Droplets Produced by Medical Nebulizers: Discussion (Part 2)
As the temperature of the ultrasonic nebulizer solution increases, the extra water needed to saturate the air is likely to come from the dense aerosol cloud within the nebulizer chamber. The output therefore is not likely to change as the nebulizer temperature rises as suggested by the results (Fig 4). The two-way valve situated before the mouthpiece of the ultrasonic nebulizer filters a high proportion of the larger droplets from the aerosol stream. The effect therefore is to reduce the output and mass median aerodynamic diameter of the droplets. This effect depends on the flow rate of the aerosol stream and hence the velocity of the droplets. There is an optimum flow rate, however, due to opposing effects: At the lower flow rate, the droplets tend to settle into the nebulizer solution or within the tubing and the output is reduced. At the higher flow rates, the droplets are more likely to impact within the tubing and on the valve. The optimum flow rate for this system was found to be approximately 20 L/min (Fig 4). birth control pills
Although it is known that the concentration of the solution in the jet nebulizer bowl increases with generation due to the release of vapor in addition to the liquid droplets, the changes in solution concentration in the droplets measured in the experiments reported here are generally much greater. This is because the cold aerosol droplets generated from the jet nebulizer solution will evaporate a substantial amount of water as they rapidly warm up to room temperature. Therefore, the concentration of solute in the droplets increases to a value determined by the difference between the ambient temperature and the temperature of the nebulizer solution and to a lesser extent due to the gradual increase of the concentration in the nebulizer.