-15%. Do not prescribe treatment unless this possibility is remote or the asthma is life-threatening. If the possibility is not remote seek immediate advice from a specialized centre, without prescribing masking medication and without curtailing usual work practice. The specialized referral centre should place the accurate measurement of airway responsiveness at the centre of investigatory strategies. A return-to-work study, monitored by serial measurements of airway responsiveness and ventilatory function, provides adequate objective evidence for diagnosis in most cases. When a novel cause is suspected, specific inhalation provocation testing with the particular agent in the specialized centre is desirable. Regular competent surveillance is necessary in high-risk occupational environments; this should include environmental monitoring, the detection of relevant new symptoms, spirometry measurements, serum antibody studies (where available) and a robust protocol for managing inevitable failed attendances.

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.

Laboratory methods for assessing vaccine potency retained in aerosol outputs from nebulizers: application to World Health Organization measles aerosol project

BACKGROUND

Laboratory methods for measuring vaccine potency of nebulized aerosol are required to support clinical trials of measles aerosol vaccination.

METHODS

Measles vaccine containing the Edmonston Zagreb virus strain was reconstituted in sodium fluoride as tracer and nebulized from three devices. Emitted aerosol was collected using an impinger. Aliquots were removed from the impinger chamber for vaccine virus plaque assay and for fluoride measurement to determine aerosol output.

RESULTS

Vaccine potency retention results were adjusted to take into account the effect of aerosol output on estimates. Adjusted potency of nebulized vaccine ranged from 88% to 102%.

CONCLUSIONS

New laboratory methods to measure aerosol vaccine potency retention were reliable and accurate. The results demonstrated that Edmonston Zagreb vaccine remains robust during aerosolisation and imply that this is a viable candidate for further evaluation in the measles aerosol project.

Factors Controlling Particle Size during Nebulization of DNA–Polycation Complexes

Pulmonary gene therapy has the potential to treat or cure respiratory diseases such as cystic fibrosis. Much work has focused on the delivery of genes to the lung using viral vectors with varying degrees of success. Viral vectors are problematic and undesirable for use in the lung because they can provoke an acute immune response. This study has focused on the characterization of nonviral, polymer-based gene vectors for use with nebulizers. Calf thymus DNA has been used as a model, and was complexed with each of the three polycations; 22 kDa linear polyethyleneimine, 25 kDa branched polyethyleneimine, and 29.5 kDa polylysine using water, glucose solution, and phosphate-buffered saline (PBS) as carrier liquids. Fourier transform infrared spectroscopy has shown that the DNA retains the B form during the complex formation. The complexes prepared at N:P ratios of 10, have been nebulized using a vibrating plate nebulizer and the particle size and Zeta potentials measured before and after nebulization. The particle size distributions of the DNA complexes prepared in water and glucose solution were unimodal before and after nebulization with a small increase in particle size following nebulization. Choice of complexing polymer is shown to have only a small effect on particle size with the dominant effect coming from the ionic character of the dispersion fluid. Complexes prepared in PBS, although originally unimodal, showed pronounced agglomeration on nebulization. With all polymers in water or glucose solution, the Zeta potential increases after nebulization, but with PBS as the carrier liquid the potential falls and is clearly associated with the observed agglomeration. Gel electrophoresis shows that the complexing polymers protect the DNA through the nebulization process in all cases.

