Spurious electroencephalographic activity due to pulsation artifact in the depth of anesthesia monitor.

BACKGROUND: The depth of anesthesia (DOA) is estimated based on the anesthesia-induced electroencephalogram (EEG) changes. However, the surgical environment, as well as the patient him/herself, generates electrical interferences that cause EEG waveform distortion. CASE PRESENTATION: A 52-year-old patient required general anesthesia due to the right femur necrotizing fasciitis. He had no history of epilepsy or head injury. His cardiovascular status was stable without arrhythmia under propofol and remifentanil anesthesia. The DOA was evaluated with Root® with SedLine® Brain Function Monitoring (Masimo Inc, Irvine, CA). The EEG showed a rhythmic, heart rate time-locked pulsation artifact, which diminished after electrode repositioning. Offline analysis revealed that the pulse wave-like interference in EEG was observed at the heart rate frequency. CONCLUSIONS: We experienced an anesthesia case that involves a pulsation artifact generated by the superficial temporal artery contaminating the EEG signal. Numerous clinical conditions, including pulsation artifact, disturb anesthesia EEG.

Patient-Specific Seizure Detection Using Nonlinear Dynamics and Nullclines.

Nonlinear dynamics has recently been extensively used to study epilepsy due to the complex nature of the neuronal systems. This study presents a novel method that characterizes the dynamic behavior of pediatric seizure events and introduces a systematic approach to locate the nullclines on the phase space when the governing differential equations are unknown. Nullclines represent the locus of points in the solution space where the components of the velocity vectors are zero. A simulation study over 5 benchmark nonlinear systems with well-known differential equations in three-dimensional exhibits the characterization efficiency and accuracy of the proposed approach that is solely based on the reconstructed solution trajectory. Due to their unique characteristics in the nonlinear dynamics of epilepsy, discriminative features can be extracted based on the nullclines concept. Using a limited training data (only 25% of each EEG record) in order to mimic the real-world clinical practice, the proposed approach achieves 91.15% average sensitivity and 95.16% average specificity over the benchmark CHB-MIT dataset. Together with an elegant computational efficiency, the proposed approach can, therefore, be an automatic and reliable solution for patient-specific seizure detection in long EEG recordings.

Electroencephalographic signals during anesthesia recorded from surface and depth electrodes.

PURPOSE: Anesthesiologists have increasingly started to use EEG-based indexes to estimate the level and type of unconsciousness. However, the physiology and biophysics are poorly understood in anesthesiological literature. METHODS: EEG was recorded from electrodes on the surface of head, including scalp, as well as DBS (deep brain stimulation) electrodes implanted deep in the brain. Mathematical modeling with a realistic head model was performed to create illustrative images of the sensitivity of electrode montages. RESULTS: EEG pattern of anesthesia, burst-suppression, is recordable outside of scalp area as well in the depth of brain because the EEG current loops produce recordable voltage gradients in the whole head. The typical electrodes used in anesthesia monitoring are most sensitive to basal surface of frontal lobes as well as frontal and mesial parts of temporal lobes. CONCLUSIONS: EEG currents create closed-loops, which flow from the surface of the cortex and then return to the inside of the hemispheres. In the case of widespread synchronous activity like physiological sleep or anesthesia, the currents recorded with surface and depth electrodes return through the base of brain and skull.

Epileptiform and periodic EEG activities induced by rapid sevoflurane anaesthesia induction.

OBJECTIVES: The aim of the study was to compare the EEG findings and haemodynamic parameters of adult male patients while undergoing mask induction with sevoflurane anaesthesia with either controlled hyperventilation (CH) or spontaneous breathing (SB). METHODS: Twenty male patients, aged 23-52 (mean 42) years were anaesthetized randomly with either spontaneous breathing or mild controlled hyperventilation via mask. EEG was recorded using a full 10-20 electrode set. RESULTS: Anaesthesia induction with high inhaled concentrations of sevoflurane produced several epileptiform and periodic EEG patterns. CH doubled the amount of these EEG patterns compared to SB. Higher heart rate was recorded in the CH group. CONCLUSIONS: We describe a high incidence of paroxysmal EEG activity: epileptiform and generalized periodic discharges (GPDs) during rapid sevoflurane in nitrous oxide-oxygen mask induction in hyperventilated male patients. However these activities have no effect to the heart rate or the mean arterial pressure. SIGNIFICANCE: The monitoring of GPDs and burst suppression patterns during rapid anaesthesia induction with sevoflurane provides possibility to study the effects of volatile anaesthetics in the healthy brain. In order to analyse the different sources of EEG patterns a wide-band multichannel EEG recording is necessary.

