Quantitative EEG changes due to hypobaric hypoxia in normal subjects.

A condition of hypobaric hypoxia was created in a low pressure chamber by reducing the atmospheric pressure to 46.5 kPa. Thirty-six subjects were exposed to hypobaric hypoxia during 19 min with a recovery period of 25 min. In 13 subjects the experiment was repeated after 1 week. Four EEG channels, HbSaO2, PeCO2, heart and respiration rate were continuously monitored. Quantitative EEG (qEEG) samples for the derivation P4-O2 were taken in normobaric normoxic (A), hypobaric normoxic (B) and hypobaric hypoxic (C) conditions and mutually compared. Subtraction spectra and standard qEEG parameters were studied, in an attempt to select those which are most reliable to detect hypoxia. Hypobaric normoxia caused no significant qEEG changes. Hypobaric hypoxia resulted in a significant increase in slow activity, a significant decrease in alpha activity and a non-significant decrease in beta activity. Two clusters of non-related standard qEEG parameters were found to be sensitive to hypoxia. The differences between the parameters within each cluster are too small to permit a definite choice of one of them. For the description of qEEG changes due to hypoxia at least one parameter from each cluster has to be taken into account.