The influence of fluid physicochemical properties on vibrating-mesh nebulization

In this study, the effect of fluid physicochemical properties and the vibrating-mesh mechanism on the aerosols generated from vibrating-mesh nebulizers have been evaluated using fluids having a range of viscosity, surface tension and ion concentration. Two nebulizers were investigated: the Omron MicroAir NE-U22 (passively vibrating) and the Aeroneb Pro (actively vibrating) mesh nebulizers. For both devices, the total aerosol output was generally unaffected by fluid properties. Increased viscosity or ion concentration resulted in a decrease in droplet volume median diameter (VMD) and an increase in fine particle fraction (FPF). Moreover, increased viscosity resulted in prolonged nebulization and reduced output rate, particularly for the Omron nebulizer. Both nebulizers were unsuitable for delivery of viscous fluids since nebulization was intermittent or completely ceased at >1.92cP. The presence of ions reduced variability particularly for the Aeroneb Pro nebulizer. No clear effect of surface tension was observed on the performance of nebulizers employing a vibrating-mesh technology. However, when viscosity was low, reduced surface tension seemed advantageous in shortening the nebulization time and increasing the output rate, but for the Omron nebulizer this also increased the droplet VMD and decreased the FPF. This study has shown that vibrating-mesh nebulization was highly dependent on fluid characteristics and nebulizer mechanism of operation.

The customised electronic nebuliser: a new category of liquid aerosol drug delivery systems

Inhalation of aerosols is the preferred route of administration of pharmaceutical compounds to the lungs when treating various respiratory diseases. Inhaled antibiotics, hormones, peptides and proteins are potential candidates for direct targeting to the site of action, thus minimising systemic absorption, dilution and undesired side effects, as much lower doses (as low as a fiftieth) are sufficient to achieve a similar therapeutic effect, compared with oral administration. A quick relief from the symptoms and a good tolerance are the main advantages of aerosol therapy. A new class of electronic delivery device is now starting to enter the market. The eFlow electronic nebuliser (PARI GmbH, Germany) provides improved portability and, in some instances, cuts treatment time to only a fraction of what has been experienced with current nebulised therapy. Drug formulations and the device can be mutually adapted and matched for optimal characteristics to meet the desired therapeutic target. Reformulation of known and proven compounds in a liquid format are commercially attractive as they present a relatively low development risk for potential drug candidates and, thus, have become a preferred pathway for the development of new inhalation products.

Reproducibility and validity of a Yan-style portable citric acid cough challenge

Although many different methods of measuring cough reflex sensitivity have been published, few are simple enough to use outside of a hospital or laboratory environment. The aim of this study was to develop a simple, quick, and portable cough challenge, assess its reproducibility, and compare its results with those measured by an existing established hospital protocol. Twenty-five volunteers performed cough challenges based on an established hospital dosimeter protocol, and, on a separate occasion, by a protocol inhaling citric acid from DeVilbiss 40 hand-held nebulisers (citric acid concentrations of 10-3000 mM). Reproducibility of the hand-held cough challenge was assessed in 11 volunteers. Cough thresholds were consistently higher by the hand-held method than by the hospital dosimeter method. The geometric mean citric acid concentrations causing two coughs (threshold D2) were 3.14 and 2.77 log mM, respectively (p<0.001). The geometric mean (95% CI) difference between the tests was 0.51 log mM (0.18-0.83) of the average of the two values. Cough D2 thresholds attained by the two techniques did, however, show significant correlation (r=0.95, p<0.0001). The coefficient of repeatability for the hand-held method was 0.40 log mM. Administering citric acid from DeVilbiss 40 hand-held nebulisers offers a rapid, portable, and reproducible cough challenge in healthy volunteers. The results correlate well with an existing Mefar dosimeter challenge, but give two to three times greater cough thresholds.

Comparison of Lung Deposition in Two Types of Nebulization

BACKGROUND

So-called intrapulmonary percussive ventilation (IPV), frequently coupled with a nebulizer, is increasingly used as a physiotherapy technique; however, its physiologic and clinical values have not been rigorously assessed.

STUDY OBJECTIVE

To compare in vitro and in vivo characteristics of the nebulizer of the IPV device (Percussionaire; Percussionaire Corporation; Sandpoint, ID) with those of standard jet nebulization (SST) [SideStream; Medic-Aid; West Sussex, UK].

DESIGN

Aerodynamic particle size was studied by an cascade impactor. The deposition of (99m)Tc-diethylenetriaminepenta-acetic acid was measured in 10 healthy subjects by tomoscintigraphy during spontaneous breathing with both nebulizers.

