Journal of Applied Physiology, Vol 52, Issue 6 1426-1431, Copyright © 1982 by American Physiological Society
Propranolol-vagal-alveolar CO2 interactions on collateral gas flow in dog lungs
L. E. Olson and N. E. Robinson
The mechanical properties of a collaterally ventilating lung segment were
studied in 18 anesthetized paralyzed mongrel dogs artificially ventilated
with room air end-tidal CO2 fraction = 5%. Nine dogs were pretreated with
propranolol, and nine dogs were not. With 0, 5, or 12% CO2 in O2 flowing
into the segment, steady-state resistance of segmental airways (Rss) and
time for 90% pressure equilibration (T90) between the segment and airway
opening after flow was discontinued were determined at functional residual
capacity with the vagus nerve ipsilateral to the segment intact, sectioned,
or electrically stimulated. Vagal stimulation increased Rss and T90 at all
CO2 levels, whereas unilateral vagotomy had no effect. Propranolol
treatment enhanced the increase in Rss caused by vagal stimulation at low
but not at high CO2 levels, suggesting that high CO2 mimics the effect of
propranolol on Rss. High levels of CO2 did not have the same effect as
propranolol on T90, propranolol treatment reducing the increase in T90
caused by vagal stimulation at high but not at low CO2 levels. These
results demonstrate that local changes in alveolar CO2 tensions modify but
do not abolish the effect of vagal stimulation on collateral ventilation.
