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ObjectiveTo evaluate the use of interictal high-frequency oscillations (HFOs) in epilepsy surgery for prediction of postsurgical seizure outcome in a prospective multicenter trial.MethodsWe hypothesized that a seizure-free outcome could be expected in patients in whom the surgical planning included the majority of HFO-generating brain tissue while a poor seizure outcome could be expected in patients in whom only a few such areas were planned to be resected. Fifty-two patients were included from 3 tertiary epilepsy centers during a 1-year period. Ripples (80–250 Hz) and fast ripples (250–500 Hz) were automatically detected during slow-wave sleep with chronic intracranial EEG in 2 centers and acute intraoperative electrocorticography in 1 patient.ResultsThere was a correlation between the removal of HFO-generating regions and seizure-free outcome at the group level for all patients. No correlation was found, however, for the center-specific analysis, and an individual prognostication of seizure outcome was true in only 36 patients (67%). Moreover, some patients became seizure-free without removal of the majority of HFO-generating tissue. The investigation of influencing factors, including comparisons of visual and automatic analysis, using a threshold analysis for areas with high HFO activity, and excluding contacts bordering the resection, did not result in improved prognostication.ConclusionsOn an individual patient level, a prediction of outcome was not possible in all patients. This may be due to the analysis techniques used. Alternatively, HFOs may be less specific for epileptic tissue than earlier studies have indicated.
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Chen, Zhuying, Matias I. Maturana, Anthony N. Burkitt, Mark J. Cook, and David B. Grayden. "High-Frequency Oscillations in Epilepsy." Neurology 96, no. 9 (January 6, 2021): 439–48. http://dx.doi.org/10.1212/wnl.0000000000011465.
For the past 2 decades, high-frequency oscillations (HFOs) have been enthusiastically studied by the epilepsy community. Emerging evidence shows that HFOs harbor great promise to delineate epileptogenic brain areas and possibly predict the likelihood of seizures. Investigations into HFOs in clinical epilepsy have advanced from small retrospective studies relying on visual identification and correlation analysis to larger prospective assessments using automatic detection and prediction strategies. Although most studies have yielded promising results, some have revealed significant obstacles to clinical application of HFOs, thus raising debate about the reliability and practicality of HFOs as clinical biomarkers. In this review, we give an overview of the current state of HFO research and pinpoint the conceptual and methodological issues that have hampered HFO translation. We highlight recent insights gained from long-term data, high-density recordings, and multicenter collaborations and discuss the open questions that need to be addressed in future research.
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Matsumoto, Andrew, Benjamin H. Brinkmann, S. Matthew Stead, Joseph Matsumoto, Michal T. Kucewicz, W. Richard Marsh, Frederic Meyer, and Gregory Worrell. "Pathological and physiological high-frequency oscillations in focal human epilepsy." Journal of Neurophysiology 110, no. 8 (October 15, 2013): 1958–64. http://dx.doi.org/10.1152/jn.00341.2013.
High-frequency oscillations (HFO; gamma: 40–100 Hz, ripples: 100–200 Hz, and fast ripples: 250–500 Hz) have been widely studied in health and disease. These phenomena may serve as biomarkers for epileptic brain; however, a means of differentiating between pathological and normal physiological HFO is essential. We categorized task-induced physiological HFO during periods of HFO induced by a visual or motor task by measuring frequency, duration, and spectral amplitude of each event in single trial time-frequency spectra and compared them to pathological HFO similarly measured. Pathological HFO had higher mean spectral amplitude, longer mean duration, and lower mean frequency than physiological-induced HFO. In individual patients, support vector machine analysis correctly classified pathological HFO with sensitivities ranging from 70–98% and specificities >90% in all but one patient. In this patient, infrequent high-amplitude HFO were observed in the motor cortex just before movement onset in the motor task. This finding raises the possibility that in epileptic brain physiological-induced gamma can assume higher spectral amplitudes similar to those seen in pathologic HFO. This method if automated and validated could provide a step towards differentiating physiological HFO from pathological HFO and improving localization of epileptogenic brain.
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DeWeese, E. L., T. Y. Sullivan, and P. L. Yu. "Ventilatory response to high-frequency airway oscillation in humans." Journal of Applied Physiology 58, no. 4 (April 1, 1985): 1099–106. http://dx.doi.org/10.1152/jappl.1985.58.4.1099.
To investigate respiratory control during high-frequency oscillation (HFO), ventilation was monitored in conscious humans by respiratory inductive plethysmography during application at the mouth of high-frequency pressure oscillations. Studies were conducted before and after airway and pharyngeal anesthesia. During HFO, breathing became slow and deep with an increase in tidal volume (VT) of 37% (P less than 0.01) and inspiratory duration (TI) of 34% (P less than 0.01). Timing ratio (TI/TT) increased 14% (P less than 0.05) and respiratory frequency (f) decreased 12% (P less than 0.01). Mean inspiratory flow (VT/TI) did not change during HFO. Following airway anesthesia, VT increased only 26% during HFO (P less than 0.01), whereas significant changes in TI, TI/TT, and f were not observed. Pharyngeal anesthesia failed to diminish the effect of HFO on TI, TT, or f, although the increase in VT was reduced. These results indicate that 1) HFO presented in this manner alters inspiratory timing without affecting the level of inspiratory activity, and 2) receptors in the larynx and/or lower airways may in part mediate the response.
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Freitag, L., W. M. Long, C. S. Kim, and A. Wanner. "Removal of excessive bronchial secretions by asymmetric high-frequency oscillations." Journal of Applied Physiology 67, no. 2 (August 1, 1989): 614–19. http://dx.doi.org/10.1152/jappl.1989.67.2.614.
