Biomedical Engineering Reference
In-Depth Information
One limitation of pMDIs is that drug deposition in the peripheral airways
is highly dependent on successful coordination between actuation and
inhalation by the patient (Crompton, 1982). For this reason, breath-actuated
pMDIs have been developed. The synchronized delivery of aerosols from the
inhaler with the inhalation performed by patient ensures efficient delivery of
the drug to the deeper regions in the respiratory system (Newman, 2005). An
example of the breath actuated pMDIs is the Autohaler device (Figure 5)
which releases aerosol only when patient inhales when a lever on top of the
device is pulled, resulting in release of aerosol by a vane-spring system
(Newman, 2005). For more knowledge about pMDIs, a review by Newman
(2005) is highly recommended.
(Source: Newman, 2005).
Figure 5. A schematic diagram of the Autohaler pressurized metered dose system
which operates by utilizing a vane-spring system that releases the aerosol when patient
inhales and pulls a lever located at the opposite end of the mouthpiece.
3.2. Dry Powder Inhalers (DPIs)
Dry powder inhalers (DPIs) were first introduced in the 1970s. In contrast
to pMDIs, DPIs are free of propellants and no coordinated inhalation is
required. DPIs usually have micronized drug to facilitate particle penetration
to the peripheral airways on inhalation. However, micronisation may
compromise drug flow properties, necessitating the addition of a flow aid or
