Novartis Pharmaceuticals Corporation, San Carlos, California 94577, USA.
J Aerosol Med Pulm Drug Deliv. 2010 Oct;23(5):295-302. doi: 10.1089/jamp.2009.0805.
Droplet evaporation has been known to bias cascade impactor measurement of aerosols generated by jet nebulizers. Previous work suggests that vibrating mesh nebulizers behave differently from jet nebulizers. Unlike jet nebulizers, vibrating mesh nebulizers do not rely on compressed air to generate droplets. However, entrained air is still required to transport the generated droplets through the cascade impactor during measurement. The mixing of the droplet and entrained air streams, and heat and mass transfer occurring downstream determines the final aerosol size distribution actually measured by the cascade impactor. This study is aimed at quantifying the effect of these factors on droplet size measurements for the case of vibrating mesh nebulizers.
A simple droplet evaporation model has been applied to investigate aerodynamic size measurement of drug aerosol droplets produced by a proprietary vibrating mesh nebulizer. The droplet size measurement system used in this study is the Next Generation Impactor (NGI) cascade impactor. Comparison of modeling results with experiment indicates that droplet evaporation remains a significant effect when sizing aerosol generated by a vibrating mesh nebulizer.
Results from the droplet evaporation model shows that the mass median aerodynamic diameter (MMAD) measured by the NGI is strongly influenced not only by the initial droplet size, but also by factors such as the temperature and humidity of entrained air, the nebulizer output rate, and the entrained air flow rate. The modeling and experimental results indicate that the influence of these variables on size measurements may be reduced significantly by refrigerating the impactor down to 5°C prior to measurement. The same data also support the conclusion that for the case of nebulized drug solutions, laser diffraction spectrometry provides a meaningful droplet sizing approach, that is simpler and less susceptible to such droplet evaporation artifacts.
众所周知，液滴蒸发会影响级联撞击器对射流雾化器产生的气溶胶的测量结果。先前的工作表明，振动网式雾化器的行为与射流雾化器不同。与射流雾化器不同，振动网式雾化器不依赖压缩空气来产生液滴。然而，在测量过程中仍需要夹带空气将生成的液滴输送通过级联撞击器。液滴和夹带空气流的混合以及下游发生的热和质量传递决定了级联撞击器实际测量的最终气溶胶粒度分布。本研究旨在量化这些因素对振动网式雾化器情况下液滴尺寸测量的影响。
已应用简单的液滴蒸发模型来研究由专有的振动网式雾化器产生的药物气溶胶液滴的空气动力学尺寸测量。本研究中使用的液滴尺寸测量系统是下一代撞击器（NGI）级联撞击器。模型结果与实验的比较表明，当对振动网式雾化器产生的气溶胶进行尺寸测量时，液滴蒸发仍然是一个重要的影响因素。
液滴蒸发模型的结果表明，NGI 测量的质量中值空气动力学直径（MMAD）不仅受初始液滴尺寸的影响，还受夹带空气的温度和湿度、雾化器输出率以及夹带空气流量等因素的影响。建模和实验结果表明，通过在测量前将撞击器冷却至 5°C 左右，可以大大降低这些变量对尺寸测量的影响。相同的数据还支持这样的结论，即对于雾化药物溶液的情况，激光衍射光谱法提供了一种有意义的液滴尺寸测量方法，该方法更简单，并且不易受到这种液滴蒸发伪影的影响。
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