Reconciliation of Cascade Impaction during Wet Nebulization

Humidified and Heated Cascade Impactor for Aerosol Sizing

Aerosol sizing is generally measured at ambient air but human airways have different temperature (37°C) and relative humidity (100%) which can affect particle size in airways and consequently deposition prediction. This work aimed to develop and evaluate a new method using cascade impactor to measure particle size at human physiological temperature and humidity (HPTH) taking into account ambient air conditions. A heated and humidified trachea was built and a cascade impactor was heated to 37°C and humidified inside. Four medical aerosols [jet nebulizer, mesh nebulizer, Presurized Metered Dose Inhaler (pMDI), and Dry Powder Inhaler (DPI)] under ambient conditions and at HPTH were tested. MMAD was lower at HPTH for the two nebulizers; it was similar at ambient conditions and HPTH for pMDI, and the mass of particles smaller than 5 μm decreased for DPI at HPTH (51.9 vs. 82.8 μg/puff). In conclusion, we developed a new method to measure particle size at HPTH affecting deposition prediction with relevance. In vivo studies are required to evaluate the interest of this new model to improve the precision of deposition prediction.

Capturing the efficiency of vibrating mesh nebulizers: minimizing upper airway deposition

BACKGROUND

Vibrating mesh devices are portable nebulizer systems with reported high efficiency. Losses occur during expiration, and particle size distributions vary. We describe an aerosol chamber designed to capture and condition aerosols from a typical vibrating mesh nebulizer, the Omron U22. The goal was to improve inhaled mass (IM) and respirable fraction (RF) and shorten treatment time.

METHODS

With test solutions of radiolabeled saline, we characterized the Omron U22 (three examples) vibrating mesh nebulizer measuring aerosol output with different breathing patterns, with and without manual breath synchronization. Particle size distributions were measured by cascade impaction as a "standing cloud" and during ventilation with a piston respirator. IM (percentage of nebulizer charge), respirable mass (RM), particle size distribution, and breathing time were measured with and without use of the chamber. Breathing patterns were designed to simulate tidal breathing with a "COPD" (chronic obstructive pulmonary disease) pattern (450 mL, rate 15, duty cycle 0.35) and "slow and deep" breathing for maximal lung deposition (1,500 mL, rate 5, duty cycle 0.70). Patterns of deposition were confirmed in a human volunteer using a gamma camera.

RESULTS

IM was significantly affected by breathing pattern and averaged 30.0±2.91% and 53.9±7.99% for COPD and slow and deep patterns, respectively. With the chamber, IM was less sensitive to breathing pattern (57.4±6.97%, 57.9±4.69%, respectively). Particle size distributions varied widely between devices and were markedly affected by both ventilating the device and addition of the chamber. With the chamber, RF and RM increased, and differences in particle size distributions between individual devices were minimized. Compared with breath synchronization, treatment time was reduced. Gamma camera images revealed reduced upper airway deposition consistent with predictions from in vitro cascade distributions.

CONCLUSIONS

Our prototype chamber allowed for capture and conditioning of nebulized aerosol by mixing with room air and removal of large particles by impaction, providing better control of IM, RF, RM, and lung deposition, without the need for breath synchronization.

Omron NE U22: Comparison between vibrating mesh and jet nebulizer

BACKGROUND

To overcome the limitations of conventional jet nebulizers, vibrating mesh technology has been commercialized. The present article is designed to address clinically relevant issues for routine aerosol therapy for a vibrating mesh nebulizer, the Omron NE U22, compared to traditional jet nebulizers.

METHODS

Inhaled mass (IM), residual activity, particle distribution, including mass median aerodynamic diameter (MMAD) and run time, were determined for radiolabeled albuterol (2.5 mg/3 mL). Omron NE U22, Pari LC Plus, and Sidestream nebulizers were tested. The Omron was tested in two positions, tilted and horizontal. Finally robustness of the Omron NE U22 was determined by repeating treatment 60 times. All Omron experiments were performed using continuous operation.

RESULTS

IM for Omron and Pari were similar (20% of nebulizer charge) and greater than the Sidestream (10%). MMADs were similar for all devices but variability was much greater for Omron in the horizontal position. Run time in the tilted position was three times longer when compared to the horizontal (p = 0.02). IM and MMAD were unchanged after Omron robustness testing.

CONCLUSION

Position was an important factor for the mesh device affecting run time and variability in particle distribution. Using a common commercial formulation and continuous operation, drug delivery was similar to an efficient jet nebulizer. The Omron mesh tolerated repeated use with the albuterol formulation.

Assessment methods of inhaled aerosols: technical aspects and applications

The pulmonary route has been used with success for the treatment of both lung (asthma) and systemic diseases (diabetes). The fate of an inhaled drug (absorption and deposition) within human lungs has great importance, particularly in drug development and quality control. This article focuses on the various methods that are now applied for aerosol fate investigation. Several assessment methods, ranging from in vitro assays (impaction and optical systems) to in vivo experiments (imaging and pharmacological methods), are described. In vitro assays measure particle size distribution and emitted drug dose, which could be predictive of lung deposition pattern in vivo. However, in vivo methods provide direct information about the concentration and the location of inhaled drug within lung. Advantages and limitations of the different techniques are identified. In addition to these experimental techniques, mathematical deposition models, elaborated in more realistic conditions and designed to predict the fate of inhaled particles, are also illustrated.