Journal of Applied Physiology, Vol 64, Issue 6 2614-2621, Copyright © 1988 by American Physiological Society
Axial dispersion in respiratory bronchioles and alveolar ducts
W. J. Federspiel and J. J. Fredberg
Department of Pediatrics, Harvard University, Boston, Massachusetts 02215.
The mixing of gases in the pulmonary acinus was characterized by analyzing
axial gas dispersion during steady flow in models of respiratory
bronchioles and alveolar ducts. An analysis (method of moments) developed
for addressing dispersion in porous media was used to derive an integral
expression for the axial dispersion coefficient (D*). Evaluation of D*
required solving the Navier-Stokes equations for the flow field and a
convection-diffusion type equation arising from the analysis. D* was
strongly dependent on alveolar volume per central duct volume, the aperture
size through which the alveoli communicate with the central duct, and the
Peclet number (Pe). At smaller Pe (flow rate) D* was substantially smaller
than the molecular diffusion coefficient, whereas at larger Pe (flow rate)
D* was much greater than the Taylor-Aris result for flow-enhanced
dispersion in straight tubes. Also, flow-enhanced dispersion became
appreciable at smaller Pe than indicated by the Taylor-Aris result. These
behaviors transcend both the lower and upper limits established previously
for gas mixing in the pulmonary acinus.
