Chest
Volume 97, Issue 6, June 1990, Pages 1327-1332
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Droplets Produced by Medical Nebulizers: Some Factors Affecting Their Size and Solute Concentration

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The effect of nebulizer solution temperature and dilution air humidity on the size and solute concentration of aqueous aerosol droplets were studied. Four combinations of jet-nebulizers with air compressors or oxygen sources and one ultrasonic nebulizer were tested. The temperature to which the nebulizer solution of each system fell during generation was measured. The nebulizers were then kept at set temperatures, generated aerosols collected and either droplet size or solute concentration measured. The droplet solute concentration was found to increase. The droplet size decreased along with the droplet solute concentration increase. The ultrasonic nebulizer also was tested: its high output made the concentration of the solution in the droplets much more stable. However, the proportion of droplets depositing in the tubing and valves changed markedly with aerosol flow rate. The potential for large changes in droplet solute concentration, droplet size and output during nebulization should be considered in therapeutic and diagnostic applications of nebulized aerosols.

Section snippets

METHODS

The following products were assessed: Cadema nebulizer (Cadema Medical Products Inc., Middletown, NY) with compressed oxygen at 8 L/min; Up-Draft nebulizer (Hudson Up-Draft Oxygen Therapy Sales Co., Temecula, CA) with compressed oxygen at 8 L/ min: Up-Draft with Flatus Mk.V air compressor (Mavmed, Anaesthetic Supplies Pty. Ltd, Sydney, Australia)—this system is equivalent to Tote-A-Neb, Hospitak Inc., Lindenhurst, NY (private communication, Laura Martinazzi); Up-Draft with Aerosol-One air

RESULTS

The fall in temperature with time of nebulization for each of the nebulizer-generator systems is shown in Figure 1. For the jet nebulizers, the temperature falls to a steady value Ts which is 5 to 6°C below the ambient temperature at the lower flow rates of the air compressors, and 11 to 15°C at 8 L/min flow rate from a gas cylinder. Most of this temperature change occurs in the first 4 min of aerosol generation. By contrast, the ultrasonic nebulizer increases in temperature by approximately

DISCUSSION

The fact that the nebulizer solution temperature of jet nebulizers falls during generation has been well documented. The heat loss is due to the evaporation of the nebulizer solution to saturate the gas used to generate the aerosol and some cooling due to adiabatic expansion of the generating gas.14, 18 This evaporation also leads to an increase in solute concentration of the nebulizer solution.18 The gas from a compressed gas cylinder contains no water vapor, while an air compressor supplies

ACKNOWLEDGEMENT

The authors would like to thank Mr. Ian Spiers for the preliminary data on the Mist-O2-Gen ultrasonic nebulizer, colleagues in the Departments of Thoracic and Nuclear Medicine at the Royal Prince Alfred Hospital Camperdown for assistance and encouragement, and the Asthma Foundation of New South Wales for financial support.

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    Manuscript received July 18; revision accepted December 1.

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