Particle removal by the respiratory system note on the removal of airborne particulates by the human respiratory tract with particular reference to the role of diffusion

Abstract

Calculations of the contribution of diffusion to lung retention given previously (W. Findeisen,Pflüg. Arch. f. d. ges. Physiol.,236, 367–379, 1935; H. D. Landahl,Bull. Math. Biophysics,12, 43–56, 1950) contained an error appreciably underestimating the role of diffusion for particles less than a few microns in diameter. In the calculations (Landahl, 1950), a schematic representation of the lungs was modified to conform to the actual resting lung volume by increasing the number of alveolar sacs. A recalculation of total deposition with this chematic model gives too large a retention for very small particles. Hence it seemed appropriate to recalculate the retention for various paricle sizes in various regions of the respiratory tract for several respiratory paterns, using the original schematic model but assuming that the estimates reflect conditions in a deflated lung. For a given tidal air the sizes of the alveolar ducts and sacs were assumed to expand so that the total volume of the model was equal to 2.5 liters plus one half of the tidal air, i.e., the mean lung volume. The results of these calculations are appreciably different from those given previously, but the differences are serious only for particles of about 0.1 micron or less. Also given is an approximation method for calculating the probability of impaction of droplets against nasal hairs.