Inspiratory facilitatory and inhibitory vagal influences during apnoea in rabbits

During hyperventilation apnoea in vagotomized, anaesthetized rabbits, paralyzed and artificially ventilated, the effects of electrical afferent stimulation of the vagus nerve on the provocation and inhibition of inspiratory activity were investigated. The experiments were repeated using hyperinflation or short-lasting inflation in nonvagotomized animals. It was found that the possibility of observing inspiratory facilitatory phenomena depended on the interrelationship between the frequency of impulses transmitted separately through the thick and thin myelinated fibres. The time constants of central summation of vagal information and the possibility of observation of the phenomena of inspiratory facilitation depended on the central respiratory drive changed by CO2 and temperature.