The present study evaluated whether high-frequency oscillations (HFO) with biased flow profiles applied at the airway opening are capable of altering mucus clearance. In eight anesthetized sheep, artificial mucus (100 P) was infused continuously (1 ml/min) into the left main bronchus via a cannula inserted through the dorsal wall of the left main bronchus after thoracotomy. Outcoming mucus was collected every 10 min from the end of a cuffed orotracheal tube. Animals were ventilated with a Harvard respirator at a low frequency with superimposed HFO at 14 Hz with asymmetrical waveforms generated by a digitally controlled electromagnetic piston pump (expiratory bias: peak expiratory flow 3.8 l/s, peak inspiratory flow 1.3 l/s; inspiratory bias: reverse of expiratory bias). The influence of posture and of HFO airflow bias on mucus clearance was determined. In the horizontal position, mucus clearance with expiratory biased HFO was 3.5 +/- 2 (SD) ml/10 min. Head-down tilt produced a clearance of 3.1 +/- 3 ml/10 min; addition of HFO with expiratory bias increased clearance to 11.0 +/- 2.0 ml/10 min (P less than 0.05). No clearance occurred with inspiratory biased HFO during head-down tilt. These results indicate that expiratory biased HFO at the airway opening can clear excessive airway secretions and augment clearance by postural drainage.
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Pearce, Allison, Drausin Wulsin, Justin A. Blanco, Abba Krieger, Brian Litt, and William C. Stacey. "Temporal changes of neocortical high-frequency oscillations in epilepsy." Journal of Neurophysiology 110, no. 5 (September 1, 2013): 1167–79. http://dx.doi.org/10.1152/jn.01009.2012.
High-frequency (100–500 Hz) oscillations (HFOs) recorded from intracranial electrodes are a potential biomarker for epileptogenic brain. HFOs are commonly categorized as ripples (100–250 Hz) or fast ripples (250–500 Hz), and a third class of mixed frequency events has also been identified. We hypothesize that temporal changes in HFOs may identify periods of increased the likelihood of seizure onset. HFOs (86,151) from five patients with neocortical epilepsy implanted with hybrid (micro + macro) intracranial electrodes were detected using a previously validated automated algorithm run over all channels of each patient's entire recording. HFOs were characterized by extracting quantitative morphologic features and divided into four time epochs (interictal, preictal, ictal, and postictal) and three HFO clusters (ripples, fast ripples, and mixed events). We used supervised classification and nonparametric statistical tests to explore quantitative changes in HFO features before, during, and after seizures. We also analyzed temporal changes in the rates and proportions of events from each HFO cluster during these periods. We observed patient-specific changes in HFO morphology linked to fluctuation in the relative rates of ripples, fast ripples, and mixed frequency events. These changes in relative rate occurred in pre- and postictal periods up to thirty min before and after seizures. We also found evidence that the distribution of HFOs during these different time periods varied greatly between individual patients. These results suggest that temporal analysis of HFO features has potential for designing custom seizure prediction algorithms and for exploring the relationship between HFOs and seizure generation.
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Ward, H. E., J. Armengol, and R. L. Jones. "Ventilation by external high-frequency oscillation in cats." Journal of Applied Physiology 58, no. 4 (April 1, 1985): 1390–99. http://dx.doi.org/10.1152/jappl.1985.58.4.1390.
Eight anesthetized tracheostomized cats were placed in an 8.2-liter airtight chamber with the trachea connected to the exterior. Thirty-two combinations of high-frequency oscillations (HFO) (0.5–30 Hz; 25–100 ml) were delivered for 10 min each in random order into the chamber. Arterial blood gas tensions during oscillation were compared with control measurements made after 10 min of spontaneous breathing without oscillation when the mean arterial PCO2 (PaCO2) was 30.1 Torr. Ventilation due to spontaneous breathing (Vs) and oscillation (Vo) were derived from the chamber pressure trace and a pneumotachograph, respectively. As the oscillation frequency increased, oscillated tidal volume (Vo) decreased from a mean of 39 (0.5 Hz) to 3.3 ml (30 Hz) when 100 ml was delivered to the chamber. From 6–25 Hz, apnea occurred with Vo less than estimated respiratory dead space (VD); the minimum effective Vo/VD ratio was 0.37 +/- 0.05. Although Vo was maximal at 10 Hz at each oscillation volume, the lowest PaCO2 occurred at 2–6 Hz, and arterial PO2 rose as expected during hypocapnia. Above 10 Hz, PaCO2 was determined by Vo and was independent of frequency, whereas at lower frequencies, PaCO2 was related to Vo; below 6 Hz, PaCO2 varied inversely with the calculated alveolar ventilation. As oscillations became more effective, both PaCO2 and Vs fell progressively and were highly correlated; apnea occurred when PaCO2 was reduced by a mean of 4.5 Torr. Mean chamber pressure remained near zero up to 15 Hz, indicating functional residual capacity did not change. We conclude that externally applied HFO can readily maintain gas exchange in vivo, with Vo less than VD at frequencies over 2 Hz.
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Mochizuki, Hitoshi, and Yoshikazu Ugawa. "High-Frequency Oscillations in Somatosensory System." Clinical EEG and Neuroscience 36, no. 4 (October 2005): 278–84. http://dx.doi.org/10.1177/155005940503600407.
The recent revival of interest in high-frequency oscillation (HFO) is triggered by getting an opportunity to noninvasively monitor the timing of highly synchronized and rapidly repeating population spikes generated in the human somatosensory system. HFOs could be recorded from brainstem, cuneothalamic relay neurons, thalamus, thalamocortical radiation, thalamocortical terminals and cortex with deep brain or surface electrodes, or with magnetoencephalography. Here we briefly review the HFOs at each level of somatosensory pathways. HFOs recorded at brainstem might be produced by volume conduction from oscillations of the medial lemniscus. Thalamic HFOs at around 1000 Hz frequency would be generated within the somatosensory thalamus. Cortical HFOs would be generated by at least a few different mechanisms, thalamocortical projection terminals, interneurons and pyramidal cells of the primary sensory cortex. HFOs have been studied in several ways: their modulation by arousal changes, movements or drugs, their recovery function, effects of transcranial magnetic stimulation on them and also their changes in patients with various neurological diseases.
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Plenz, D., and S. T. Kitai. "Generation of high-frequency oscillations in local circuits of rat somatosensory cortex cultures." Journal of Neurophysiology 76, no. 6 (December 1, 1996): 4180–84. http://dx.doi.org/10.1152/jn.1996.76.6.4180.
