Quantitative topographical analysis of EEG during nonstandardized and standardized hyperventilation

The aim of this study was to compare the topographical quantitative EEG (qE EG) changes induced by nonstandardized hyperventilation and those induced b y standardized hyperventilation (with the end-tidal PCO2 being maintained a t 2 kPa [15 mm Hg]). We examined 18 healthy volunteers during nonstandardiz ed and 20 during standardized hyperventilation. During nonstandardized hype rventilation, the mean spectral power density in this group significantly i ncreased 1.9 fold within the delta-, 2.2 fold within the theta-, 1.8 fold w ithin the alpha-, and 1.9 fold within the beta-frequency band. There was no significant change of the power ratio and was no topographic difference be tween 4 frequency bands investigated. During standardized hyperventilation, the mean spectral power density in the group significantly increased to 12 .9 fold within the delta-, to 7.6 fold within the theta-, to 1.4 fold withi n the alpha-, and to 2.4 fold within the beta frequency band. The power rat io decreased significantly. Such a pronounced EEG slowing with delta and th eta augmentation was never found during nonstandardized hyperventilation. W e conclude that a consistent slowing of the qEEG in all leads including a c onstant topographical maximum can only be induced by standardized, sufficie ntly pronounced hyperventilation.