Ventilatory response of the conscious or anesthetized cat to oxygen breathing.

In conscious intact cats, oxygen breathing for up to 1 h does not modify ventilation, and the ventilatory response to CO2 in hyperoxia is not consistently decreased. However, oxygen breathing induces sustained hyperventilation in conscious cats after carotid body denervation. In anesthetized cats, oxygen breathing provokes a hypoventilation which is transient under light anesthesia but more sustained under deeper levels of anesthesia. At all levels of anesthesia, the ventilatory response to CO2 is decreased in hyperoxia as compared with normoxia. These results suggest that: the effects of hyperoxia include a central stimulating component, seen only in conscious animals, which offsets the decreased ventilatory drive from peripheral chemoreceptors; this central component is sensitive to anesthesia, thus allowing an explanation for the permanent decrease in ventilation and decrease in ventilatory response to CO2 observed when oxygen is given during deep anesthesia; and anesthesia may help to purposefully unmask factors involved in the control of breathing, but it markedly alters the normal functioning of the respiratory network.