1. Rhythmic cortical activity was investigated with intracellular recordings in cortex-striatum-mesencephalon organotypic cultures grown for 42 +/- 3 (SE) days in vitro. 2. Electrical stimulation of supragranular layers induced a self-sustained high-frequency oscillation (HFO) in pyramidal neurons and interneurons. 3. The HFO started 197 +/- 39 ms after stimulation and had a mean duration of 1.0 +/- 0.2 s and an initial frequency of 38 +/- 2 Hz. A decrease in frequency at a rate of 11.5 +/- 2.7 Hz/s started on average 547 +/- 109 ms after the onset of the HFO. 4. During the HFO, local interneurons and pyramidal neurons synchronized their activities. The synaptic origin of the HFO was confirmed by its reversal potential at -57 +/- 4 mV. 5. These results suggest that a self-maintained HFO can be induced in local cortical circuits by excitation of supragranular layers. This HFO would facilitate synchronization between distant cortical and thalamic regions.
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Spampanato, Jay, and Istvan Mody. "Spike Timing of Lacunosom-Moleculare Targeting Interneurons and CA3 Pyramidal Cells During High-Frequency Network Oscillations In Vitro." Journal of Neurophysiology 98, no. 1 (July 2007): 96–104. http://dx.doi.org/10.1152/jn.00188.2007.
Network activity in the 200- to 600-Hz range termed high-frequency oscillations (HFOs) has been detected in epileptic tissue from both humans and rodents and may underlie the mechanism of epileptogenesis in experimental rodent models. Slower network oscillations including theta and gamma oscillations as well as ripples are generated by the complex spike timing and interactions between interneurons and pyramidal cells of the hippocampus. We determined the activity of CA3 pyramidal cells, stratum oriens lacunosum-moleculare (O-LM) and s. radiatum lacunosum-moleculare (R-LM) interneurons during HFO in the in vitro low-Mg2+ model of epileptiform activity in GIN mice. In these animals, interneurons can be identified prior to cell-attached recordings by the expression of green-fluorescent protein (GFP). Simultaneous local field potential recordings from s. pyramidale and on-cell recordings of individual interneurons and principal cells revealed three primary firing behaviors of the active cells: 36% of O-LM interneurons and 60% of pyramidal cells fired action potentials at high frequencies during the HFO. R-LM interneurons were biphasic in that they fired at high frequency at the beginning of the HFO but stopped firing before its end. When considering only the highest frequency component of the oscillations most pyramidal cells fired on the rising phase of the oscillation. These data provide evidence for functional distinction during HFOs within otherwise homogeneous groups of O-LM interneurons and pyramidal cells.
Dissertations / Theses on the topic "High Frequency Oscillations (HFO)":
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Zachrisson, Love. "HIGH-FREQUENCY OSCILLATIONS IN A MOUSE MODEL OF PARKINSON’S DISEASE." Thesis, Umeå universitet, Institutionen för psykologi, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-172265.
Dopamine replacement therapy is the main method of treating Parkinson’s Disease (PD), however over time this treatment causes increasingly abnormal, involuntary movements. This symptom, known as Levodopa-Induced-Dyskinesia (LID) is associated with aberrant, high frequency oscillations (HFOs) in the motor cortex and basal ganglia, as demonstrated with implanted electrodes in human Parkinson’s patients as well as in a rat model of Parkinson’s Disease. However, despite efforts to determine if the same high frequency oscillations are also present during dyskinesia in the widespread 6-OHDA mouse model of Parkinson’s Disease, studies have been unable to do so. By building and implanting a 64-channel multi-electrode array into a unilateral 6-OHDA lesioned mouse, we were able to record HFOs at 80Hz and >100Hz in the motor cortex, basal ganglia and thalamus in the lesioned hemisphere during LID. We also recorded bilateral HFOs at >100Hz in the intact hemisphere. With this work we show that the same HFOs that are present in the motor cortex and basal ganglia of rats and humans are also present in mice during dyskinesia. This work will act to further validate the 6-OHDA PD-model in mice and provide opportunities to investigate new treatments for Parkinson’s Disease, dyskinesia and other neurological conditions. It will also serve as a model to study a purposed mechanism underlying the information processing in populations of neurons. Dopaminbehandling är den mest förekommande metoden för att behandla Parkinsons sjukdom men detta orsakar dessvärre en bieffekt i form av gradvis förvärrande ofrivilliga rörelser. Detta beteendemönster kallas för Levodopa-Inducerad-Dyskinesi (LID) och med hjälp av elektrodimplantat i hjärnan, på parkinsonpatienter och djurmodeller av parkinsons, har man kunnat se att beteendet är förknippat med högfrekventa oscilleringar (HFO) av hjärnaktivitet i motorcortex och basala ganglierna. Trots försök att kartlägga om dessa högfrekventa oscilleringar också är närvarande i den populära 6-OHDA musmodellen av Parkinsons sjukdom, så har man hittills inte lyckats demonstrera detta. Genom att bygga och implantera ett elektrodimplantat med 64 kanaler i en ensidigt-leisonerad 6-OHDA musmodell av Parkinsons sjukdom så kunde vi åskådliggöra HFO i motor cortex, basala ganglierna och thalamus i den lesionerade hjärnhalvan under LID. Vi kunde också påvisa HFO som sträckte sig över till den intakta hjärnhalvan, med frekvenser över 100 Hz. Denna forskning ger stöd att 6-OHDA modellen för Parkinsons i möss är valid och ger möjlighet till nya metoder att utforska och behandla Parkinsons, dyskinesi och andra neurologiska åkommor. Studien lägger också grunden för framtida studier som ämnar att undersöka föreslagna mekanismer bakom sättet populationer av neuroner bearbetar information. ingår i ett projekt finansierat av Vetenskapsrådet #2018-02717
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Sag, Yusuf Ugur [Verfasser], Julia [Akademischer Betreuer] Jacobs-LeVan, and Kerstin Alexandra [Akademischer Betreuer] Klotz. "High frequency oscillations (HFO) als Biomarker zur Prädiktion der Entstehung einer Epilepsie nach erstem unprovoziertem Anfall im Kindesalter." Freiburg : Universität, 2020. http://d-nb.info/1227839561/34.
Macíčková, Magda. "Klasifikace vysokofrekvenčních oscilací v intrakraniálním EEG." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2019. http://www.nusl.cz/ntk/nusl-401034.
