Gatnash A A, Chandler S T, Connolly C K
Dept of Medicine, Memorial Hospital, Darlington, UK.
Eur Respir J. 1998 Aug;12(2):467-71. doi: 10.1183/09031936.98.12020467.
Reproducibility and comparability of bronchial challenge tests depends critically on accurate assessment of nebulizer output. Evaporation during nebulization means that simple weighing is inaccurate, overestimating the delivered dose of active ingredient. We wanted to quantify this effect in the context of intermittent nebulization, using a dosimeter as used in bronchial provocation tests. Output of three types of nebulizer, from the MEFAR dosimeter, was measured by radioactive tracer, using a standard solution of technetium-99m-pertechnetate (1.5 kBq x mL(-1)) in 4 mL of normal saline. The aerosol was impacted by suction onto a microfilter, and the radioactivity measured. Nebulizers were weighed before and after nebulization. Ratio of nebulized volume calculated from the radioactivity on the filter, to the total volume loss by weight, was expressed as nebulized ratio. The effect on output of two concentrations of methacholine, two tracers of different weights, and change in temperature, were assessed. Nebulized ratio varied between 44.1-71.6%. Results were more consistent within the same type of nebulizer than between different makes. Neither changes in molar concentration nor molecular weight affected nebulizer output or nebulized ratio. Mean nebulized ratio was 58.5%, showing that calibration by weighing, overestimates the delivered dose by a factor of approximately two. Measuring radioactivity eluted from a microfilter, onto which nebulized output had been impacted proved to be a satisfactory method of calibration.
支气管激发试验的可重复性和可比性关键取决于雾化器输出量的准确评估。雾化过程中的蒸发意味着简单称重并不准确，会高估活性成分的输送剂量。我们希望在间歇性雾化的背景下，使用支气管激发试验中使用的剂量计来量化这种影响。使用99m锝-高锝酸盐（1.5 kBq×mL⁻¹）的标准溶液在4 mL生理盐水中，通过放射性示踪剂测量了MEFAR剂量计中三种类型雾化器的输出。通过抽吸将气溶胶冲击到微滤器上，并测量放射性。雾化前后对雾化器进行称重。根据滤器上的放射性计算出的雾化体积与重量损失的总体积之比表示为雾化比。评估了两种浓度的乙酰甲胆碱、两种不同重量的示踪剂以及温度变化对输出的影响。雾化比在44.1%至71.6%之间变化。同一类型雾化器内的结果比不同品牌之间的结果更一致。摩尔浓度和分子量的变化均未影响雾化器输出或雾化比。平均雾化比为58.5%，表明通过称重进行校准会高估输送剂量约两倍。测量从微滤器上洗脱的放射性，雾化输出已冲击到该微滤器上，这被证明是一种令人满意的校准方法。
