DOES CO2 ACT ON THE RESPIRATORY CENTERS

In cats anaesthetized with chloralose and urethane the central chemosensitivity was reversibly blocked by cooling or abolished by coagulation of the intermediate area (S) on the ventral surface of the medulla oblongata which is considered as a point of convergence of the central chemosensory impulse traffic. The peripheral chemoreceptor afferents were severed and rhythmic respiration was maintained by either continuous or rhythmic stimulation of the carotid sinus nerves. In this situation with the cats breathing oxygen, sensitivity to CO2 was tested by inhalation of CO2 in oxygen. The respiration induced by stimulation was not dependent upon pACO2 in any of the seven cats tested. After a prolonged period of cooling or after coagulation a rhythmic respiration with small amplitude and high frequency reappeared. This type of respiration was also independent of CO2. Later, in some experiments, the amplitude of this breathing pattern increased and became slightly dependent on CO2 with increasing pACO2. The frequency increased more clearly than the amplitude. These effects were interpreted as a reactivation of superficial chemosensitive structures. It is concluded that after interruption of the central chemosensory afferents the remaining central structures (the respiratory centers) do not react to CO2 or H+ in any degree significant for respiratory regulation. © 1979 Springer-Verlag.