This Master’s thesis deals with investigation of high-frequency oscillations in intracranial electroencephalography in patients with pharmacoresistant epilepsy. It describes individual types of oscillations with respect to their frequency definition, examines their physiological differences and occurrence. In addition to conventional high-frequency oscillations (up to about 600 Hz), it also focuses on oscillations with a frequency component above 1kHz. According to recent studies, these oscillations could have higherspecificity for the determination of pathological tissue in the epileptic brain. The data for this work was obtained by manual labeling and categorization of approximately 1500 sections of the stereoencephalographic record signals of patients undergoing surgical removal of the epileptic foci and subsequently monitored for success in the operation. Differences between individual groups of oscillations and resected or unresected tissues are investigated in this work by methods using calculations of entropy signals or cross frequency coupling. The most significant results were achieved for the classification group (FR + vFR) vs. uFR, methods frequency-amplitude coupling and sample entropy 1. When categorizing according to information about channel resection, the Shannon entropy is the most successful classification parameter.
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Alvarado-Rojas, Catalina. "Multilevel approach to high-frequency oscillations (HFOs) in human epileptic networks." Paris 6, 2013. http://www.theses.fr/2013PA066452.
L’épilepsie est une pathologie dynamique qui s’exprime par une activité anormale des réseaux neuronaux. La période entre crises est caractérisée par une excitabilité transitoire hypersynchrone : les décharges interictales et les oscillations haute-fréquence (HFOs >40Hz). Au cours de ma thèse, j’ai mené une approche multi-niveau pour mieux comprendre les mécanismes de génération des HFOs et leur relation temporelle avec les crises. La première étude a concerné l’exploration in vitro des corrélats cellulaires des HFOs (~200Hz) sur l’hippocampe humain épileptique. Deux mécanismes différents ont été observés au niveau cellulaire en soulignant leur hétérogénéité. Dans une deuxième étude en utilisant des microlectrodes intracrâniennes pendant l’évaluation pré-chirurgicale des patients, nous avons enregistré simultanément le LFP et l’activité multi-unitaire. Les décharges interictales étaient précédées par HFOs (40-120Hz) dans 50% des cas, tous les deux associées à une activité neuronale hétérogène. Une dernière étude a été mise en place pour investiguer la dynamique des HFOs en relation aux crises. A partir d’enregistrements intracrâniens de long-terme, nous avons étudié la modulation de gamma (40-140Hz) par les rythmes plus lents (theta/delta) avant le début de la crise. Nous avons mis en évidence une perturbation dans ce couplage plusieurs minutes avant les crises dans un nombre significatif de patients (13%). En conclusion, les HFOs pathologiques peuvent être générées par des mécanismes différents, sont associées à une activité cellulaire hétérogène, et sont modulés différemment pendant les périodes pré-critiques. Ainsi, leur étude est donc importante pour la compréhension des mécanismes de génération des crises Epilepsy is a dynamical disease reflecting abnormal activity of neuronal networks. The interictal period (between seizures), is characterized by transient hypersynchronous excitability emerging as interictal discharges and high frequency oscillations (HFOs >40Hz). During my thesis, a multi-level approach was performed, in order to investigate the mechanisms of HFO generation and their temporal relation with seizures. A first study consisted on the exploration of cellular correlates underlying HFOs (~200 Hz) in epileptic slices of human hippocampus. Two different cellular mechanisms were observed, highlighting the heterogeneity of underlying cellular behaviors. In a second study using intracranial microelectrodes during presurgical evaluation of patients, we recorded simultaneously LFP and multi-unit activity. Interictal discharges were preceded by HFOs (40-120Hz) in 50% of cases, both associated to heterogeneous neuronal firing. A final study was performed to investigate the dynamics of HFOs in relation to seizures. From long-term intracranial recordings, we studied the modulation of gamma (40-140Hz) by slower rhythms (theta/delta) before the seizure onset. We showed that a perturbation of this coupling occurs several minutes before the seizure onset for a significant number of patients (13%). We conclude that HFOs in epileptic networks can be generated by different mechanisms, are associated to a heterogeneous cellular firing, and are modulated in a different way during the preictal period. Hence, their study is important for a better understanding of the mechanisms of seizure generation
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Kuo, Chia-Hung. "THE ANALYSIS OF HIGH FREQUENCY OSCILLATIONS AND SUPPRESSION IN EPILEPTIC SEIZURE DATA." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1396411237.
Milon-Harnois, Gaëlle. "Détection automatique et analyse des oscillations à haute fréquence en EEG-HD de surface." Electronic Thesis or Diss., Angers, 2023. http://www.theses.fr/2023ANGE0054.
Un tiers des épileptiques ne voient pas d'amélioration avec les traitements actuels, poussant les médecins à envisager la chirurgie pour enlever la zone cérébrale générant les crises. Les Oscillations à Haute Fréquence (HFO) émergent comme biomarqueur pour localiser ces zones épileptogènes, mais leur détection est difficile en raison de leur rareté et de leur brièveté. En EEG de scalp la faible amplitude du signal complexifie la tâche. Cette thèse vise à automatiser la détection de HFO dans des signaux EEG-HD enregistrés à 1 KHz sur 256 électrodes chez 5 patients. Après marquage visuel des HFO, des modèles de classification entre HFO et bruit de fond ont été explorés. Les connaissances du traitement de signal ont été exploitées pour extraire des caractéristiques du domaine temporel ou fréquentiel. Les caractéristiques les plus pertinentes statistiquement ont été sélectionnées et soumises à des algorithmes supervisés classiques (Régression logistique, forêt aléatoire, MLP, gradient boosting). Ces méthodes ont été comparées à des algorithmes profonds (CNN, LSTM, Attention) générant automatiquement les caractéristiques du signal dans le domaine temporel 1D ou celles des cartes 2D temps fréquence. Tous les modèles montrent des résultats probants, les algorithmes profonds 1D étant plus efficaces avec une sensibilité de 91% et une spécificité de 87%, surpassant les détecteurs d’HFO de surface publiés. L’exécution des meilleurs modèles sur la totalité du signal pour détecter automatiquement les HFO a affiché des résultats prometteurs mais cette partie du travail reste à améliorer pour pallier la rareté des HFO dans les données. Plusieurs pistes de recherche sont proposées Conditions of a third of epileptics are not improved with current treatments, pushing doctors to consider surgery to remove the brain area generating seizures. High Frequency Oscillations (HFO) are emerging as a biomarker to localize these epileptogenic zones, but their detection is difficult due to their rarity and brevity. In scalp EEG the low amplitude of the signal complicates the task. This thesis aims to automate the detection of HFO in EEG-HD signals recorded at 1 KHz on 256 electrodes in 5 pediatric patients. After visual marking of HFO, classification models between HFO and background noise were explored. Signal processing knowledge has been exploited to extract features from time or frequency domain. The most statistically relevant features were selected and submitted to classic supervised algorithms (Logistic regression, random forest, MLP, gradient boosting). These methods were compared to deep algorithms (CNN, LSTM, Attention) automatically generating signal characteristics in the 1D time domain or those of 2D time-frequency maps. All models show convincing results, with the deep 1D algorithms being more efficient reaching 91% sensitivity and 87% specificity, outperforming previously published surface HFO detectors. Running the best models on the entire signal to automatically detect HFO showed promising results but this part of the work remains to be improved to overcome the HFO rarity in the data. Several lines of research are suggested
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Bougacha, Salma. "High frequency oscillations in bounded elastic media." Thesis, Evry-Val d'Essonne, 2010. http://www.theses.fr/2010EVRY0047/document.
