Estimation of fibrous aerosol deposition in upper bronchi based on experimental data with model bifurcation.

Abstract

Lung deposition of fibrous aerosol was studied by using a model of the lung bifurcation with dimensions based on the symmetric model A of Weibel. The fibrous aerosols were introduced to the model under steady inspiratory flow conditions. Glass fibers depositing in the daughter tubes and these escaping from them were observed under a scanning electron microscope (SEM). The deposited fractions were calculated for each length and diameter using a bivariate lognormal distribution. In this study the authors propose empirical equations to estimate total deposited fractions of fibrous aerosol at upper bronchi. The dimensionless relationship among deposited fractions Fd, Stokes number St for randomly-oriented fibers and interception parameter I were used to estimate the deposited fraction at arbitrary position in the upper bronchi. The calculation procedure for Fd(St,I) consists of two steps: the determination of the four deposited fractions, Fdn for each In (n=1-4) followed by interpolation or extrapolation from Fdn to find the deposited fraction Fd at a given I. With this procedure, it is possible to determine the deposited fraction Fd in the range of 2 x 10(-3)<St<5 x 10(-2) and 5 x 10(-4)<I<5 x 10(-2). Penetration from the trachea to the 10th generation of lung bifurcation was calculated for several cases of fiber diameter, length and flow rate. In the case corresponding to an inspiration of 500 cm3 air at a constant rate for 2 s, more than half of the fibers with a length of 100 microm and diameter of 3 microm are deposited at upper bronchi but more than 90% of fibers of the same length and 1 microm in diameter pass through the region.