Biomedical Engineering Reference
In-Depth Information
enhanced devices which operate by employing vent systems that close during
exhalation (Figure 9).
Air-jet nebulizers are well established in aerosol delivery of a wide variety
of formulations with different properties. This includes delivery of novel
formulations such as liposomes (Taylor et al., 1989; Elhissi and Taylor, 2005).
A disadvantage of air-jet devices is the decrease in temperature of the fluid (by
10-15 ºC) caused by solvent evaporation during nebulization (Clay et al.,
1983; Taylor et al., 1992), which may induce bronchoconstriction in asthmatic
patients (Lewis, 1983). In spite of that, jet nebulizers remain the most
commonly used nebulizers since they are relatively cheap, easy to use and are
capable of producing small aerosol droplets for deep lung deposition.
(Source: O'Callaghan and Barry, 1997).
Figure 9. Design of a modern air-jet nebulizer. This shows how the vent system works
during inhalation (left) and exhalation (right).
3.3.2. Ultrasonic Nebulizers
Ultrasonic nebulizers were introduced in the 1960s for humidification
applications in respiratory care units (Tovell and D'Ambruoso, 1962).
Ultrasonic nebulizers rely on a piezoelectric crystal transducer that vibrates at
a high frequency (between 1-3 MHz) to convert liquid into aerosol droplets
(Taylor and McCallion, 2002) (Figure 10). As for air-jet nebulizers, large
droplets are recycled by the nebulizer baffles whilst smaller ones (secondary