Synchronization of brain activity during induction of propofol anesthesia: Comparison of methods.

Synchrony patterns between the EEG measured from the subthalamic nucleus and scalp are analyzed during induction of propofol anesthesia. Various methods such as Coherence, Phase Locking Value, Partial Directed Coherence, Mutual Information, and Transfer Entropy are applied. The results indicate that, in general, the synchrony patterns seen in the depth-scalp electrode pair are similar to those seen between two scalp electrodes of opposite hemispheres. A clear change of state is revealed at about 10 minutes before burst suppression; this event is revealed by linear (Coherence) as well as nonlinear (Phase Locking Value) and information theoretic (Mutual Information and Transfer Entropy) measures. The results suggest that relatively large depth electrodes such as those used in the treatment of the Parkinson's disease are predominantly sensitive to cortical activity.

Novel wireless electroencephalography system with a minimal preparation time for use in emergencies and prehospital care.

BACKGROUND: Although clinical applications such as emergency medicine and prehospital care could benefit from a fast-mounting electroencephalography (EEG) recording system, the lack of specifically designed equipment restricts the use of EEG in these environments. METHODS: This paper describes the design and testing of a six-channel emergency EEG (emEEG) system with a rapid preparation time intended for use in emergency medicine and prehospital care. The novel system comprises a quick-application cap, a device for recording and transmitting the EEG wirelessly to a computer, and custom software for displaying and streaming the data in real-time to a hospital. Bench testing was conducted, as well as healthy volunteer and patient measurements in three different environments: a hospital EEG laboratory, an intensive care unit, and an ambulance. The EEG data was evaluated by two experienced clinical neurophysiologists and compared with recordings from a commercial system. RESULTS: The bench tests demonstrated that the emEEG system's performance is comparable to that of a commercial system while the healthy volunteer and patient measurements confirmed that the system can be applied quickly and that it records quality EEG data in a variety of environments. Furthermore, the recorded data was judged to be of diagnostic quality by two experienced clinical neurophysiologists. CONCLUSIONS: In the future, the emEEG system may be used to record high-quality EEG data in emergency medicine and during ambulance transportation. Its use could lead to a faster diagnostic, a more accurate treatment, and a shorter recovery time for patients with neurological brain disorders.

Classification of EEG bursts in deep sevoflurane, desflurane and isoflurane anesthesia using AR-modeling and entropy measures.

A study relating signal patterns of burst onsets in burst suppression EEG to the anesthetic agent or anesthesia induction protocol is presented. A dataset of 82 recordings of sevoflurane, isoflurane and desflurane anesthesia underlies the study. 3 second segments from the onset of altogether 3214 bursts are described using AR model parameters, spectral entropy and sample entropy as features. The features are clustered using the K-means algorithm. The results indicate that no clear cut distinction can be made between the burst patterns induced by the mentioned anesthetics although bursts of certain properties are more common in certain patient groups. Several directions for further investigations are proposed based on visual inspection of the recordings.

A characteristic time sequence of epileptic activity in EEG during dynamic penicillin-induced focal epilepsy--a preliminary study.

Penicillin-induced focal epilepsy is a well-known model in experimental epilepsy. However, the dynamic evolution of waveforms, DC-level changes, spectral content and coherence are rarely reported. Stimulated by earlier fMRI findings, we also seek for the early signs preceding spiking activity from frequency domain of EEG signal. In this study, EEG data is taken from previous EEG/fMRI series (six pigs, 20-24kg) of an experimental focal epilepsy model, which includes dynamic induction of epileptic activity with penicillin (6000IU) injection into the somatosensory cortex during deep isoflurane anaesthesia. No ictal discharges were recorded with this dose. Spike waveforms, DC-level, time-frequency content and coherence of EEG were analysed. Development of penicillin induced focal epileptic activity was not preceded with specific spectral changes. The beginning of interictal spiking was related to power increase in the frequencies below 6Hz or 20Hz, and continued to a widespread spectral increase. DC-level and coherence changes were clear in one animal. Morphological evolution of epileptic activity was a collection of the low-amplitude monophasic, bipolar, triple or double spike-wave forms, with an increase in amplitude, up to large monophasic spiking. In conclusion, in the time sequence of induced epileptic activity, immediate shifts in DC-level EEG are plausible, followed by the spike activity-related widespread increase in spectral content. Morphological evolution does not appear to follow a clear continuum; rather, intermingled and variable spike or multispike waveforms generally lead to stabilised activity of high-amplitude monophasic spikes.

