Journal of Applied Physiology, Vol 48, Issue 2 302-307, Copyright © 1980 by American Physiological Society
Characteristics of sustained graded inspiratory inhibition by phasic lung volume changes
J. P. Baker Jr and J. E. Remmers
The dynamic characteristics of graded reversible inspiratory inhibition by
vagal feedback were investigated in pentobarbital-anesthetized paralyzed
cats, ventilated with a servo respirator. The volume and time associated
with various levels of graded inhibition were determined by using a series
of constant-flow lung inflations. Protracted phrenic inhibition was
produced by lung inflation, which was arrested when the phrenic discharge
was partially inhibited. Thereafter, the volume was withdrawn along a
trajectory that approximately paralleled the fall in inhibitory threshold.
This volume-withdrawal trajectory would be expected to produce a sustained
nearly constant level of inhibition based on the results determined from
the constant-flow inflations. However, the observed inhibition exceeded
that expected, increasing to a maximum and then decreasing to expected
values over a period ranging from 1 to 2 s in most animals. This excess
inhibition cannot be attributed to the known dynamic properties of
pulmonary stretch receptors; their activity should be reduced, for any
particular lung volume, during the volume withdrawal maneuver. These
results suggest a central integrative processing of vagal afferent activity
that causes inhibition to lag volume. This delay acts to promote
inspiratory off-switching because it prevents the development of a
protracted period of reversible inhibition.
