Journal of Applied Physiology, Vol 59, Issue 6 1757-1765, Copyright © 1985 by American Physiological Society
Effect of transpulmonary and driving pressures on collateral gas flow in dog lungs
L. E. Olson
The effect of changing segment pressure (Ps) and airway opening pressure
(Pao) on flow through a collaterally ventilating lung segment was evaluated
in intact and excised dog lungs. He, N2, and SF6 were passed through the
lung segment distal to a catheter wedged in a peripheral airway at driving
pressures (Ps - Pao) between 0.25 and 2 cm H2O. Eight excised caudal lobes
were studied at Pao = 5, 10, and 15 cm H2O. Flow was directly related to Ps
- Pao and Pao and inversely related to the density of the gas. A
dimensionless plot of the driving pressure normalized to a reference
dynamic pressure as a function of Reynolds number (Re) indicated that flow
through the segment behaved as if it were laminar at Re less than 100 and
that increasing Pao increased the dimension of the pathways conducting flow
as shown previously. Small changes in Ps had no effect on pathway geometry
or on the pattern of flow through the segment at Pao = 10 and 15 cmH2O. At
Pao = 5 cm H2O increasing segment pressure appeared to increase the
dimensions of the flow pathways slightly. Similar changes in Ps - Pao had
no consistent effect on flow pattern or pathway geometry in six
anesthetized, paralyzed, vagotomized dogs at functional residual capacity
or after widely opening the chest (Pao = 5 cm H2O). These results suggest
that, at large lobe volumes, airways (including collateral pathways) are
maximally dilated and therefore relatively insensitive to small changes in
segment pressure.(ABSTRACT TRUNCATED AT 250 WORDS)