MEASUREMENTS AND RESULTS

The mass median aerodynamic diameter (0.2 micro m vs 1.89 micro m for IPV and SST, respectively) and the fine-particle fraction (16.2% vs 67.5%, respectively) were significantly smaller with IPV. In vivo, respiratory frequency (RF) was lower with the IPV device (10.1 +/- 3.4 breaths/min vs 14.6 +/- 3.4 breaths/min, p = 0.002). Whole-body deposition was significantly higher with IPV (15.63% vs 9.31%), but it was due to a higher extrapulmonary deposition. Although intrapulmonary deposition (IPD) was not different with both devices (4.20% for SST vs 2.49% for IPV), it was much more variable with IPV, compared to SST. The penetration index into the lung was higher with IPV than SST when normalized for RF (0.045 +/- 0.018 breaths/min vs 0.026 +/- 0.013 breaths/min, p = 0.007).

CONCLUSION

The two techniques showed comparable lung deposition despite a large difference in particle size. However, IPV IPD was too variable and thus too unpredictable to recommend its use for drug delivery to the lung.

Factors affecting aerosol performance during nebulization with jet and ultrasonic nebulizers

Nebulization of aqueous solutions is a convenient delivery system to deliver drugs to the lungs because it can produce droplets small enough to reach the alveolar region. However, the droplet size might be affected by the changes in the temperature and the concentration of the nebulizing solution in the reservoir during nebulization. In this study, the changes in the droplet size over the nebulization time using a PariBoy air-jet and a Multisonic ultrasonic nebulizer have been studied. The findings were related to changes in the temperature, concentration, surface tension, viscosity and saturated vapour pressure of the nebulizing solution. By using the jet nebulizer, an increase in the droplet size followed by a decrease has been observed. This observation could be attributed to the approx. 7 degrees C reduction of the temperature during the first 2 min in the jet nebulizer reservoir which increased the viscosity of the nebulizing solution. After this initial period of time, the increasing drug concentration induced a reduction of the surface tension and, consequently, a decrease in the droplet size. However, with the ultrasonic nebulizer a temperature increase of approx. 20 degrees C during the first 6 min in the nebulizing solution was observed leading to a decrease in droplet size, viscosity and surface tension and an increasing saturated vapour pressure. This again led to smaller average droplet sizes.

An investigation of in vitro/in vivo correlations for salbutamol nebulized by eight systems

The choice of a nebulized system for a patient usually depends on the equipment available. To date, there is limited guidance on the selection and use of a nebulizer. We have conducted in vitro tests described within the draft European Standard for Nebulisers (BSEN13544-1; CEN) and correlated these to in vivo pharmacokinetic performance of relative lung and systemic deposition in healthy volunteers. Eight nebulizer systems have been tested. The in vitro analysis used the recommended CEN methods to quantify the total dose available for inhalation as well as the size distribution from which the respirable dose was determined. The draft European Standard methods were slightly modified to use salbutamol rather than a fluoride tracer. For the in vivo study, nine volunteers provided urine samples after 30 min and then pooled for 24 h after the start of each nebulized dose (2.5 mg of salbutamol). Amounts of salbutamol and its metabolite excreted in the urine samples were determined. There was a significant (p = 0.02) correlation between the in vitro respirable dose and the amount of salbutamol excreted in the urine 30 min after the start of nebulization (relative bioavailability of salbutamol to the lung). Also, there was a significant (p < 0.001) correlation between the in vitro dose available for inhalation and the total amount of salbutamol and its metabolites excreted over the 24 h after the start of nebulization (relative bioavailability of salbutamol to the body). The results demonstrate that in vivo/in vitro correlations exist and warrant further investigations. The in vitro methods require further validation with in vivo correlations using patients with different severities of airway obstruction.

