EFFECT OF TIDAL VOLUME ON THE OUTPUT AND PARTICLE-SIZE DISTRIBUTION OF HYPERTONIC SALINE FROM AN ULTRASONIC NEBULIZER

The purpose of the present study was to measure the output and particl e size distribution of hypertonic saline from an ultrasonic nebulizer over the range of tidal volumes (VT) used in an epidemiological survey of asthma in children. A Starling pump was used to generate different VTS from 250 to 500 ml, at different respiratory rates of 12 and 20 b reaths min(-1), to cover the normal range of respiratory pattern of ch ildren aged 7-14 yrs. The Starling pump was connected to a Timeter Com puneb Ultrasonic Nebulizer Model MP 500 with 24 cm of corrugated aeros ol tubing, ID 2.2 cm, and a two-way non-rebreathing valve. Nebulizer o utput was measured by weighing the nebulizer chamber plus tubing and v alve before and after each nebulization. To measure particle size dist ribution, a Malvern Particle Sizer M 3.0 (laser diffraction) was used, with a special adapter attached between valve and Starling pump. Nebu lizer output increased linearly from 1.6 to 2.5 ml.min(-1) for VT 250 to 500 ml, with Little influence by the respiratory frequency. Further more, we found that in the range of VT=3DO-500 ml the mass median aero dynamic diameter (MMAD) was 2.61 mu m, with 100% of the particles less than 5 mu m, whereas at VT=150-250 ml the MMAD was 8.89 mu m, with 90 % larger than 5 mu m. As output from this ultrasonic nebulizer correla tes linearly with tidal volumes, size correction may not be necessary in hypertonic saline challenge tests in children. Above a VT of 300 ml , the MMAD is in the respirable range, with 100% of particles less tha n 5 mu m. However, in children with a VT less than 250 ml, this equipm ent may be unsuitable to perform hypertonic saline challenge tests.