Journal of Applied Physiology, Vol 53, Issue 1 212-217, Copyright © 1982 by American Physiological Society
Brain hypoxia and control of breathing: role of the vagi
R. W. Chapman, T. V. Santiago and N. H. Edelman
Vagally mediated reflexes play an important role in the generation of
respiratory responses to various stimuli. This study examined the role of
vagally mediated mechanisms in the generation of the respiratory responses
to progressive brain hypoxia secondary to carboxyhemoglobinemia (HbCO
0-55%) in six unanesthetized goats. Ventilation, respiratory cycle timing,
and the lung inflation reflex were measured before and during CO inhalation
in intact and bilaterally vagotomized animals. Our results indicate that
vagal reflexes contribute a small magnitude of the hyperpnea caused by
carboxyhemoglobinemia. Furthermore, in contrast to that reported for CO2
inhalation, the tachypneic nature of the ventilatory response to CO is not
a vagally mediated phenomenon. CO inhalation had a biphasic influence on
the strength of the lung inflation reflex measured as the ratio of
inspiratory time during occlusion (TIoccl) to inspiratory time of the
preceding spontaneous breath (TIspont). At HbCO levels of 35%,
TIoccl/TIspont was enhanced, whereas at HbCO levels of 55% of ratio fell to
unity, indicating abolition of the reflex. After vagotomy, this ratio was
unity at all levels of carboxyhemoglobinemia.