[Seizures in newborn infant]. / Vastasyntyneiden kohtausoireet.

Seizures in newborn infants are common. The may constitute a neurologic emergency or a nonepileptic, harmless symptom. Diagnostics is becoming more specific with current methodologies. Detailed description of seizures and their connection with EEG abnormalities are the diagnostic cornerstones. The treatment has made slow progress, but newer antiepileptic drugs may aid in the treatment of epileptic seizures in newborn infants in the future. For the time being, evidence-based research results for them are lacking, as well as data on long-term effects. Differential diagnosis of seizures has become increasingly important.

Automatic classification of penicillin-induced epileptic EEG spikes.

Penicillin-induced focal epilepsy is a well-known model in epilepsy research. In this model, epileptic activity is generated by delivering penicillin focally to the cortex. The drug induces interictal electroencephalographic (EEG) spikes which evolve in time and may later change to ictal discharges. This paper proposes a method for automatic classification of these interictal epileptic spikes using iterative K-means clustering. The method is shown to be able to detect different spike waveforms and describe their characteristic occurrence in time during penicillin-induced focal epilepsy. The study offers potential for future research by providing a method to objectively and quantitatively analyze the time sequence of interictal epileptic activity.

Coherence in depth electrodes during induction of deep anesthesia.

Our aim was to explore time-varying coherence values versus spacing and referencing of electrode contacts in thalamic level from human encephalographic (EEG) data. Data has been acquired during induction of propofol anesthesia until burst-suppression level in scalp EEG. Results are shown from coherence analysis applied to EEG signals from selected depth electrode contacts pair-wise of three subjects. Alpha coherence is the most prominent behavior in all channel pairs. It is persistent throughout the time period followed and in coherence calculated between bipolar derivations in depth electrodes.

Entropy of the EEG in transition to burst suppression in deep anesthesia: Surrogate analysis.

In this paper 5 methods for the assessment of signal entropy are compared in their capability to follow the changes in the EEG signal during transition from continuous EEG to burst suppression in deep anesthesia. To study the sensitivity of the measures to phase information in the signal, phase randomization as well as amplitude adjusted surrogates are also analyzed. We show that the selection of algorithm parameters and the use of normalization are important issues in interpretation and comparison of the results. We also show that permutation entropy is the most sensitive to phase information among the studied measures and that the EEG signal during high amplitude delta activity in deep anesthesia is of highly nonlinear nature.

EEG sources of noise in intraoperative somatosensory evoked potential monitoring during propofol anesthesia.

OBJECTIVE: It was hypothesized that somato- sensory evoked potentials can be achieved faster by selective averaging during periods of low spontaneous electroen- cephalographic (EEG) activity. We analyzed the components of EEG that decrease the signal-to-noise ratio of somatosensory evoked potential (SEP) recordings during propofol anesthesia. METHODS: Patient EEGs were recorded with a high sampling frequency during deep anesthesia, when EEGs were in burst suppression. EEGs were segmented visually into bursts, spindles, suppressions, and artifacts. Tibial somatosensory evoked potentials (tSEPs) were averaged offline separately for burst, suppression, and spindle segments using a signal bandwidth of 30-200 Hz. Averages achieved with 2, 4, 8, 16, 64, 128, and 256 responses were compared both visually, and by calculating the signal-to-noise ratios. RESULTS: During bursts and spindles, the noise levels were similar and significantly higher than during suppressions. Four to eight times more responses had to be averaged during bursts and spindles than during suppressions in order to achieve a similar response quality. Averaging selectively during suppressions can therefore yield reliable tSEPs in approximately one-fifth of the time required during bursts. CONCLUSION: The major source of EEG noise in tSEP recordings is the mixed frequency activity of the slow waves of bursts that occur during propofol anesthesia. Spindles also have frequency components that increase noise levels, but these are less important, as the number of spindles is fewer. The fastest way to obtain reliable tSEPs is by averaging selectively during suppressions.

