Document Type

Theses, Ph.D

Rights

This item is available under a Creative Commons License for non-commercial use only

Disciplines

3.2 CLINICAL MEDICINE

Publication Details

Thesis successfully submitted to the Dublin Institute of Technology for the award of Doctor of Philosophy, July, 2008.

Abstract

Hyperventilation is used as an activation procedure during EEG. It induces hypocapnia, which elicits changes in brain wave activity that may be diagnostically useful. The mechanism of action by which Hyperventilation (HV) produces slow theta/delta waves on EEG remains conjectural. Four criteria determine the magnitude of HV response: vigorous exchange of air, blood glucose levels, age of subject, and posture. Effects of posture are poor studied quantitatively. Objective: A Standardised Optimal Hyperventilation Protocol (SOHVP), which elicited Hyperventilation Induced High Amplitude Rhythmic Slow activity (HIHARS) during EEG controlling for posture seated (stOHV) and supine (spOHV) is presented and validated. Method: Respiratory rate 30/min, producing three fold elevation in total expiratory vol/min (VE), duration 4 minutes. Cohort of 22 healthy adults subjects, 14 females, 8 males, mean age 29.5 years recruited. Digital video EEG, EOG, EMG, Respiration Rate, Heart Rate,pO2, end tidal pCO2 and Cerebral Blood Flow are monitored before, during and after OHV performed in sitting (st) and supine (sp) position. Results: StOHV is more effective than spOHV in eliciting Hyperventilation Induced High Amplitude Rhythmic Slow activity (HIHARS) on EEG or normal adults, significantly reducing pETCO2 power density of slow EEG frequencies and vCBF. Significance: The role of posture is confirmed as one of the factors influencing magnitude of the HV response. The seated posture is significantly more effective than the supine in developing a standardised hyperventilation response. A prospective clinical trial commenced. Objective: Is seated standardized optimal hyperventilation (StOHV) more effective in eliciting positive EEG findings in patients with Childhood Absence Epilepsy (CAE) and Attack Disorders (AD). Method: Two cohorts, a group of patients with Childhood Absence Epilepsy matched for age and sex with a group of patients with undiagnosed events. 37 patients recruited 19 female 18 male. Mean age 9.7 years. Comparing the number of absence seizures + HIHARS in HV during non standardised (nsHV) and StOHV protocol with those spontaneously occurring during resting, wakefulness and sleep, using 8-minute epochs as denominators. Results: 7 spontaneous CAE events captured at rest, 10 during nsHV and 27 during StOHV. Mean PDR 1.61 Hz slower during STOHV. Discussion: 8.1% patients (18.75% of CAE group) would not have been diagnosed with CAE if STOHV exercise not performed. Significance: The StOHV method is statistically and clinically, more effective than nsHV at eliciting diagnostic epileptiform abnormalities on EEG. Adoption of standardised operational protocol (SOP) recommended as guideline for best practice for EEG testing in clinical practice. Standardized hyperventilation response can separate seizures from other forms of idiopathic changes in metal status in children. A hypothesis for HV induced EEG rhythmogenesis of slow theta and delta is discussed with a role for neuronal-glial interaction at the network level.

DOI

10.21427/D7PW24

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