The salt output of a nebulizer--a comparison between two nebulizer types

The output of a nebulizer is generally defined as its weight loss during 1 min of nebulization. This mass output includes the weight loss due to evaporation of the solution required to moisten the dry air that is fed through the nebulizer. In order to compare results obtained from studies using different nebulizers we introduce the salt output as the amount of the solution that actually leaves the liquid phase as droplets and not by evaporation. The performance characteristics of a standard jet nebulizer (MA2) and a Sidestream jet neublizer were compared. Mass output was determined at different methacholine concentrations. Salt output was assessed by analysing the remaining salt in the nebulizers after 1 min of nebulization. Overall system performance in terms of forced expiratory volume in 1 sec (FEV1) reduction after 1 min of exposure to individually selected concentrations of methacholine were studied in 15 healthy, non-smoking subjects. Both nebulizer types showed a moderate linear increase of mass output with methacholine concentration. The efficiency coefficient, the quotient between salt output and mass output, was found to be 0.93 and 0.75 for the MA2 and Sidestream nebulizer respectively. These findings were explained by differences in airflow through, and temperature inside, the nebulizers. The salt output of the nebulizers proved to be better correlated to the FEV1-reduction following methacholine inhalation than did the mass output. The relative amount of the salt output that adhered to the acrylic walls of the Sidestream nebulizer drying tower was found to be 9%. We conclude that it is more appropriate to use salt output than mass output as a nebulizer performance descriptor. The study also shows the importance of determining nebulizer system performance under conditions as similar to true provocations as possible.

The conventional ultrasonic nebulizer proved inefficient in nebulizing a suspension

A study was undertaken to compare the amount of nebulized budesonide suspension and nebulized terbutaline sulphate solution inhaled by healthy adult subjects when conventional jet and ultrasonic nebulizers were used. Ten healthy subjects (5 male; age range, 16-52 years) used two conventional nebulizers: the Spira Elektro 4 jet nebulizer (Respiratory Care Center, Hämeenlinna, Finland) and the Spira Ultra ultrasonic nebulizer (Respiratory Care Center) in a breath-synchronized mode with each drug. The amount of drug inhaled, the inhaled mass, was defined as the amount of drug deposited on a filter between the inspiratory port of the nebulizer and the mouthpiece. The amount of budesonide and terbutaline sulphate was determined by reversed-phase high-performance liquid chromatography. Single-dose respules were used (0.5 mg of budesonide and 5.0 mg of terbutaline sulphate), and nebulization time up to the defined gravimetric output was recorded. The inhaled mass of budesonide varied depending on the nebulizer used, whereas the inhaled mass of terbutaline was unaffected by the choice of nebulizer. The median inhaled mass of budesonide was 31.4% of the nominal dose (i.e., dose of drug in the respule per label claim) with the Spira Elektro 4 and 9.9% with the Spira Ultra, whereas the median inhaled mass of terbutaline was 50% with the Spira Elektro 4 and 52% with the Spira Ultra. It appears that a suspension is generally more difficult to nebulize than a solution and that the budesonide suspension should not be used in conventional ultrasonic nebulizers.

Characterization of heparin aerosols generated in jet and ultrasonic nebulizers

Inhaled heparin has been used for asthma treatment, but results have been inconsistent, probably due to highly varying lung doses. We determined the output per unit time and the particle size distributions of sodium heparin, calcium heparin, and low molecular weight (LMW) heparin formulations in five concentrations from Sidestream jet nebulizers (Medic-Aid, Bognor Regis, England) and an Ultraneb 2000 ultrasonic nebulizer (DeVilbiss, Langen, Germany). We also determined the inhaled mass and the estimated respirable mass for some combinations. For the jet nebulizer, output per minute increased with increasing concentration and flow rate, and particle size decreased from 3.64 to 2.01 microns (mass median diameter [MMD]). The percentage of particles less than 3 microns ranged from 41% to 74%. For the ultrasonic nebulizer, maximum output per minute was achieved at a concentration of 7000 i.u./mL; this maximum depended upon the viscosity and temperature of the solution. MMD was independent of formulation, temperature, or concentration and ranged from 5.61 to 7.03 microns. Sodium heparin/calcium heparin in a concentration of 20,000 i.u./mL in the jet nebulizer driven at 10 L/min produced the highest dose of heparin capable of reaching the lower respiratory tract. Mass balance was determined for these combinations with the jet nebulizer run until visible aerosol generation ceased. Of a loading dose of 80,000 i.u. of heparin, 45,000 i.u. remained in the dead space of the nebulizer, 20,000 i.u. was deposited on the exhalation filter, and 15,000 i.u. was captured on the inhalation filter (inhaled mass). This corresponds to a respirable mass of 10,000 i.u. of heparin with a high probability of reaching the lower respiratory tract in normal healthy adults.

