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Ictal cerebral haemodynamic characteristics during typical absence seizures, compared to focal seizures with brief alteration of awareness Volume 21, numéro 3, June 2019

TEST YOURSELF

(1) Absence seizures are clearly identified using vEEG; what is the value of the dynamic curve of CBF?

(2) How do you explain the difference between the haemodynamic characteristics during TAS and BCPS?

(3) Why are absence seizures easily induced during hyperventilation?

 

 

 

 

 

 

 

 

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Answers

(1) The dynamic curve of CBF is a more intuitive tool, and the screen does not have to be switched. Moreover, knowledge of the analysis of the dynamic curve can be easily acquired.

 

(2) The different haemodynamic characteristics between TAS and BCPS may reflect different pathophysiological mechanisms and networks. The thalamocortical system is mostly considered as an oscillating network of TAS, while in focal epileptogenic lesions, the overexcitation of cortical neurons increases metabolic demand and results in an increase in cortical CBF.

 

(3) Because the thalamocortical system (excitation of thalamic neurons and inhibition of cortical neuronal activity) is mostly considered as an oscillating network generating neurophysiological rhythms associated with TAS, the thalamus is more tolerant of hypoxia than the cortex. Hyperventilation leads to hypocapnia and a resultant decrease in CBF to the cortex; excitability of thalamic neurons exists but cortical neuronal activity is inhibited. TAS are more apt to be evoked by hyperventilation. This has been confirmed by the ictal cerebral haemodynamic characteristics during spontaneous typical absence seizures and hyperventilation-evoked absence seizures.

 

 

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