Stefanie Gadeyne

Soft, Comfortable Polymer Dry Electrodes for High Quality ECG and EEG Recording

Conventional gel electrodes are widely used for biopotential measurements, despite important drawbacks such as skin irritation, long set-up time and uncomfortable removal. Recently introduced dry electrodes with rigid metal pins overcome most of these problems; however, their rigidity causes discomfort and pain. This paper presents dry electrodes offering high user comfort, since they are fabricated from EPDM rubber containing various additives for optimum conductivity, flexibility and ease of fabrication. The electrode impedance is measured on phantoms and human skin. After optimization of the polymer composition, the skin-electrode impedance is only ∼10 times larger than that of gel electrodes. Therefore, these electrodes are directly capable of recording strong biopotential signals such as ECG while for low-amplitude signals such as EEG, the electrodes need to be coupled with an active circuit. EEG recordings using active polymer electrodes connected to a clinical EEG system show very promising results: alpha waves can be clearly observed when subjects close their eyes, and correlation and coherence analyses reveal high similarity between dry and gel electrode signals. Moreover, all subjects reported that our polymer electrodes did not cause discomfort. Hence, the polymer-based dry electrodes are promising alternatives to either rigid dry electrodes or conventional gel electrodes.

The systemic kainic acid rat model of temporal lobe epilepsy: Long-term EEG monitoring

Animal models reproducing the characteristics of human epilepsy are essential for the elucidation of the pathophysiological mechanisms. In epilepsy research there is ongoing debate on whether the epileptogenic process is a continuous process rather than a step function. The aim of this study was to assess progression of epileptogenesis over the long term and to evaluate possible correlations between SE duration and severity with the disease progression in the kainic acid model. Rats received repeated KA injections (5mg/kg) until a self-sustained SE was elicited. Continuous depth EEG recording started before KA injection and continued for 30 weeks. Mean seizure rate progression could be expressed as a sigmoid function and increased from 1 ± 0.2 seizures per day during the second week after SE to 24.4 ± 6.4 seizures per day during week 30. Seizure rate progressed to a plateau phase 122 ± 9 days after SE. However, the individual seizure rate during this plateau phase varied between 14.5 seizures and 48.6 seizures per day. A circadian rhythm in seizure occurrence was observed in all rats. Histological characterization of damage to the dentate gyrus in the KA treated rats confirmed the presence of astrogliosis and aberrant mossy fiber sprouting in the dentate gyrus. This long-term EEG monitoring study confirms that epileptogenesis is a continuous process rather than a step function.

The Role of Skull Modeling in EEG Source Imaging for Patients with Refractory Temporal Lobe Epilepsy

We investigated the influence of different skull modeling approaches on EEG source imaging (ESI), using data of six patients with refractory temporal lobe epilepsy who later underwent successful epilepsy surgery. Four realistic head models with different skull compartments, based on finite difference methods, were constructed for each patient: (i) Three models had skulls with compact and spongy bone compartments as well as air-filled cavities, segmented from either computed tomography (CT), magnetic resonance imaging (MRI) or a CT-template and (ii) one model included a MRI-based skull with a single compact bone compartment. In all patients we performed ESI of single and averaged spikes marked in the clinical 27-channel EEG by the epileptologist. To analyze at which time point the dipole estimations were closer to the resected zone, ESI was performed at two time instants: the half-rising phase and peak of the spike. The estimated sources for each model were validated against the resected area, as indicated by the postoperative MRI. Our results showed that single spike analysis was highly influenced by the signal-to-noise ratio (SNR), yielding estimations with smaller distances to the resected volume at the peak of the spike. Although averaging reduced the SNR effects, it did not always result in dipole estimations lying closer to the resection. The proposed skull modeling approaches did not lead to significant differences in the localization of the irritative zone from clinical EEG data with low spatial sampling density. Furthermore, we showed that a simple skull model (MRI-based) resulted in similar accuracy in dipole estimation compared to more complex head models (based on CT- or CT-template). Therefore, all the considered head models can be used in the presurgical evaluation of patients with temporal lobe epilepsy to localize the irritative zone from low-density clinical EEG recordings.