Acute effects of nebulised epoprostenol in pulmonary hypertension due to systemic sclerosis

Pulmonary hypertension often has a lethal outcome in systemic sclerosis and the treatment is challenging. Epoprostenol is a potent pulmonary vasodilator and its efficacy has been demonstrated when delivered by the intravenous and aerosolized routes. We report the haemodynamic and functional benefits of epoprostenol administered by inhalation to a spontaneously breathing patient with partially reversible pulmonary hypertension due to systemic sclerosis. Aerosolized epoprostenol, equivalent to the maximum tolerated intravenous dose (31.2 micrograms), produced a 58% fall in pulmonary vascular resistance, increased the cardiac output by 42% and improved functional performance by one MET (3.5 ml kg-1 min-1 of oxygen uptake) without any significant side-effects. Selective distribution of epoprostenol by the inhaled route may offer a new strategy for treatment of pulmonary hypertension.

Aerosolization of cationic lipid:pDNA complexes--in vitro optimization of nebulizer parameters for human clinical studies

Previously, we have described the optimization of the aerosol delivery of a nonviral gene therapy vector to the lungs of rodents (Eastman et al., 1997b). Although aerosolizing cationic lipid:pDNA complexes into a whole-body exposure chamber resulted in high levels of reporter gene expression in the lungs of BALB/c mice, the conditions employed were not optimal for the delivery of lipid:pDNA complexes to the lungs of human patients. That is, the consumption rate of the material in the nebulizer, and thus the delivery time, were very slow and the aerosol was delivered in a continuous flow. Here we describe in vitro experiments used to develop a cationic lipid:pDNA aerosol with characteristics more suitable for delivery to the lungs of humans, as a necessary prerequisite for conducting a clinical study with human cystic fibrosis patients. Using cascade impactors and all-glass impingers, we have screened several commercially available nebulizers for their ability to deliver intact, respirable, active lipid:pDNA complexes in the shortest time possible, and have identified the Pari LC Jet Plus nebulizer as the optimal nebulizer that meets these criteria. Using this nebulizer in an intermittent mode to mimic breath actuation, consumption rates of approximately 0.6 ml/min of the cationic lipid:pDNA complexes (6 mM cationic lipid:8 mM pDNA) were obtained. The plasmid DNA remained intact and the complexes were shown to maintain activity throughout the nebulization run. Based on measurements of the nebulized dose and the mass median aerodynamic diameter, we calculate a delivered dose of approximately 22 micromol (7.2 mg) of pDNA for each 8 ml of cationic lipid:pDNA complex aerosolized to the lungs of a human patient. This dose should be sufficient to test the clinical efficacy of cationic lipid-mediated gene delivery for the treatment of cystic fibrosis.

The choice of jet nebulizer, nebulizing flow, and addition of albuterol affects the output of tobramycin aerosols

