Journal of Applied Physiology, Vol 43, Issue 1 20-26, Copyright © 1977 by American Physiological Society
Effects of thoracic dorsal rhizotomies on the respiratory pattern in anesthetized cats
R. Shannon
Experiments were conducted to determine if thoracic wall proprioceptor
afferents are involved in the modulation of respiratory activity during
eupnea. The effects of elimination of thoracic wall afferents (thoracic
dorsal rhizotomies (TDR) on tidal volume (VT), frequency (f), inspiratory
time (ti) and expiratory time (te) were studied in vagotomized cats
anesthetized with diallylbarbituric acid (Dial). Dorsal rhizotomies 1-12
resulted primarily in a decreased VT and ti, and an increased f. Further
experiments were performed to determine if these changes in respiratory
pattern could be correlated with known reflexes from the middle and lower
intercostal muscles, or lungs, via thoracic dorsal roots. Afferents from
these sources were eliminated by TDR 5-9, 10-13, and 1-4. TDR 1-4 had no
significant effect on the respiratory pattern. TDR 5-9 and TDR 10-13
produced changes similar in direction to TDR 1-12. The results indicate
that: a) afferents 1-4 from the upper intercostal muscles and lungs
(sympathetic afferents) do not contribute significantly to the control of
the spontaneous respiratory rhythm, and b) afferents via the middle
thoracic roots, 5-9, and the lower thoracic roots, 10-13, contribute
significantly to the rhythm. The results do not completely correlate with
known intercostal reflexes, but it is suggested that elimination of
intercostal muscle proprioceptor afferents is responsible for the observed
effects of thoracic dorsal rhizotomies.
