Biomedical Engineering Reference
In-Depth Information
the particle flow were discussed. This case study also investigated further the appli-
cation of nasal drug delivery. While the nasal cavity's natural function is to filter out
toxic particles, there is an opportunity to exploit the highly vascularised walls for
drug delivery. Nasal sprays deliver atomized particles into the nasal cavity at high
velocities. The structure of the atomized spray from a nasal spray was presented in
order to identify the parameters that would affect the setting up of the initial parti-
cle boundary conditions for the CFD simulations. Parameters that were important,
among others, included
swirl effects, the spray cone angle, initial particle velocity
and
the insertion angle
which were evaluated for deposition efficiency under high
and low inertial particles.
For a flow rate of 20 L/min 10-20
m, particles were sensitive to initial injection
velocity, insertion angle, and spray cone angle as their size increased. Larger par-
ticles exhibited very high Stokes numbers (inertial parameter) causing them to be
insensitive to these parameters. Current commercially available nasal sprays produce
mean size particles of 45-60
μ
μ
m. This presents a problem because larger particles
(
m) are relatively insensitive towards initial injection conditions and are likely
to deposit in the anterior portion of the nose decreasing the drug delivery's efficiency.
Producing smaller particles (
≥
20
μ
m) during atomization is an option for designers;
however smaller particles are more inclined to follow the airflow and can lead to
deposition beyond the nasal pharynx.
The ideas formulated can be used as a basis for improving the design of nasal
spray devices to achieve better drug delivery, such as (i) redirecting the release point
of the spray (i.e. the insertion angle) to align with flow streamlines, (ii) controlling
the particle size distribution and (iii) controlling the particle's initial velocity. In the
attempt to replicate actual nasal spray applications while isolating the investigating
parameters, idealised injected conditions for the particles were used. Further studies
have been performed (Kimbell et al. 2004, 2007) which also tested some of the
spray characteristics. Interestingly, this field of research can be extended to compare
results with other nasal cavities to include the permeability effects of nasal hairs
and to establish more accurate initial particle conditions such as the instantaneous
velocity at injection that can include swirl effects.
≤
20
μ
8.5
Effects of Asthma on the Fluid-Particle Dynamics
in the Lung Airways
In this case study we move deeper into the respiratory system, to the tracheal-
bronchial airway tree in the lungs. Models of the lung airways are presented along
with some flow features and particle deposition. The case study will focus on a
real application involving the affects of asthma. The physiological characteristics of
asthma include variable airway obstruction and increased airway responsiveness to
stimuli. This causes the passages to narrow, reducing the flow of air in and out of the
lungs. A comparison between two models (one immediately after asthma and another
thirty days later) is undertaken to determine the disparities in the inhalation efforts
and the airway branch diameters caused by physiological changes in the airways.
Search WWH ::
Custom Search