Case Studies in the Human Respiratory System - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 311

main bronchus. The lowest numbers of escaped particles are found in the upper
right bronchus and the upper left bronchus, which is caused by the larger bifurca-
tion angles as well as the G3 L-dorsal angles (Table 8.11 ). Comparisons between
the AA-model and the REC-model show a difference of 2 and 5 % deposition for
5 and 40

m particles
(92-98 %) as expected, but more interesting is the location of deposition. In the
AA-model, deposition is found in the lower trachea region which is not found in the
REC-model.

μ m particles, respectively. High deposition is found for 40 μ

8.5.5 Considerations for Modelling Pulmonary Drug Delivery

Ventilation in the respiratory airway is accomplished by the transport of inspired air
down pressure gradients within the airways. This process involves the alternating
contraction and relaxation of the respiratory muscles which overcome the pressure
drop caused by viscous losses such as shearing forces within the fluid, the friction
between the air and walls of the airways, and the resistance presented by the ir-
regularities of the airways. Under steady laminar flow conditions of 15 L/min, the
required effort by the respiratory muscle to overcome the pressure difference for the
AA-model is nearly twice as high as that required for the REC-model. The primary
cause of greater resistance in the AA-model is the narrowed airways and the occlu-
sion of two of the branches. This suggests that during the period of an acute asthma
episode, the work of breathing for the patient in order to achieve the same tidal
volumes is doubled compared to the recovered state, which can lead to respiratory
muscle fatigue. The walls created within the model are assumed rigid and smooth
whereas in reality the walls may exhibit some roughness and elasticity. The inclu-
sion of these attributes may alter the predicted magnitudes of the pressure drop, but
it is unlikely to alter the comparative ratio between the two pressure drops from the
computational models. Furthermore, to be included, such data need to be accurately
obtained, since approximations may actually cause further errors if the elasticity and
roughness of the airway walls are not well known.
Treatment of asthma is most commonly employed during the onset of the asthma
episode. Particles are atomized into smaller particles through ventilators or other drug
delivery devices and inhaled through the mouth. In this study the particle deposition
patterns showed that the airway geometry had a significant affect. Although the
indentations from the aortic arches of the AA-model and REC-model do not change
significantly, the additional effect of the narrowed airways enhances the impactability
of the particles. Drug particles are delivered with the target being the region of
airway occlusion; however the deposition patterns show that particles travel through
regions where the geometry does not deviate greatly and eventually deposit at the
bifurcations. The results showed that a significant number of particles pass through
the right main bronchus, and therefore deposition of particles will be in the right
lung airways. This is a consequence of the airway branching angle at the carina
bifurcation which produces the left main bronchus at a more obtuse angle than that