Elena Urrestarazu

Independent component analysis as a tool to eliminate artifacts in EEG: A quantitative study

Summary Independent component analysis (ICA) is a novel technique that calculates independent components from mixed signals. A hypothetical clinical application is to remove artifacts in EEG. The goal of this study was to apply ICA to standard EEG recordings to eliminate well-known artifacts, thus quantifying its efficacy in an objective way. Eighty samples of recordings with spikes and evident artifacts of electrocardiogram (EKG), eye movements, 50-Hz interference, muscle, or electrode artifact were studied. ICA components were calculated using the Joint Approximate Diagonalization of Eigen-matrices (JADE) algorithm. The signal was reconstructed excluding those components related to the artifacts. A normalized correlation coefficient was used as a measure of the changes caused by the suppression of these components. ICA produced an evident clearing-up of signals in all the samples. The morphology and the topography of the spike were very similar before and after the removal of the artifacts. The correlation coefficient showed that the rest of the signal did not change significantly. Two examiners independently looked at the samples to identify the changes in the morphology and location of the discharge and the artifacts. In conclusion, ICA proved to be a useful tool to clean artifacts in short EEG samples, without having the disadvantages associated with the digital filters. The distortion of the interictal activity measured by correlation analysis was minimal.

Independent component analysis removing artifacts in ictal recordings

Summary:  Purpose: Independent component analysis (ICA) is a novel algorithm able to separate independent components from complex signals. Studies in interictal EEG demonstrate its usefulness to eliminate eye, muscle, 50‐Hz, electrocardiogram (ECG), and electrode artifacts. The goal of this study was to evaluate the usefulness of ICA in removing artifacts in ictal recordings with a known EEG onset.

Sleep loss as risk factor for neurologic disorders: A review

Sleep loss refers to sleep of shorter duration than the average baseline need of seven to eight hours per night. Sleep loss and sleep deprivation have severe effects on human health. In this article, we review the main aspects of sleep loss, taking into account its effects on the central nervous system. The neurocognitive and behavioral effects of sleep loss are well known. However, there is an increasing amount of research pointing to sleep deprivation as a risk factor for neurologic diseases, namely stroke, multiple sclerosis, Alzheimers disease, headache, epilepsy, pain, and somnambulism. Conversely, sleep loss has been reported to be a potential protective factor against Parkinsons disease. The pathophysiology involved in this relationship is multiple, comprising immune, neuroendocrine, autonomic, and vascular mechanisms. It is extremely important to identify the individuals at risk, since recognition and adequate treatment of their sleep problems may reduce the risk of certain neurologic disorders.

Changes in the Heart Rate Variability in Patients with Obstructive Sleep Apnea and Its Response to Acute CPAP Treatment

Introduction Obstructive Sleep Apnea (OSA) is a major risk factor for cardiovascular disease. The goal of this study was to demonstrate whether the use of CPAP produces significant changes in the heart rate or in the heart rate variability of patients with OSA in the first night of treatment and whether gender and obesity play a role in these differences. Methods Single-center transversal study including patients with severe OSA corrected with CPAP. Only patients with total correction after CPAP were included. Patients underwent two sleep studies on consecutive nights: the first night a basal study, and the second with CPAP. We also analyzed the heart rate changes and their relationship with CPAP treatment, sleep stages, sex and body mass index. Twenty-minute segments of the ECG were selected from the sleep periods of REM, no-REM and awake. Heart rate (HR) and heart rate variability (HRV) were studied by comparing the R-R interval in the different conditions. We also compared samples from the basal study and CPAP nights. Results 39 patients (15 females, 24 males) were studied. The mean age was 50.67 years old, the mean AHI was 48.54, and mean body mass index was 33.41 kg/m2 (31.83 males, 35.95 females). Our results showed that HRV (SDNN) decreased after the use of CPAP during the first night of treatment, especially in non-REM sleep. Gender and obesity did not have any influence on our results. Conclusions These findings support that cardiac variability improves as an acute effect, independently of gender or weight, in the first night of CPAP use in severe OSA patients, supporting the idea of continuous use and emphasizing that noncompliance of CPAP treatment should be avoided even if it is just once.

Late-onset periodic asystolia during vagus nerve stimulation.

Cardiac changes may occasionally occur during vagus nerve stimulation (VNS) used in epileptic patients. As they can be potentially life‐threatening, it is important to detect them, and this is why an intraoperative test is performed during the implantation. Few cases of asystole during this test have been described. Only one patient with late‐onset bradyarrythmia caused by VNS has been reported. This patient had been implanted 2 years and 4 months before the episode. We present another case of late asystole in a patient whose VNS had been implanted 9 years before the arrhythmia onset. In our patient, each run of stimulation produced bradyarrhythmias and very often severe asystolia due to atrium‐ventricular block.

Beta Activity in the Subthalamic Nucleus During Sleep in Patients with Parkinson's Disease

The recordings of local field potentials in the subthalamic nucleus in patients with Parkinsons disease (PD), carried out through the stimulators implanted to treat the motor symptoms of the disease, show a prominent basal (“off”) activity in the beta range, which is attenuated after dopaminergic therapy. A recent study described improvement of parkinsonian features during rapid eyes movements (REM) sleep. We describe, for the first time, the changes in activity of the subthlamic nucleus (STN) during different sleep stages in Parkinsons disease with special interest in the beta band. Ten patients with PD treated with deep brain stimulation of the STN were studied. Subthalamic local field potentials (LFPs) were recorded through the stimulation electrodes during wakefulness (“off” medication) and different sleep stages. In Stage 2 and slow‐wave sleep, a significant decrease of beta activity was recorded. During REM sleep, beta power values were similar to wakefulness values or even higher. These findings indicate that STN activity is modulated and modified during different sleep stages. The increased beta activity during REM sleep is a new but unexpected finding, which requires further analysis.

