Study of the technological parameters of ultrasonic nebulization

The principle of an ultrasonic nebulizer is based on the vibrations of a pi ezoelectric crystal driven by an alternating electrical field. These period ic vibrations are characterized by their frequency, their amplitude, and th eir intensity, which corresponds to the energy transmitted per surface unit . When the vibration intensity is sufficient, cavitation occurs, and drople ts are generated. Ventilation enables airflow to cross the nebulizer and to expel the aerosol droplets. For a given nebulizer, the vibration frequency of the piezoelectric crystal is fixed, often in the range 1-2.5 MHz. In mo st cases, an adjustment in vibration intensity is possible by modifying vib ration amplitude. The ventilation level is adjustable. The vibrations may b e transmitted through a coupling liquid-commonly water to a nebulizer cup c ontaining the solution to be aerosolized. In this work, we studied the infl uence of the technological parameters of ultrasonic nebulization on nebuliz ation quality. Our study was carried out with a 9% sodium chloride solution and a 2% protein solution (alpha1 protease inhibitor). Three different ult rasonic nebulizers were used. An increase in vibration frequency decreased the size of droplets emitted. The coupling liquid absorbed the energy produ ced by the ultrasonic vibrations and canceled out any heating of the soluti on, which is particularly interesting for thermosensitive drugs. An increas e in vibration intensity did not modify the size of droplets emitted, but d ecreased nebulization time and raised the quantity of protein nebulized, th us improving performance. On the other hand, an increase in ventilation inc reased the size of emitted droplets and decreased nebulization time and the quantity of protein nebulized because more drug was lost on the walls of t he nebulizer. High intensity associated with low ventilation favors drug de livery deep into the lungs.