[Effect of nasal breathing and blockade of the trigeminal nerves on the CO2 concentration in alveolar air in decerebrated cats].

In 14 decerebrated and vagotomized cats, the changes of end tidal CO2 fraction (FET. CO2) and lung ventilation after thermal blockade of the trigeminal nerves, were determined. The values of the lung ventilation and FET,CO2 were compared for breathing through the tracheotomy tube and through the nose. After the trigeminal nerves blockade, FET,CO2 was diminished whereas the lung ventilation increased; the diminution of FET,CO2 was a consequence of the lung ventilation increase. The changes were more evident with nasal rather than tracheal breathing because of cessation of not only tonic afferent impulsation but the impulsation from "flow" receptors in the nose as well. After the onset of nasal breathing the intensity of inhibitory influence of the "flow" receptors was temporarily diminished. Afferent impulses in the trigeminal nerves move the CO2 tension set point to a lower level by depressing the responses of central respiratory mechanism to the chemoreceptor signals.