Journal of Applied Physiology, Vol 51, Issue 3 598-606, Copyright © 1981 by American Physiological Society
Flow partitioning in symmetric cascades of branches
B. Snyder, D. R. Dantzker and M. J. Jaeger
We have found markedly nonuniform partitioning of flow in idealized models
of physiological cascades of branches. Liquids having viscosities of
0.8-7.0 cP were used to investigate this effect systematically in a regime
characterizing a limited range of pulmonary flows, comprising inlet flow
rates of 500-3,000 ml/min and branch diameters of 1.0 cm ID. Factors that
affect the nonuniformity of inspiratory flow include inlet velocity profile
and flow rate, cascade aspect (L/D) ratio, exit pressure distribution, and,
to a lesser extent, kinematic viscosity (mu/rho). More qualitative
observations using sinusoidally oscillating airflow revealed inspiratory
and expiratory flow patterns to be quite dissimilar, emphasizing the
inadequacy of a resistance model of flow partitioning based on Kirchhoff's
law. These results might suggest, in part, why regional ventilation in man
is flow or frequency dependent and how bronchial smooth muscle could fine
tune regional ventilation.
