Response/
Artifact
Mechanism EEG Appearance Localizatio
n
Clinical Relevance
“Built up”
hyperventilatio
n-induced high-
amplitude
rhythmic
slowing
(HIHARS)
CO2 reduction induces
vasoconstriction -> brain
metabolism slows down
Esp active part
High amplitude
theta delta.
The study shows
HV 3 min provide
the maximum
blood flow drop
resolve within 0.5-
1 min
Frontal in
adulthood
Occipital in
children
-Build up response in
>70% in Children but
less (10%) in aging
Absence seizure Likely alkalosis -> PH
sensitive thalamocortical
function rather than
vasoconstriction
Normal
background or
OIRDA 20-30% ->
ictal 3 Hz spike
and wave
Generalized About 90% of
childhood (genetic)
absence - most
triggered within 90
seconds of HV onset
Focal seizure Most are structural esp.
Autoimmune encephalitis.
Most common=
electrographic
seizure
Most =
temporal
Only 0.5% of adult
suspects of seizure
trigger by HV.
Re-built up
+/- hemiplegia
Vasoconstriction ->
transient improve by
compensation ->
insufficient due to
underlying
The delta activity
re happen after >
1 min stop HV
The lesional
hemisphere
Moya Moya disease
(characteristic found in
80-90% of cases)