EEG source connectivity to localize the seizure onset zone in patients with drug resistant epilepsy

Electrical source imaging (ESI) from interictal scalp EEG is increasingly validated and used as a valuable tool in the presurgical evaluation of epilepsy as a reflection of the irritative zone. ESI of ictal scalp EEG to localize the seizure onset zone (SOZ) remains challenging. We investigated the value of an approach for ictal imaging using ESI and functional connectivity analysis (FC). Ictal scalp EEG from 111 seizures in 27 patients who had Engel class I outcome at least 1 year following resective surgery was analyzed. For every seizure, an artifact-free epoch close to the seizure onset was selected and ESI using LORETA was applied. In addition, the reconstructed sources underwent FC using the spectrum-weighted Adaptive Directed Transfer Function. This resulted in the estimation of the SOZ in two ways: (i) the source with maximal power after ESI, (ii) the source with the strongest outgoing connections after combined ESI and FC. Next, we calculated the distance between the estimated SOZ and the border of the resected zone (RZ) for both approaches and called this the localization error ((i) LEpow and (ii) LEconn respectively). By comparing LEpow and LEconn, we assessed the added value of FC. The source with maximal power after ESI was inside the RZ (LEpow = 0 mm) in 31% of the seizures and estimated within 10 mm from the border of the RZ (LEpow ≤ 10 mm) in 42%. Using ESI and FC, these numbers increased to 72% for LEconn = 0 mm and 94% for LEconn ≤ 10 mm. FC provided a significant added value to ESI alone (p < 0.001). ESI combined with subsequent FC is able to localize the SOZ in a non-invasive way with high accuracy. Therefore it could be a valuable tool in the presurgical evaluation of epilepsy.

Impact of Vagal Nerve Stimulation on Objective Vocal Quality, a Pilot Study

OBJECTIVE The purpose of this study was to determine the impact of vagal nerve stimulation (VNS) on the vocal quality using the dysphonia severity index (DSI). It was hypothesized that the objective vocal quality and other vocal characteristics are disordered in comparison with an age- and gender-matched control group. In addition, the acoustic vocal parameters were compared during three conditions: at rest, during normal stimulation, and raised stimulation. A significant relation between the amount of stimulation and the presence of disturbed acoustic parameters was hypothesized. METHODS Subjective (auditory-perceptual evaluation and voice handicap index) and objective (aerodynamic, vocal range, acoustic measurements and determination of the DSI) measurements were used to determine the vocal quality in 13 subjects with VNS in three different conditions (at rest and during normal and raised stimulation) and the age- and gender-matched control group. RESULTS The subjects with VNS had a disordered perceptual vocal quality mainly characterized by the presence of a moderate roughness and slight breathiness, and the objective vocal quality by means of the DSI value is -2.4. During stimulation and especially during raised stimulation, the fundamental frequency is significantly increased. However, the subjects experienced no psychosocial handicapping effect of the vocal quality on the quality of life. CONCLUSIONS Subjects with VNS have typical vocal characteristics. Ear, nose, and throat specialists and voice therapist must be aware of the presence of this vocal pattern at rest and during normal and raised stimulation. Especially, professional voice users and elite vocal performers must be informed before implantation.

Recent advances in devices for vagus nerve stimulation

ABSTRACT Introduction: Vagus nerve stimulation (VNS) has become a valuable treatment option for refractory epilepsy and depression. To improve clinical efficacy and minimize side effects, novel device technology for VNS is under development and investigation. Areas covered: For epilepsy, the AspireSR®, and SenTiva™ VNS therapy systems are the two most recently developed VNS devices. These novel devices have implemented a closed-loop approach and contain a cardiac based seizure detection algorithm. The mechanism of action of VNS remains to be further elucidated, but as preclinical research reveals VNS induced effects on brain plasticity, the autonomic nervous system and the inflammatory response, the indications of VNS are expanding. VNS devices are currently being investigated for stroke rehabilitation, treatment of chronic heart failure and rheumatoid arthritis. Recently devices to noninvasively affect vagus nerve functioning have been developed, with the aim of achieving similar effects without the drawbacks of a surgical procedure and continuous stimulation. Expert commentary: Several animal and human trials have shown promising results with minimal adverse events. However, further research needs to be conducted to validate the use of these devices and decide on optimal stimulation parameters.

Automated long-term EEG analysis to localize the epileptogenic zone

We investigated the performance of automatic spike detection and subsequent electroencephalogram (EEG) source imaging to localize the epileptogenic zone (EZ) from long‐term EEG recorded during video‐EEG monitoring.

LP6: Ictal tachycardia in childhood epilepsy

Results: Out of all examined patients with epilepsy and a specific comorbid disease, 916 (56.4%) patients have diffuse changes in the background activity, 32 (2%) patients have generalized paroxysmal activity, 157 (9.6%) patients have disorganized background activity with generalized paroxysmal activity, 591 (32%) of the patients have focal activity. There is a dependency between the EEG changes of some most often encountered somatic and neurological diseases. Conclusions: The presence of comorbid diseases relates to a higher risk for aggravating the condition of the patient, increasing the EEG changes, a presence of interdependence between the separate diseases, as well as between their treatment.