Biomedical Engineering Reference
In-Depth Information
The use of air-jet nebulizers can be traced back to the beginning of 20
th
century and the first nebulizer reported was the ―squeeze-bulb nebulizer‖. This
generates aerosols by forcing medication liquid through a small orifice when a
special bulb is squeezed to generate a liquid spray (Muers, 1997; Placke et al.,
2002; Anderson, 2005) (Figure 8). This old technology device generates
droplets that are too large for efficient deposition in the peripheral airways and
therefore the squeeze-bulb device is now obsolete (Muers, 1997).
(Source: Anderson, 2005).
Figure 8. Squeeze-bulb nebulizer developed in 1940s. A plastic-made device is
attached to a bulb that generates aerosols when squeezed.
Modern air-jet nebulizers convert liquids into aerosols by employing
compressed gas forced at high velocity through a narrow ―venturi‖ nozzle.
This creates an area of negative pressure above the liquid which, by ―Bernoulli
effect‖, draws the liquid up a feed tube as fine filaments that collapse into
aerosol droplets because of liquid's surface tension (McCallion et al., 1996a;
O'Callaghan and Barry, 1997). A small proportion of the aerosol, the
―secondary aerosol‖, is released for inhalation whilst the largest proportion,
the ―primary aerosol‖, is too large to escape the baffles of the nebulizer and
hence is recycled within the device to be atomized further into smaller droplets
that are suitable for inhalation (McCallion et al., 1996a; O'Callaghan and
Barry, 1997). Many modern jet nebulizers are designed to be breath-actuated
or breath-enhanced. Pari jet nebulizers are common examples of breath-
