Biomedical Engineering Reference
In-Depth Information
aerosol) are released for inhalation. Ultrasonic nebulizers may incorporate a
fan with variable speed to aid the release of aerosols at the required rate.
Ultrasonic nebulizers vary greatly in design, performance, and features
such as device portability including size and weight. Unlike early ultrasonic
devices which required a main electricity supply, portability has been greatly
enhanced in recent years by manufacturing hand-held battery-powered
devices. However, most ultrasonic nebulizers produce aerosol droplets of high
polydispersity and hence a considerable fraction of the generated aerosols may
not be suitable for deposition in the deep lung. Moreover, unlike jet-
nebulizers, ultrasonic nebulizers are generally inefficient in delivering
suspensions (McCallion et al., 1996b), highly viscous solutions (McCallion
and Patel, 1996) and liposomes (Elhissi and Taylor, 2005). Furthermore,
ultrasonic energy may generate heat and markedly increase the temperature of
the fluid during nebulization (Taylor and Hoare, 1993), resulting in the
degradation of labile substances such as proteins (Niven et al., 1995) or some
antibiotics in solution (Dennis and Hendrick, 1992). Nowadays, ultrasonic
nebulizers are being replaced by the recently commercialized vibrating-mesh
nebulizers.
(Source: O'Callaghan and Barry, 1997).
Figure 10. Schematic diagram of an ultrasonic nebulizer showing the generation of
aerosols from the apex of the fluid with a piezoelectric crystal vibrating underneath.
