Thalamic blood flow and EEG frequency band power during hyperventilation in idiopathic generalized epilepsy

Abstract

AbstractAbsence seizures in idiopathic generalised epilepsy (IGE) involve thalamo-cortical circuits. Hyperventilation (HV) is a standard technique to trigger epileptiform discharges and absence seizures in IGE. HV also increases electroencephalography (EEG) delta band power and decreases global cerebral blood flow (CBF). The relationships between HV, EEG band power, and regional CBF have not been investigated in the same patients at the same time.We compared the effects of hyperventilation between 13 individuals with IGE and 18 healthy controls on thalamic CBF assessed with pseudo-continuous Arterial Spin Labelling (pCASL) simultaneously to EEG frequency band power during three periods of hyperventilation interleaved with three periods of rest, normalised to each participant’s pre-HV values.Pre-HV, there were no differences between patients and controls. During the three rest periods combined, patients had higher normalised respiratory rates but no difference in CBF or EEG band power compared with controls.During HV, CBF decreases were similar in controls and IGE patients in cortical gray matter (37.1±1.3% in controls, 37.9±2.0% in patients) and basal ganglia (35.6±2.0% in controls, 33.3±2.3% in patients). In the thalamus, CBF decreased by 35.5±1.9% in controls, but only by 27.1±2.5% in patients (p=0.011). Delta band power increased by 42% in patients, but only by 27% in patients (p<0.045).Both controls’ and patients’ thalamic CBF significantly decreased as a function of respiratory rate, but the relationship was weaker in patients (rho –0.38 [0.95 confidence interval lower limit −0.629; upper limit −0.059] vs –0.51 [-0.698; −0.255] in controls). Delta power correlated with thalamic CBF only in controls (rho −0.21 [-0.388; −0.017]) but not in patients (rho −0.1 [-0.345; 0.157]). EEG power and respiratory rate were not significantly correlated in either group.This first study of the interrelationships between HV, blood flow, and EEG band power suggests that regional thalamic abnormalities of blood flow regulation, or a neurophysiological abnormality leading to smaller reactive blood flow changes, may underlie HV-associated EEG activation.Graphical abstract textIn this first investigation of combined hyperventilation, blood flow and EEG band power measurements in idiopathic generalised epileptic patients and healthy subjects, we revealed that localized thalamic blood flow regulatory problems or neurophysiological disorders caused minor reactive blood flow variations and may cause hyperventilation-associated EEG activation.