Modeling Deposition of Inhaled Particles - Aerosols: Measurement, Dosimetry, and Health Effects - page 97

impaction. However, particulate matter removal in the nasal passages (and thus total deposition dur-
ing nasal breathing) is highly dependent on particle size and inhalatory volume and low, 118,120,121,123
as well as nasal passage morphology and development. 119,124,125

5.4.4.2 Breathing Pattern
Breathing pattern is an important factor in the respiratory deposition of therapeutic particles, as it
may affect treatment eficiency. 126 Both spontaneous and regulated breathing patterns (Figure 5.8)
have been used in human inhalation studies of particle deposition and clearance. The type of breath-
ing pattern will affect the amount and pattern of particle deposition in the human lung. Studies
comparing deposition data for spontaneous breathing patterns have been performed. 19,126-129
Breathing pattern is typically described in terms of tidal volume (volume of air inhaled) and
low rate. In general, larger tidal volumes result in higher particle deposition in the human lung
as particle-laden air penetrates deeper into the lung. Lower low rates also result in higher particle
deposition in the peripheral lung as velocities are slower and particles have more time to deposit by
sedimentation or diffusion (see Chapter 6 for discussion on deposition mechanisms).

5.4.4.2.1 Spontaneous Breathing
Spontaneous breathing is unprescribed, with subjects breathing at their own pace, with only approx-
imate tidal volume or low requirements. Figure 5.8A illustrates the relationship between tidal vol-
ume and time for a typical spontaneous breathing pattern. Chan and Lippmann 26 and Brown et al. 130
have used spontaneous breathing patterns in the study of deposition of inhaled particles. Other stud-
ies have shown that spontaneous breathing of human subjects resulted in large intersubject variabil-
ity in the fractional deposition of inhaled particles. 127,131,132 Furthermore, Bennett and Smaldone 128
determined that it was differences in spontaneous breathing pattern (and not peripheral air space
size or morphology) that inluenced intersubject variation in peripheral deposition.

5.4.4.2.2 Regulated Breathing
Regulated or academic breathing occurs when human subjects are required to follow a speci-
ied breathing pattern that varies from their own natural breathing rate. In this pattern, illus-
trated in Figure 5.8B, a constant low rate is maintained. Regulated breathing has been used to
attempt to mitigate the intersubject variability introduced by spontaneous breathing. 128 Studies

Average tidal volume

1

0 4 8 12 16

Times (s)

20 24 28 32

(A)

Tidal volume

1

0 4 8 12 16

Times (s)

20 24 28 32

(B)

FIGURE 5.8 Spontaneous (A) and controlled (B) breathing patterns. Note that in spontaneous breathing,
rate and tidal volume may vary, while these are constant in controlled breathing.