Highfrequency source

Figure 2 Schematic of an ultrasonic nebulizer.

Therapeutic mist

Solution

Pressurized gas

Area of negative

Baffle

Figure 3 Schematic of an air-jet nebulizer.

the device chamber, of a precise frequency that generates an aerosol cloud at the solution surface.

The aerosol produced by an air-jet nebulizer (Fig. 3) is generated by a completely different principle. When compressed air is forced through an orifice, an area of low pressure is formed where the air jet exists. A liquid may be withdrawn from a perpendicular nozzle (the Bernoulli effect) to mix with the air jet to form droplets. A baffle (or baffles) within the nebulizer is often used to facilitate the formation of the aerosol cloud. Carrier air (oxygen) can be used to generate the "air jet." Alternatively, compressors may be used to generate the airstream.

The nebulized aerosol may be administered during a normal breathing pattern via a mouthpiece, inserted into a ventilation circuit or via a tracheostomy. Alternatively, a ventilation mask can be used. Air-jet nebulizers are far less convenient than ultrasonic nebulizers, which is the principle advantage of the latter. Although major improvements have been made using microelectronics to minimize and produce handheld nebulizers, and a number of specialized companies are known to be working on developing portable liquid-based delivery devices (e.g., Aerogen, Aradigm, BattlePharma) [19-22], these systems are still not widely commercially available. Furthermore it is believed that such systems will still be less portable than the MDI or contemporary DPI devices.

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