Journal of Applied Physiology, Vol 59, Issue 3 807-813, Copyright © 1985 by American Physiological Society
Effect of hilar nerve denervation on breathing and arterial PCO2 during CO2 inhalation
C. Flynn, H. V. Forster, L. G. Pan and G. E. Bisgard
We determined the effects of denervating the hilar branches (HND) of the
vagus nerves on breathing and arterial PCO2 (PaCO2) in awake ponies during
eupnea and when inspired PCO2 (PICO2) was increased to 14, 28, and 42 Torr.
In five carotid chemoreceptor-intact ponies, breathing frequency (f) was
less, whereas tidal volume (VT), inspiratory time (TI), and ratio of TI to
total cycle time (TT) were greater 2-4 wk after HND than before HND. HND
per se did not significantly affect PaCO2 at any level of PICO2, and the
minute ventilation (VE)-PaCO2 response curve was not significantly altered
by HND. Finally, the attenuation of a thermal tachypnea by elevated PICO2
was not altered by HND. Accordingly, in carotid chemoreceptor-intact
ponies, the only HND effect on breathing was the change in pattern
classically observed with attenuated lung volume feedback. There was no
evidence suggestive of a PCO2-H+ sensory mechanism influencing VE, f, VT,
or PaCO2. In ponies that had the carotid chemoreceptors denervated (CBD) 3
yr earlier, HND also decreased f, increased VT, TI, and TT, but did not
alter the slope of the VE-PaCO2 response curve. However, at all levels of
elevated PICO2, the arterial hypercapnia that had persistently been
attenuated, since CBD was restored to normal by HND. The data suggest that
during CO2 inhalation in CBD ponies a hilar-innervated mechanism influences
PaCO2 by reducing physiological dead space to increase alveolar
ventilation.
