Post-hyperventilation Apnea with Spindle Activity on Electroencephalogram

Loss of consciousness occurs in post-hyperventilation apnea, but its pathophysiology remains unclear. We herein report a patient with post-hyperventilation apnea showing spindle activity on electroencephalogram (EEG). The patient was alert and breathing spontaneously before the hyperventilation test, but loss of consciousness and apnea with spindle activity on EEG occurred when the end-tidal CO(2) decreased during the hyperventilation test. She recovered consciousness and spontaneous breathing with the disappearance of the spindle activity on EEG when the end-tidal CO(2) increased after the hyperventilation test. The loss of consciousness during post-hyperventilation apnea might be due to the focal involvement of the ascending-activating mesodiencephalic reticular formation.