Using the nonlinear control of anaesthesia-induced hypersensitivity of EEG at burst suppression level to test the effects of radiofrequency radiation on brain function.

BACKGROUND: In this study, investigating the effects of mobile phone radiation on test animals, eleven pigs were anaesthetised to the level where burst-suppression pattern appears in the electroencephalogram (EEG). At this level of anaesthesia both human subjects and animals show high sensitivity to external stimuli which produce EEG bursts during suppression. The burst-suppression phenomenon represents a nonlinear control system, where low-amplitude EEG abruptly switches to very high amplitude bursts. This switching can be triggered by very minor stimuli and the phenomenon has been described as hypersensitivity. To test if also radio frequency (RF) stimulation can trigger this nonlinear control, the animals were exposed to pulse modulated signal of a GSM mobile phone at 890 MHz. In the first phase of the experiment electromagnetic field (EMF) stimulation was randomly switched on and off and the relation between EEG bursts and EMF stimulation onsets and endpoints were studied. In the second phase a continuous RF stimulation at 31 W/kg was applied for 10 minutes. The ECG, the EEG, and the subcutaneous temperature were recorded. RESULTS: No correlation between the exposure and the EEG burst occurrences was observed in phase I measurements. No significant changes were observed in the EEG activity of the pigs during phase II measurements although several EEG signal analysis methods were applied. The temperature measured subcutaneously from the pigs' head increased by 1.6 degrees C and the heart rate by 14.2 bpm on the average during the 10 min exposure periods. CONCLUSION: The hypothesis that RF radiation would produce sensory stimulation of somatosensory, auditory or visual system or directly affect the brain so as to produce EEG bursts during suppression was not confirmed.

Vibration-induced white finger syndrome and carpal tunnel syndrome among Finnish metal workers.

OBJECTIVE: Officially 10-26 cases of vibration-induced white fingers (VWF) have been reported annually in Finland. It has been suggested that the numbers are underestimated. The purpose of the present study was to estimate the cumulative exposure to hand-arm vibration (HAV) and the prevalence of clinically diagnosed cases of VWF and carpal tunnel syndrome (CTS) in a population of Finnish metal workers and to determine the symptoms and clinical tests that would best predict the diagnosis. METHODS: A questionnaire on vibration exposure at the workplace and symptoms of the upper extremities was sent to a sample (n = 530) of members of the local Metalworkers Union. Those who reported finger blanching, numbness or tingling of the fingers or symptoms of CTS were invited to take part in clinical examinations. Their cumulative lifelong exposure to HAV was evaluated. Those whose symptoms referred to VWF or CTS were given a cold provocation test with the measurement of finger systolic blood pressure and electroneuromyography of the upper arms. RESULTS: Altogether 285 metal workers (54%) responded to the questionnaire, and 24 new cases of VWF (8.4%) and 12 cases of CTS (4.2%) were diagnosed. In the group of VWF patients, seven workers had both VWF and CTS. All of the workers diagnosed as having VWF also had numbness or tingling in their fingers. Consequently, questions concerning numbness and tingling, a two-point discrimination test, Phalen's test, and Tinell's test had a high predicting value for VWF. The exposure time of the VWF cases did not differ significantly from that of the study group as whole, but the cumulative exposure index was significantly higher. CONCLUSION: The results suggest that VWF is underdiagnosed in Finland. In screening for the health effects of HAV, sensorineural symptoms of hands should be carefully inquired about and examined in patients complaining of white fingers. More education on the recognition and evaluation of HAV exposure and its health effects is needed.

Tracking rhythm in long-term EEG recordings using empirical mode calculation.

A novel algorithm for the detection and tracking of rhythmic patterns in the EEG signal is presented. The algorithm includes the following steps: 1) linear filtering using symmetric impulse response, 2) calculation of the first intrinsic mode of the filter output and 3) calculation of instantaneous frequency and amplitude using the Hilbert transform. The linear filter is adapted according to the instantaneous frequency. The algorithm is shown to perform well in tracking the alpha rhythm (the alpha coma pattern) in critically ill patients sedated with midazolam.