Biomedical subjects

P LeVan

Publications and source records attributed to P LeVan.

4 recordsLinked to original sources

PubMed2006

High-frequency oscillations during human focal seizures.

Discrete high-frequency oscillations (HFOs) in the range of 100-500 Hz have previously been recorded in human epileptic brains using depth microelectrodes. We describe for the first time similar oscillations in a cohort of unselected focal epileptic patients implanted with EEG macroelectrodes. Spectral analysis and visual inspection techniques were used to study seizures from 10 consecutive patients undergoing pre-surgical evaluation for medically refractory focal epilepsy. Four of these patients had focal seizure onset in the mesial temporal lobe, and in all 12 of their seizures, well-localized, segmental, very high frequency band (VHF: 250-500 Hz) oscillations were visually identified near the time of seizure onset from contacts in this zone. Increased high-frequency band (HF: 100-200 Hz) activity compared with the background was distinguished both visually and with spectral analysis later in the seizures of 3/4 mesial temporal patients, involving contacts in the generator region and, in one patient, areas of contralateral peri-hippocampal propagation. Three patients with well-defined neocortical seizure-onset areas also demonstrated focal HF or VHF oscillations confined to the seizure-onset channels during their eight seizures. No discrete HF or VHF activity was present in the poorly localized seizures from the remaining three patients. These results show that discrete HFOs can be recorded from human focal epileptic brain using depth macroelectrodes, and that they occur mostly in regions of primary epileptogenesis and rarely in regions of secondary spread. Absent high-frequency activity seems to indicate poor localization, whereas the presence of focal HFOs near the time of seizure onset may signify proximity to the epileptogenic focus in mesial temporal lobe and neocortical seizures. We postulate that focal HFOs recorded with depth macroelectrodes reflect the partial synchronization of very local oscillations such as those previously studied using microelectrodes, and result from interconnected small neuronal ensembles. Our finding that localized HFOs occur in varying anatomical structures and pathological conditions perhaps indicates commonality to diverse epileptogenic aetiologies.

Adult↗

PubMed2006

Independent component analysis identifies ictal bitemporal activity in intracranial recordings at the time of unilateral discharges.

OBJECTIVE: To apply independent component analysis (ICA) in intracranial recordings to analyze interactions during temporal lobe seizures. METHODS: Seizures from 20 patients with bitemporal implantation were classified as unilateral or bilateral and analyzed with ICA. During the period preceding bilateral activity, correlation coefficients were calculated between ICA components having ictal activity during the unilateral seizure phase (early ICA components) and every channel of the original EEG. ICA components were classified as unilateral if the correlation was >0.2 exclusively with channels in one hemisphere; and bilateral if both hemispheres were involved. RESULTS: One hundred twenty-three seizures were analyzed. Thirty-two percent of visually classified unilateral seizures and 64% of bilateral seizures (during the unilateral phase) had bilateral ICA components. The proportion of early ICA components that were bilateral and the proportion of channels contralateral to the visually identified seizure with correlation higher than 0.2 with at least one early ICA component were significantly lower in seizures that stayed unilateral than in seizures that later became bilateral by visual inspection (11 and 10%, respectively, in unilateral seizures; 33 and 28% in bilateral seizures; P=0.001). CONCLUSIONS: In patients with bitemporal epilepsy, approximately 20% of the components extracted using ICA have a bitemporal distribution even at the time when the seizures are apparently unilateral. The presence of early contralateral ictal activity is more frequent and extensive in seizures that later become evidently bilateral. SIGNIFICANCE: Minimal contralateral seizure activity is present even when the discharge appears unilateral and this is more frequent in seizures which later spread to the contralateral temporal lobe.

Adult↗

PubMed2006

A system for automatic artifact removal in ictal scalp EEG based on independent component analysis and Bayesian classification.

OBJECTIVE: To devise an automated system to remove artifacts from ictal scalp EEG, using independent component analysis (ICA). METHODS: A Bayesian classifier was used to determine the probability that 2s epochs of seizure segments decomposed by ICA represented EEG activity, as opposed to artifact. The classifier was trained using numerous statistical, spectral, and spatial features. The system's performance was then assessed using separate validation data. RESULTS: The classifier identified epochs representing EEG activity in the validation dataset with a sensitivity of 82.4% and a specificity of 83.3%. An ICA component was considered to represent EEG activity if the sum of the probabilities that its epochs represented EEG exceeded a threshold predetermined using the training data. Otherwise, the component represented artifact. Using this threshold on the validation set, the identification of EEG components was performed with a sensitivity of 87.6% and a specificity of 70.2%. Most misclassified components were a mixture of EEG and artifactual activity. CONCLUSIONS: The automated system successfully rejected a good proportion of artifactual components extracted by ICA, while preserving almost all EEG components. The misclassification rate was comparable to the variability observed in human classification. SIGNIFICANCE: Current ICA methods of artifact removal require a tedious visual classification of the components. The proposed system automates this process and removes simultaneously multiple types of artifacts.

Algorithms↗

PubMedDate not supplied

Quantification of interventions and outcomes in an outpatient telemanagement and care management congestive heart failure program.

The congestive heart failure continuum was developed in collaboration with the medical management committee of our hospital in response to a need to decrease readmissions for this chronic and progressive disease. This is accomplished via a multidisciplinary team that provides education and long-term telemanagement, as well as care management to assist these patients in maintaining an optimum level of functioning and the ability to remain in their homes for as long as possible. Since October 1996 there have been 375 patients referred with a decrease in the 31-day readmission rate from 21% to an average of 5%. Costs are presently $55.00 per month per patient. Evaluation of the congestive heart failure phone management tool revealed a strong 77% positive correlation between the patient's score and the number of interventions needed to stabilize the patient. Care management visits, when necessary, help reduce the need for hospitalization. (c)2000 by CHF, Inc.

Journal Article↗