Effect of hyperventilation on electroencephalographic activity

To observe the effect of voluntary hyperventilation on electroencephalographic activity during routine EEG recording on patients referred to a tertiary care hospital. This was an observational study conducted at Neurophysiology Lab, Department of Neurology at Liaquat National Hospital, Karachi from May 2007 to September 2007. Data of 326 patients was collected prospectively and analyzed by SPSS version 10.0. At least 3 minutes voluntary hyperventilation was performed by the subjects. All those patients who were able to perform voluntary hyperventilation adequately were included in the study. Of 326 recordings, 256 (78.8%) were normal and 69 (21.2%) were abnormal. Focal epileptiform discharges were identified in 8.6% and generalized in 8.3% of subjects. Physiological slowing was found in 31 records. Out of 55 epileptics, 3 had discharges only during HV and 9 had increase in epileptiform discharges. Hyperventilation has significant effect on background rhythm during EEG recording. It is a useful activation method utilized to increase the yield of EEG.