THE INFLUENCE OF HYPERPNEA AND OF VARIATIONS OF O2- AND CO2-TENSION IN THE INSPIRED AIR UPON HEARING

Abstract

In 96 exps. on 6 human subjects the vestibular nerve received a caloric stimulation (procedure of Veits). Breathing of CO2-air-mixtures (5-7%) reduced the number of nystagmic movements, whereas hyperpnea caused an increase. The brain stem, therefore, reacts to increases and decreases in the CO2-tension of the blood with the same direction of change in excitability as occurs in spinal reflexes. O2-lack produces an effect on the nystagmus (decrease in no.) only under the conditions of severe anoxemia. The effects are temporary, and as soon as 3 min. afterward control values are obtained. These reactions are strikingly different from those observed in the more strictly cortical processes reported earlier. The differences appear to be largely associated with the relative sensitivity to O2-lack. The cortical neurones are extremely sensitive to alterations in O2 supply, while the brain stem centers studied, either because of a more adequate blood supply or for other reasons, are relatively insensitive to such changes.