Cette thèse est consacrée à l’étude haute fréquence de problèmes de Dirichlet et Neumann pour le système de l’élasticité. On y étudie le phénomène de réflexion au bord au moyen de deux techniques : la sommation de faisceaux gaussiens et les mesures de Wigner. Dans les chapitres 1 et 2, on commence par étudier le problème plus simple de l’équation des ondes scalaire à une vitesse. Sous certaines hypothèses sur les conditions initiales, on construit des solutions approchées par superposition de faisceaux gaussiens. La justification de l’asymptotique se fonde sur une estimation de normes de certains opérateurs intégraux à phases complexes. Pour des conditions initiales plus générales, on utilise les mesures de Wigner pour calculer la densité d’énergie microlocale. On calcule explicitement les transformées de Wigner d’intégrales de faisceaux gaussiens. Le comportement de la densité d’énergie microlocale de la solution exacte se déduit de celui établi pour la solution approchée. Dans le chapitre 3, on utilise les résultats établis pour les sommes infinies de faisceaux gaussiens pour construire une solution approchée pour les équations de l’élasticité et calculer sa densité d’énergie microlocale. L’existence de deux vitesses différentes dans le système de l’élasticité introduit de nouvelles difficultés qui sont traitées dans ce chapitre This thesis is devoted to the study of the high frequency Dirichlet and Neumann problems for the elasticity system. We study the reflection phenomenon at the boundary by means of two techniques: Gaussian beams summation and Wigner measures. In chapters 1 and 2, we start by studying the simpler problem of the scalar wave equation with one speed. Under some hypotheses on the initial conditions, we build an approximate solution by a Gaussian beams superposition. Justification of the asymptotics is based on norms estimate of some integral operators with complex phases. For more general initial conditions, we use Wigner measures to compute the microlocal energy density. We compute Wigner transforms of Gaussian beams integrals in an explicit way. The behaviour of the microlocal energy density for the exact solution is deduced from the one for the approximate solution. In chapter 3, we use the established results on infinite sums of Gaussian beams to build an approximate solution for the elasticity equations and to compute its microlocal energy density. We treat new difficulties arising from the existence of two different speeds in the elasticity system
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Ljungberg, Stefan. "High Frequency Oscillations at an Electric Double Layer." Thesis, KTH, Rymd- och plasmafysik, 1995. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-91579.
Gaskell, J. "High-frequency oscillations in graphene resonant tunnelling heterostructures." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/33694/.
In this thesis, the form of the current-voltage characteristics and the resulting current oscillations in graphene-hexagonal boron nitride heterostructures are explored by means of theoretical investigation and are supported by experimental observations. The conditions for resonant tunnelling and the effect of device and circuit parameters are examined through simulation of the charge dynamics using the Bardeen Transfer Hamiltonian method. Studies of the effect of induced moir\'e patterns between the crystallographically aligned graphene and the boron nitride lattices are also undertaken, with recommendations for future investigation. It is theoretically shown that samples containing two layers of graphene, separated by hexagonal boron nitride tunnel barriers, produced higher frequency oscillations when the graphene lattices are aligned. This was found to be due to the decrease in wavefunction overlap in the misaligned samples, which is not compensated by the higher density of states available for tunnelling. Chemical doping of the graphene layers are also found to increase the frequency, as it allows the Dirac cones to be brought into alignment for resonant tunnelling with a higher number of states available. It is known that the mismatch in lattice constant between the graphene lattice and the hexagonal boron nitride lattice creates a moir\'e pattern. This, in turn, induces additional Dirac points in the band structure and thus leads to new features in the current-voltage characteristics. The theoretical simulations presented in this thesis are substantiated by recently-published experimental results, and provide insight into possible future high-frequency, room-temperature solid state oscillators and amplifiers. In conclusion, the mechanisms for resonant tunnelling in multiple graphene heterostructures are identified and demonstrated in this work, and provide promising evidence for novel high frequency technologies and further research.
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Westner, Britta [Verfasser]. "High frequency oscillations in healthy brain functions / Britta Westner." Konstanz : Bibliothek der Universität Konstanz, 2017. http://d-nb.info/1140736612/34.
Books on the topic "High Frequency Oscillations (HFO)":
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United States. National Aeronautics and Space Administration., ed. The detection and characterization of high frequency and high wavenumber solar oscillations. [Washington, DC: National Aeronautics and Space Administration, 1992.
Fernandes, David Neil. The detection and characterization of high frequency and high wavenumber solar oscillations. Springfield, Va: Available from the National Technical Information Service, 1992.
Cuartero, Mireia, and Niall D. Ferguson. High-frequency ventilation and oscillation. Oxford University Press, 2016. http://dx.doi.org/10.1093/med/9780199600830.003.0098.
