Mechanisms of Particle Deposition - Aerosols: Measurement, Dosimetry, and Health Effects - page 65

3.7.2.1.2 Turbulent Conditions
Under turbulent low conditions, interception of ibers in the lung may be expressed as 132

⎛ ⎞

2

2 1

4

L L

r

( ) =

f f

2 2 − 1

P Int r − + r a sin (3.40)

⎜ ⎟ a

2

π r 16 4

⎝ ⎠

a a

Asgharian and Yu 133 developed a more complex set of equations to characterize deposition of large
ibers by interception. They found that their equations agreed with the results of Harris and Fraser
(at all aspect ratios and iber sizes tested) in airways from the trachea to the 15th airway generation.
However, they suggested that beyond the 15th generation, their equations are required to adequately
quantify interception, while recognizing that the equations formulated by Harris and Fraser may
still be valid for small ibers having L f / d f ≤ 10 and d f < 1 μm.
Interception can be an important deposition mechanism, particularly for ibers. However, its
signiicance is often underemphasized. The link between the inhalation of asbestos ibers and lung
disease has been well established. 138,139 Martonen and Schroeter 140 have described how the mecha-
nism of interception, and its function in iber deposition in the human lung, may play a signiicant
role in respiratory health and disease.
Due to their high-deposition and low-clearance rates (which will be discussed in detail in
Chapter V), hollow ibers (microtubules) may be an effective and eficient vehicle for the delivery
of inhaled pharmacological drugs. Techniques to generate liposomes as microtubules have been
reported by Johnson et al. 141 The hollow ibers may be illed with pharmaceuticals of choice, and
serve to transport the airborne drugs. The aerodynamic size of a particle may be estimated as 10,142

0.116

⎛
⎜

⎞
⎟

L
d

f

d = 2.19 d (3.41)

ae f

f

We note that the d ae of a iber is relatively independent of length; therefore, the microtubule can be
packed with a large quantity of drugs without adversely affecting its aerodynamic properties.
Equations have been developed for the aerodynamic properties and behavior of tumbling
ibers. 142,143 The integration of these formulae into the aerosol delivery program 75 will produce an
inhalation therapy model for the administration of aerosolized liposomes as microtubules.

3.7.2.2 Electrostatic Charge
When, during aerosol generation, a friction or shear force is applied to the substance to be aerosol-
ized, an electrostatic charge is often imparted to the particles. 3,144,145 In addition, aerosol particles
may pick up charges as a result of collisions with atmospheric aerosols. These electrostatic charges
will affect how particles, especially ultraine particles, are deposited within human lungs. 146
Two types of charging are important for particle deposition in the human lung: image charge and
space charge. Image charge occurs when a charge-carrying particle induces the opposite charge in
an airway surface, thus creating an attraction of the particle to the surface. Image charge occurs
most often with highly charged particles. Space charge occurs when two particles of the same
charge simultaneously repel, resulting in a particle colliding with the airway wall. Space charge
occurs most often with high concentration, unipolar charged aerosols. 4 A number of studies have
dealt with the various aspects of electric force effects. 147-154
Experimental studies in human airway casts have been used to investigate how charge affects
the deposition of particles in the tracheobronchial tree. Chan et al. 147 found that highly charged
particles, between 2 and 7 μm in size, deposited signiicantly more than uncharged particles of the
same size. Cohen et al. 148 found that charged ultraine aerosols deposit at least three times more