Clinical management of sleep disturbances in Alzheimer's disease: current and emerging strategies

Sleep and circadian disorders in Alzheimer’s disease (AD) are more frequent than in the general population and appear early in the course of the disease. Quality of sleep and quality of life are parallel in these patients, and such disorders also represent a heavy burden for caregivers. Although alterations in melatonin and hypocretins (orexins) seem to play a key role in the origin of these disturbances, the etiology of these disorders is multifactorial, including many factors such as environment, behavior, treatments, and comorbidities, among others. A comprehensive evaluation of sleep in each patient is essential in the design of the treatment that includes nonpharmacological and pharmacological approaches. One particularly interesting point is the possibility of a role of sleep disorders in the pathogenesis of AD, raising the possibility that treating the sleep disorder may alter the course of the disease. In this review, we present an update on the role of sleep disorders in AD, the bidirectional influence of sleep problems and AD, and treatment options. Behavioral measures, bright light therapy (BLT), melatonin, and other drugs are likely well known and correctly managed by the physicians in charge of these patients. In spite of the multiple treatments used, evidence of efficacy is scarce and more randomized double-blind placebo-controlled studies are needed. Future directions for treatment are the establishment of BLT protocols and the development of drugs with new mechanisms of action, especially hypocretin receptor antagonists, melatonin receptor agonists, and molecules that modulate the circadian clock.

Increased Sympathetic and Decreased Parasympathetic Cardiac Tone in Patients with Sleep Related Alveolar Hypoventilation

OBJECTIVE To assess autonomic function by heart rate variability (HRV) during sleep in patients with sleep related alveolar hypoventilation (SRAH) and to compare it with that of patients with obstructive sleep apnea (OSA) and control patients. DESIGN Cross-sectional study. SETTING Sleep Unit, University Hospital of University of Navarra. PATIENTS Fifteen idiopathic and obesity related-SRAH patients were studied. For each patient with SRAH, a patient with OSA, matched in age, sex, body mass index (BMI), minimal oxygen saturation (SatO2), and mean SatO2 was selected. Control patients were also matched in age, sex, and BMI with patients with OSA and those with SRAH, and in apnea/hypopnea index (AHI) with patients with SRAH. INTERVENTIONS N/A. MEASUREMENTS AND RESULTS Time- and frequency-domain HRV measures (R-R, standard deviation of normal-to-normal RR interval [SDNN], very low frequency [VLF], low frequency [LF], high frequency [HF], LF/HF ratio) were calculated across all sleep stages as well as during wakefulness just before and after sleep during a 1-night polysomnography. In patients with SRAH and OSA, LF was increased during rapid eye movement (REM) when compared with control patients, whereas HF was decreased during REM and N1-N2 sleep stages. The LF/HF ratio was equally increased in patients with SRAH and OSA during REM and N1-N2. Correlation analysis showed that LF and HF values during REM sleep were correlated with minimal SatO2 and mean SatO2. CONCLUSIONS Patients with SRAH exhibited an abnormal cardiac tone during sleep. This fact appears to be related to the severity of nocturnal oxygen desaturation. Moreover, there were no differences between OSA and SRAH, supporting the hypothesis that autonomic changes in OSA are primarily related to a reduced nocturnal oxygen saturation, rather than a consequence of other factors such as nocturnal respiratory events.

Spasm of the sternocleidomastoid muscle induced by vagal nerve stimulation

Vagal nerve stimulation (VNS) is a recently introduced treatment for drug-resistant epilepsies.1 Both partial and generalized seizures, especially atonic, may improve with this device, although the mechanism of action is not clearly understood. Approximately one third of patients treated with VNS have had a 50% reduction in the frequency of their seizures, thus making a significant impact on their quality of life.1 Efficacy has been related to the intensity of the stimulation. Side effects are generally infrequent and mild. They may be produced by the stimulation or the implant procedure. Voice alteration, hoarseness, dysphonia, cough, pain, dyspnea, vomiting, nausea, hiccups, paresthesia, fever, local infection, accidental injury, aspiration, and bradycardia have been quoted as side effects.1-3⇓⇓ Bradycardia is avoided by placing the stimulator by the left vagal nerve; however, even with this precaution, asystolia has been reported.4,5⇓ These complications usually did not lead to termination of the therapy. The occurrence of sudden death in these patients was not greater than in other epileptic patients.6 Overall, VNS treatment has proved to be safe, efficient, and cost-beneficial. A patient had a spasm of the sternocleidomastoid (SCM) when the stimulation intensity reached 2 mA. Clinically it was similar to an episodic torticollis. …

Independent component analysis separates spikes of different origin in the EEG.

Summary: Independent component analysis (ICA) is a novel system that finds independent sources in recorded signals. Its usefulness in separating epileptiform activity of different origin has not been determined. The goal of this study was to demonstrate that ICA is useful for separating different spikes using samples of EEG of patients with focal epilepsy. Digital EEG samples from four patients with focal epilepsy were included. The patients had temporal (n = 2), centrotemporal (n = 1) or frontal spikes (n = 1). Twenty-six samples with two (or more) spikes from two different patients were created. The selection of the two spikes for each mixed EEG was performed randomly, trying to have all the different combinations and rejecting the mixture of two spikes from the same patient. Two different examiners studied the EEGs using ICA with JADE paradigm in Matlab platform, trying to separate and to identify the spikes. They agreed in the correct separation of the spikes in 24 of the 26 samples, classifying the spikes as frontal, temporal or centrotemporal, left or right sided. The demonstration of the possibility of detecting different artificially mixed spikes confirms that ICA may be useful in separating spikes or other elements in real EEGs.