High-frequency oscillatory ventilation (HFOV) is a key member of the family of modes called high-frequency ventilation and achieves adequate alveolar ventilation despite using very low tidal volumes, often below the dead space volume, at frequencies significantly above normal physiological values. It has been proposed as a potential protective ventilatory strategy, delivering minimal alveolar tidal stretch, while also providing continuous lung recruitment. HFOV has been successfully used in neonatal and paediatric intensive care units over the last 25 years. Since the late 1990s adults with acute respiratory distress syndrome have been treated using HFOV. In adults, several observational studies have shown improved oxygenation in patients with refractory hypoxaemia when HFOV was used as rescue therapy. Several small older trials had also suggested a mortality benefit with HFOV, but two recent randomized control trials in adults with ARDS have shed new light on this area. These trials not show benefit, and in one of them a suggestion of harm was seen with increased mortality for HFOV compared with protective conventional mechanical ventilation strategies (tidal volume target 6 mL/kg with higher positive end-expiratory pressure). While these findings do not necessarily apply to patients with severe hypoxaemia failing conventional ventilation, they increase uncertainty about the role of HFOV even in these patients.
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Simenson, Oscar. Chaffee Arc and High Frequency Oscillations. Creative Media Partners, LLC, 2018.
Gotman, Jean, and Nathan E. Crone. High-Frequency EEG Activity. Edited by Donald L. Schomer and Fernando H. Lopes da Silva. Oxford University Press, 2017. http://dx.doi.org/10.1093/med/9780190228484.003.0033.
Activities with frequencies between 60 and 80 Hz and approximately 500 Hz are labeled here as high-frequency activities. They were largely ignored until the beginning of the millennium, but their importance is now well recognized. They can be divided into activities occurring in the healthy brain in relation to sensory, motor, and cognitive or memory activity and activities occurring in the epileptic brain in the form of brief events (high-frequency oscillations), which appear to be an important marker of the brain regions that are able to generate seizures of focal origin. In humans, most of the work related to these activities has been done in intracerebral electrodes, where they are relatively frequent and easy to identify. They have been recorded in scalp electroencephalograms in some circumstances, however. This chapter reviews the recording methods, the circumstances in which they occur, their mechanism of generation, and their clinical significance.
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Sarnthein, Johannes, Julia Jacobs, and Maeike Zijlmans, eds. High-Frequency Oscillations in the Hippocampus as Biomarkers of Pathology and Healthy Brain Function. Frontiers Media SA, 2021. http://dx.doi.org/10.3389/978-2-88971-689-0.
Seeck, Margitta, and Donald L. Schomer. Intracranial EEG Monitoring. Edited by Donald L. Schomer and Fernando H. Lopes da Silva. Oxford University Press, 2017. http://dx.doi.org/10.1093/med/9780190228484.003.0029.
Intracranial electroencephalography (iEEG) is used to localize the focus of seizures and determine vital adjacent cortex before epilepsy surgery. The two most commonly used electrode types are subdural and depth electrodes. Foramen ovale electrodes are less often used. Combinations of electrode types are possible. The choice depends on the presumed focus site. Careful planning is needed before implantation, taking into account the results of noninvasive studies. While subdural recordings allow better mapping of functional cortex, depth electrodes can reach deep structures. There are no guidelines on how to read ictal intracranial EEG recordings, but a focal onset (<5 contacts) and a high-frequency onset herald a good prognosis. High-frequency oscillations have been described as a potential biomarker of the seizure onset zone. Intracranial recordings provide a focal but magnified view of the brain, which is also exemplified by the use of microelectrodes, which allow the recording of single-unit or multi-unit activity.
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Brandeis, Daniel, Sandra K. Loo, Grainne McLoughlin, Hartmut Heinrich, and Tobias Banaschewski. Neurophysiology. Oxford University Press, 2018. http://dx.doi.org/10.1093/med/9780198739258.003.0009.
Neurophysiology allows us to understand and modulate the neural mechanisms in ADHD with high time- and/or frequency-resolution. These non-invasive methods include electroencephalographic recordings at rest and during tasks, with spontaneous and event-related oscillations and potentials tracking covert processing and transcranial neuromodulation through magnetic or electric fields. The findings indicate consistent cognitive and neural deficits in ADHD related to impaired attention and deficient inhibition. Advanced signal processing and source imaging methods often converge with other imaging approaches. Neurophysiological findings also reveal considerable heterogeneity in ADHD regarding cognitive, affective, and genetic subtypes. This illustrates the importance of dimensional approaches and of pathophysiological mechanisms partly shared with other disorders. Although several potential neurophysiological markers of ADHD have been considered, a clinical use for individual diagnostics and classification is not supported to date. More research should clarify the clinical potential of multivariate multimodal classification and prediction of treatment outcome to advance individualized treatment.
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Mauguière, François, and Luis Garcia-Larrea. Somatosensory and Pain Evoked Potentials. Edited by Donald L. Schomer and Fernando H. Lopes da Silva. Oxford University Press, 2017. http://dx.doi.org/10.1093/med/9780190228484.003.0043.
This chapter discusses the use of somatosensory evoked potentials (SEPs) and pain evoked potentials for diagnostic purposes. The generators of SEPs following upper limb stimulation have been identified through intracranial recordings, permitting the analysis of somatosensory disorders caused by neurological diseases. Laser activation of fibers involved in thermal and pain sensation has extended the applications of evoked potentials to neuropathic pain disorders. Knowledge of the effects of motor programming, paired stimulations, and simultaneous stimulation of adjacent somatic territories has broadened SEP use in movement disorders. The recording of high-frequency cortical oscillations evoked by peripheral nerve stimulation gives access to the functioning of SI area neuronal circuitry. SEPs complement electro-neuro-myography in patients with neuropathies and radiculopathies, spinal cord and hemispheric lesions, and coma. Neuroimaging has overtaken SEPs in detecting and localizing central nervous system lesions, but SEPs still permit assessment of somatosensory and pain disorders that remain unexplained by anatomical investigations.
