Table 1 Comparison of different types of nebulizers

Jet [68]

Pressurized gas forms a jet passing through a tube creating a low-pressure zone (Venturi effect) that draws liquid formulation into the jet stream (Bernoulli effect)

• With a corrugated tube

• Cheap

• Inefficient

• With a collection bag

• Easy to use

• Difficult to clean

Droplet size > 5 μm

• Breath-enhanced jet nebulizers

• Effective in delivering drugs that cannot be delivered with pMDIs and DPIs

• Need compressed gas and additional tubing

• Breath-actuated jet nebulizers

• Breath-enhanced and breath-actuated options

Ultrasonic [70, 131]

Piezoelectric crystal converts an electrical signal into high-frequency vibrations in the liquid, forming an aerosol using cavitation and capillary mechanisms

• Small volume (e.g. for medications)

• Easy to use

• Large residual volume

• Large volume (e.g. for hypertonic saline used for sputum induction)

• More efficient than jet nebulizers

• Unable to nebulize viscous solutions

Drug output alpha vibration amplitude

• Shorter nebulization time (better for large volumes)

• Degradation of heat-sensitive materials—so inappropriate for proteins

Particle size alpha vibration frequency

Droplet size variable, may be less than 5 μm

• Aerosol temperature 10–14 °C higher than that in jet nebulizer

• Large device size

Vibrating mesh [19, 70]

Aerosol is produced by forcing the liquid using the micropumping action through the vibrating mesh containing funnel-shaped holes

• Active (e.g. Aeroneb®; Aerogen, Galway, Ireland)

• Silent operation, portable

• More expensive

Droplet size < 5 μm

• Passive (e.g. Microair NE-U22®; Omron, Bannockburn, IL, USA)

• Short treatment time

• Cleaning can be difficult

• Minimal residual volume

• Drug dose needs to be adjusted in transition from jet nebulizers

• Self-contained power source

• Inability to use to aerosolize viscous liquids

• Optimize particle size for specific drugs

• Inability to aerosolize drugs that crystallize on drying

• More output efficiency than other nebulizers

• Two to three times higher drug deposition compared with jet nebulizers

• Aerosol temperature usually unchanged

• Unchanged osmolality

• Easy to use