Journal of Applied Physiology, Vol 68, Issue 5 2150-2158, Copyright © 1990 by American Physiological Society
Responses of single phrenic motoneurons to altered ventilatory drives in anesthetized dogs
B. P. Lee, J. Green and S. T. Chiang
Department of Physiology, National Yang-Ming Medical College, Taiwan, Republic of China.
We studied the effects of altered ventilatory drives on the activity of the
whole phrenic nerve and single phrenic motoneurons in dogs anesthetized
with alpha-chloralose and paralyzed with gallamine triethiodide. Single
phrenic motoneurons were classified as either late-onset or early-onset
motoneurons (LOM and EOM, respectively), depending on the time of onset of
their activity during inspiration. Increase in ventilatory drive was
induced by altering chemical drive with changes in arterial blood gases and
also by altering the vagal afferent contribution to ventilatory drive. The
latter was accomplished by inducing pulmonary gas embolism (PGE) during
hyperoxia. Whole phrenic nerve activity was increased by both types of
increase in ventilatory drive. In both cases, changes in the firing pattern
of LOMs and EOMs were responsible for the increased phrenic output. The
changes in post-PGE firing pattern of the LOMs generally consisted of a
shift in the time of onset to an earlier point in inspiration and an
increase in the number of spikes per inspiratory cycle. Vagotomy abolished
the difference between the contributions of LOMs and EOMs to the phrenic
response to PGE. Data from dogs studied while they were breathing
spontaneously were qualitatively the same as those from the paralyzed
animals, indicating no major role for phasic volume feedback in these
responses. Our data regarding altered chemical drive are similar to those
reported earlier in other species, whereas those regarding PGE demonstrate
that vagally mediated increases in ventilatory drive affect both LOMs and
EOMs, although LOMs are affected to a greater degree.(ABSTRACT TRUNCATED AT
250 WORDS)
