Journal of Applied Physiology, Vol 60, Issue 2 479-485, Copyright © 1986 by American Physiological Society
Role of vagal and spinal sensory pathways on eupneic diaphragmatic activity
Y. Jammes, M. J. Mathiot, S. Delpierre and C. Grimaud
The interactions between vagal and spinal afferents in the control of
eupneic diaphragmatic activity were studied in two groups of cats
anesthetized either with pentobarbital sodium (SPB) or with ethyl
carbamate-alpha-chloralose (ECC), which enhanced spinal reflexes. Under
both conditions of anesthesia two experimental protocols were performed: 1)
bilateral cervical vagotomy followed by spinal section at C8 level or 2)
spinal section followed by vagotomy. Changes in integrated diaphragmatic
activity (Edi) were studied during eupneic ventilation and tracheal
occlusion at end expiration. Vagotomy always significantly increased the
amplitude of Edi during eupnea (SPB + 30%; ECC + 15%) and prolonged its
duration (Tdi) (SPB + 110%; ECC + 75%) but did not modify the overall shape
of the Edi vs. time relationship. Spinal section induced reverse changes in
the amplitude of Edi, whether vagal afferents were present or suppressed
and modified the shape of the Edi wave, but did not significantly modify
Tdi. These results indicate that both vagal and spinal afferents may
participate in the control of eupneic inspiration but exert different and
interdependent influences on the recruitment and firing time of phrenic
motoneurons. In addition, Tdi measured during tracheal occlusion (Todi) was
markedly prolonged under ECC anesthesia. In this situation spinal section
reduced Todi, which became close to the values obtained in intact or spinal
cats under SPB anesthesia. Thus the response to tracheal occlusion at end
expiration cannot be interpreted as resulting from the sole suppression of
volume related vagal information.
