QUANTITATIVE EEG CHANGES UNDER VARIOUS CONDITIONS OF HYPERVENTILATION IN THE SENSORIMOTOR CORTEX OF THE ANESTHETIZED CAT

The effects on the EEG rhythms recorded from the sensorimotor cortex (post-sigmoid gyrus) of anaesthetized cats were studied under 4 conditions of artificial mechanical hyperventilation (HV) before and after cervical bilateral vagotomy. In animals with intact vagus nerves, using visual examination, EEG changes were only observed within the 2nd min during HV produced by increased stroke volume (DELTA-V) with associated hypocapnia. Quantitative EEG (qEEG) showed that, for the same increase in minute ventilation and the same degree of hypocapnia, DELTA-V induced a greater and earlier relative decrease (2nd min) in the power density of delta, theta and alpha bands, than increased pump frequency (DELTA-F). The DELTA-F tests produced a fall only in the theta band and within the 3rd min. With constant p(a)CO2, transient modifications occurred only with DELTA-V and were limited to the first 30 sec. In bivagotomized cats, moderate EEG responses to DELTA-V plus associated hypocapnia persisted partly in the alpha band. Finally, no changes appeared with DELTA-V or DELTA-F when the vagus nerves were cut and p(a)CO2 was maintained constant. The present data suggest strongly that, in anaesthetized cats, peripheral vagal afferents from the respiratory system play a major role in the EEG changes caused by artificial hyperventilation.