The use of inhaled antibiotics in the treatment of cystic fibrosis has become widespread despite controversy in the literature as to the appropriate dosing regimen and its effectiveness. This study compared two tobramycin (T) preparations (one with and one without the addition of albuterol) using two different jet nebulizers in order to determine if drug output would be affected. Using calibrated flows from a dry compressed gas source of 6 and 8 L/min as well as a specific compressor (Pulmo-Aide), the Hudson 1720 nebulizer was compared with the newer disposable Hudson 1730. The albuterol preparation used in this study was the Ventolin (albuterol) Respirator Solution (VRS). The nebulizers were charged with (1) 2 mL T (80 mg/2 mL) with 0.5 mL VRS (5 mg/mL) and normal saline solution to make the total nebulizer charge of 3 or 4 mL, or (2) 2 mL T and either 1 or 2 mL normal saline solution. A laser diffraction analyzer (Malvern 2600) was used to determine the aerosol particle size distribution. From the distribution, the respirable fraction, which is the fraction of aerosol that could enter and remain in the lungs, was calculated. For all solutions and each particular flow, the Hudson 1730 had a larger respirable fraction of T. The addition of VRS lowered the surface tension of the solution in the nebulizer and resulted in a greater output of T. This effect was most apparent for the 3-mL volume fills of the Hudson 1720. The greatest differences were between the 3-mL nebulizer charges of T using the Hudson 1720 driven by a flow of 6 L/min, which produced 8 mg of T in the respirable fraction, compared with 35 mg produced by the Hudson 1730 driven by a flow of 8 L/min. These results suggest that different nebulizers, different nebulizer solutions, and different techniques of nebulization may result in very different amounts of T aerosol output in the respirable fraction.

Measuring nebulizer output. Aerosol production vs gravimetric analysis

STUDY OBJECTIVES

The function of jet nebulizers has been measured traditionally by gravimetric methods, i.e., by weighing nebulizers before and after nebulization. Newer techniques measure aerosol output directly by analyzing aerosolized drug or tracer, i.e., radioactive 99mTc. Because of evaporation, the equivalence of these methods is uncertain. The aim of this study was to determine if the gravimetric method is an accurate measure of aerosol production under different conditions of aerosol generation (i.e., nebulizer type, flow rate, pressure, volume fill, and concentration of solution used to nebulize a drug).

METHODS

In the first phase of the study, we measured the aerosol output of nine commercially available jet nebulizers (AvaNeb; Up-Draft-Hudson RCI; Cirrus-Intersurgical Inc; DeVilbiss 646-DeVilbiss; Powermist-Hospitak, Inc; Respirgard II-Marquest Medical Products; Seamless-Seamless/Dart Respiratory; Salter; Salter Labs; Airlife-Baxter Health Care) run under commonly used conditions (2.5 mL volume fill, 2.0 mL normal saline solvent, 0.5 mL albuterol, flow of 6 L/min, and pressures averaging 15.0 +/- 2.3 [mean +/- SD] pounds per square inch [on the] gauge [psig] provided by a DeVilbiss PulmoAide compressor) with simultaneously measured gravimetrics and filtered radioactivity. Each nebulizer was run to dryness with data acquired every 2 min. The change in the weight of the nebulizer and radioactivity captured on the filter were expressed as percentages of the total in the nebulizer solution. In the second phase of the study, the experiments were repeated using the same nebulizers with a volume fill of 5 mL (diluted to half normal saline solution plus albuterol), flow of 10 L/min, and pressures of 35.6 +/- 8.8 psig.

RESULTS

The cumulative (sum of all 2-min runs) weight loss for each individual nebulizer ranged from 25.00 to 64.55% and cumulative aerosol captured varied from 12.63 to 38.76%. While different, the weight loss and aerosol captured were closely correlated (y = -0.62 + 0.62x; r = 0.961, p < 0.0001). Changing volume fill and concentration of solvent did not affect this correlation (p = 0.921 and 0.373, respectively). However, changing flow from 6 L/min to 10 L/min significantly (p = 0.02) affected the relationship (y = -3.80 + 0.83x; r = 0.969, p < 0.001).

CONCLUSIONS

When compared with direct methods such as filtering generated particles, the gravimetric method of assessing nebulizer function overestimates aerosol output by 1.8 +/- 0.18 times, presumably because of the loss of solvent during nebulization. However, the relationship between methods is predictable and appears unaffected by changing the type of nebulizer, volume fill, and concentration of solvent. Changes in nebulizer flow and pressure significantly affected the correlation. Gravimetric methods can be used as simple and convenient screening techniques for comparing jet nebulizers under a wide range of experimental conditions.