Book chapters on the topic "High Frequency Oscillations (HFO)":
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Harr, Jeffrey N., Philip F. Stahel, Phillip D. Levy, Antoine Vieillard-Baron, Yang Xue, Muhammad N. Iqbal, Jeffrey Chan, et al. "High-Frequency Oscillation (HFO)." In Encyclopedia of Intensive Care Medicine, 1114. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-00418-6_1700.
Sadek, Zayneb, Abir Hadriche, and Nawel Jmail. "Clustering of High Frequency Oscillations HFO in Epilepsy Using Pretrained Neural Networks." In Intelligent Systems Design and Applications, 100–107. Cham: Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-35501-1_10.
Rossi, A., T. E. Stewart, and V. M. Ranieri. "High Frequency Oscillation (HFO): Physiological Basis for a Potentially ‘Optimal’ Protective Ventilatory Strategy." In Intensive Care Medicine, 288–94. New York, NY: Springer New York, 2003. http://dx.doi.org/10.1007/978-1-4757-5548-0_28.
Guesmi, Thouraya, Abir Hadriche, and Nawel Jmail. "Effective Connectivity of High-Frequency Oscillations (HFOs) Using Different Source Localization Techniques." In Intelligent Systems Design and Applications, 377–84. Cham: Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-35507-3_36.
Guesmi, Thouraya, Abir Hadriche, Nawel Jmail, and Chokri Ben Amar. "Evaluation of Stationary Wavelet Transforms in Reconstruction of Pure High Frequency Oscillations (HFOs)." In Lecture Notes in Computer Science, 357–63. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-51517-1_32.
Joly, J. L., and J. Rauch. "High Frequency Similinear Oscillations." In Mathematical Sciences Research Institute Publications, 202–16. New York, NY: Springer US, 1987. http://dx.doi.org/10.1007/978-1-4613-9583-6_7.
Jefferies, Stuart M. "High-Frequency Solar Oscillations." In New Eyes to See Inside the Sun and Stars, 415–22. Dordrecht: Springer Netherlands, 1998. http://dx.doi.org/10.1007/978-94-011-4982-2_93.
Gues, Olivier. "Viscous Boundary Layers and High Frequency Oscillations." In Singularities and Oscillations, 61–77. New York, NY: Springer New York, 1997. http://dx.doi.org/10.1007/978-1-4612-1972-9_4.
Arévalo, M. J., J. E. Solheim, and C. Lázaro. "High frequency oscillations in SS CYGNI." In White Dwarfs, 462–64. Berlin, Heidelberg: Springer Berlin Heidelberg, 1989. http://dx.doi.org/10.1007/3-540-51031-1_369.
Watts, Anna L., and Tod E. Strohmayer. "High frequency oscillations during magnetar flares." In Isolated Neutron Stars: From the Surface to the Interior, 625–29. Dordrecht: Springer Netherlands, 2007. http://dx.doi.org/10.1007/978-1-4020-5998-8_87.
Conference papers on the topic "High Frequency Oscillations (HFO)":
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Adhikari, NK, ND Ferguson, S. Mehta, A. Freitag, JO Friedrich, JT Granton, Q. Zhou, TE Stewart, and MO Meade. "Current High Frequency Oscillation (HFO) Utilization in Ontario." In American Thoracic Society 2009 International Conference, May 15-20, 2009 • San Diego, California. American Thoracic Society, 2009. http://dx.doi.org/10.1164/ajrccm-conference.2009.179.1_meetingabstracts.a3072.
Hand, L., F. Lamontagne, N. Ferguson, A. Bashir, K. Czarnecka, D. Lichty, N. Adhikari, D. Cook, and M. Meade. "Changes in Respiratory Variables upon Initiation of High Frequency Oscillation (HFO)." In American Thoracic Society 2009 International Conference, May 15-20, 2009 • San Diego, California. American Thoracic Society, 2009. http://dx.doi.org/10.1164/ajrccm-conference.2009.179.1_meetingabstracts.a3821.
Chaibi, Sahbi, Chahira Mahjoub, Fatma Krikid, Ahmad Karfoul, Regine Le Bouquin Jeannes, and Abdennaceur Kachouri. "Pitfalls of spikes filtering for detecting High Frequency Oscillations (HFOs)." In 2021 18th International Multi-Conference on Systems, Signals & Devices (SSD). IEEE, 2021. http://dx.doi.org/10.1109/ssd52085.2021.9429411.
Macedo, D. R., G. M. Silva, A. P. Fortes, G. P. de Sa, J. V. Borges, M. Campos, T. S. Rodrigues, and J. B. Destro Filho. "High-frequency oscillations (HFOs) in electroencephalography: Review and case study." In 2013 ISSNIP Biosignals and Biorobotics Conference: Biosignals and Robotics for Better and Safer Living (BRC). IEEE, 2013. http://dx.doi.org/10.1109/brc.2013.6487546.
Spencer, Reed W., John A. Bomidi, and Xu Huang. "Drill Bit Design Features that Initiate and Reduce High Frequency Torsional Oscillations." In SPE/IADC International Drilling Conference and Exhibition. SPE, 2021. http://dx.doi.org/10.2118/204102-ms.
AbstractThis paper reports the development of and the results of high frequency torsional oscillation (HFTO) tests performed on full-sized PDC drill bits and single cutters in a drilling laboratory. The research team used a pressurized laboratory drilling rig to test different drill bit designs in new and worn conditions. These tests were performed in different rock types, at different revolution per minute (RPM), weight on bit (WOB) and depth of cut (DOC) values. High frequency drill stem torque (5120 Hz) and in-bit tangential acceleration (1400 Hz) data were recorded, along with all other drilling parameters. Spectrograms of torque data were plotted to identify frequency changes in time. The torque data was filtered to remove the low frequency behavior and focus on the HFTO behavior. The high frequency torque signal correlates well with in-bit tangential accelerations. Root mean square (RMS) values of this filtered torque signal were calculated and plotted vs average WOB, depth of cut, and torque values. Sharp and worn bit geometry, were dull graded on a per cutter basis and were input to a 3D drilling modeling software and correlated with test data in order to determine the DOC at which wear flats or cutting faces engage the rock and cause changes in HFTO behavior. The main results from this research are 1) a lab test and data analysis were developed that can measure a drill bit's propensity to initiate HFTO vibrations in the BHA, 2) HFTO RMS high-pass filtered torque values generally increase with DOC, 3) bits in the new state show more HFTO behavior if cutter design is more aggressive, and 4) wear flat engagement causes high HFTO behavior.
