Journal of Applied Physiology, Vol 68, Issue 1 76-83, Copyright © 1990 by American Physiological Society
Diffusivity dependence of multiple-breath washouts of lung periphery
G. G. Berdine, D. Dale, J. E. Johnson and J. L. Lehr
Department of Medicine, University of Texas Health Sciences Center, Audie L. Murphy Memorial Veterans Hospital, San Antonio 78284.
Subpleural concentrations of He and SF6 were measured during
multiple-breath washouts from isolated dog lungs. Tidal volume, inspiratory
flow, and frequency were in the normal range of canine ventilation. For
each gas, there was a local minimum in concentration during inspiration
(Cinsp) and a local maximum in concentration during exhalation (Cexp). SF6
exhibited a deeper inspiratory trough than He for each breath of every
washout. For large tidal volumes (10-20 ml/kg), Cexp approximated a single
exponential decay and He was cleared more rapidly than SF6. For small tidal
volumes (2.5 ml/kg), Cexp was multiexponential and SF6 was cleared more
rapidly than He. Cinsp/Cexp (a measure of the depth of the inspiratory
trough) and the kinetics of Cexp decay were determined for washouts using a
tidal volume of 10 and 20 ml/kg and different inspiratory flows. Under all
conditions, an increase of inspiratory flow resulted in a deeper
inspiratory trough for both He and SF6. For washouts using 10 ml/kg and 60
breaths/min, an increase of inspiratory flow increased the clearance of
both gases. In washouts using lower ventilatory frequencies, gas clearance
was independent of inspiratory flow. These findings are contrary to
predictions of contemporary models of convection and diffusion in the lung.
This study suggests that convective axial mixing and radial diffusion in
the airways are important determinants of pulmonary gas transport.
