Health Assessment Document for Diesel Emissions - NSCEP | US ...

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direction. For each generation, alveolization is considered to be complete when the number of
alveoli in that generation reaches the number determined by Weibel's model.
C.5.3.3.2. Airway size
Four sets of data are used to determine airway size during postnatal growth: (a) total lung
volume as a function of age; (b) airway size as given by Weibel's model; (c) the growth pattern
of the bronchial airways; and (d) variation in alveolar size with age. From these data, it is found
that the lung volume, LV(t) at age t, normalized to Weibel's model at 4,800 cm 3 for an adult (25
years old), follows the equation
LV(t) = 0.959 x 10 5 (1 - 0.998e -o· 002 t) (em 3 ). (C-63)
The growth patterns of the bronchial airways are determined by the following equations
Dlt) - Diw = ct;[H(t) - H(25)], (C-64)
L;(t) - Liw = PJH(t) - H(25)], (C-65)
11 where Dlt) and Llt) are, respectively, the airway diameter and length at generation i and age t,
12 Diw and Liw the corresponding values for Weibel's model, ai and Pi are coefficients given by
cti = 3.26 x 10- 2 exp[-1.183 (i+1) 0 · 5 ] (C-66)
p. = t.os>