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Hohl, A., A. Kueck, V. Kulke, and K. Glowatzki. "The Nature of the Interaction Between Bit-Whirl and High-Frequency Torsional Oscillations." In International Petroleum Technology Conference. IPTC, 2024. http://dx.doi.org/10.2523/iptc-23989-ms.
Abstract High-Frequency Torsional Oscillations (HFTO) are bit induced self-excited vibrations which can cause downhole tool failures and reduce the reliability of downhole tools. It is essential to understand the interaction of HFTO with other vibrational phenomena to develop effective HFTO mitigation strategies. While coupling with axial vibrations and stick-slip have already been studied extensively, the interaction of HFTO with lateral vibrations has received less attention. This paper analyzes this interaction based on a bit rock interaction model that accounts for the superimposed movement of whirl and HFTO at the bit. The excitation of HFTO can be attributed to a velocity-dependent characteristic of the cutting torque. A model that incorporates the superposition of lateral and torsional movement at the bit is used to calculate the velocity-dependent bit torque based on three components: the cutting velocity at each cutter, the normal force distribution along bit blades, and velocity-dependent forces between the bit and the rock. The velocity distribution is based on a kinematic model that superimposes the lateral motion of whirling and the rotational motion of HFTO. The normal force distribution is derived from the bit blade and cutter configuration, and the velocity-dependent force characteristics at each bit element is based on findings of laboratory tests with single cutting elements. A continuous multivariable function determines the nonlinear drilling torque characteristic depending on the amplitudes of HFTO and backward whirl. Evaluation of the simulated drilling torque shows that HFTO cannot be excited in presence of bit backward whirl. Specifically, it was found that an increasing rate of bit backward whirl leads to a bit torque characteristic generating less energy input or even energy output to HFTO. This is caused by backwards cutters with negative cutting torques corresponding to high energy dissipation. Forward whirl, on the other hand, cannot suppress HFTO. Comparison with laboratory data confirms these results. Cutter geometry and normal force distribution do not appear to have a significant effect on the results in either case. The new bit model provides a physics-based explanation of why bit backward whirl and torsional vibrations cannot be observed simultaneously. The influence of parameters, like the cutting-edge geometry, can be evaluated much faster than, for example, with particle or finite element models.
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Armin, Kueck, Everhard Eliah, Huang Xu, Valbuena Franklin, Reckmann Hanno, and Bomidi John. "Qualifying Bit Influence on High-Frequency Torsional Oscillations Based on Full-Scale Laboratory Experiments." In SPE/IADC International Drilling Conference and Exhibition. SPE, 2023. http://dx.doi.org/10.2118/212566-ms.
Abstract High-Frequency-Torsional Oscillations (HFTO) generate dynamic loads that can damage drilling tools, resulting in, for example cracks, twist-offs or broken electronics. They are triggered by the interaction of bits and rocks and force operators to reduce rotary spped (RPM) and weight on bit (WOB) losing drilling performance in the process. Recently, a full-scale drilling test rig was proven to generate verified HFTO behavior under laboratory conditions (Everhard et. al. 2023). This rig allows for a comprehensive study of the influences of bit characteristics on HFTO for the first time. This paper presents methods to qualify bit features to suppress HFTO. Effective HFTO influencing properties are identified and discussed. The full-scale laboratory test rig drills rocks in a pressurized rock chamber. ROP, WOB, RPM, pressure, bit type and rock type can be varied. High-frequency measurement instrumentation, including new in-bit sensing, record the tangential accelerations and dynamic torque at various positions in the laboratory rig. The type of excited torsional vibrations match vibrations in the field indicating that learnings in the lab translate to the field. To study the influence of bit and operating parameters on HFTO, PDC-bits of varying design are used to drill rocks under varying pressures, RPMs and WOB. The data are used to develop evaluation methods to rank bit-rock combinations with regards to the stability and severity of the generated vibrations. Stability maps relating RPM, WOB, and vibration proved to be a good measure to reliably identify HFTO and rank bit-rock combinations and applied operating parameters, by their susceptibility to HFTO. Bit properties, such as cutter shape, cutter placement or rock type control the energy intake per vibration cycle and, hence, the excitation of torsional vibrations. The operating parameter space indicating stable drilling states can be maximized by properly choosing bit features. Rock types triggering HFTO are identified using segmented core tests. When HFTO is present and fully developed, the severity of vibrations scales with the angular velocity of the bit (RPM) but not with the WOB. If HFTO is absent, WOB and RPM act as an "on-off" switch to HFTO. The threshold of WOB and RPM triggering HFTO is established for bit-rock combinations. The stable operating zone can be influenced by adding damping devices to the BHA. The findings also result in recommendations for operating BHAs in the field. Studying HFTO in a full-scale laboratory environment using the presented methods enables the development of robust and reliable HFTO countermeasures. Major influences on HFTO are identified and scientifically proven; understanding these characteristics will result in HFTO suppressing bits and tools. Ultimately, HFTO mitigation allows drilling engineers to optimize drilling parameters and reduce drilling time while simultaneously decreasing tool-failure probability and associated NPT and costs.
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Simozo, Fabrício Henrique, João Batista Destro Filho, and Luiz Otávio Murta Junior. "Detrended-Fluctuation-Analysis (DFA) and High-Frequency-Oscillation (HFO) Coefficients and Their Relationship to Epileptic Seizures." In International Congress on Neurotechnology, Electronics and Informatics. SCITEPRESS - Science and and Technology Publications, 2014. http://dx.doi.org/10.5220/0005095000990105.
Wilson, J. K., G. Heisig, and C. Freyer. "HFTO Solved: Proven Mitigation of High Frequency Torsional Oscillations in Motor-Assisted Rotary Steerable Applications." In IADC/SPE International Drilling Conference and Exhibition. SPE, 2022. http://dx.doi.org/10.2118/208739-ms.
Abstract High frequency torsional oscillation (HFTO) has gained considerable attention over the past several years due, in large part, to the continued use of motor-assisted Rotary-Steerable Systems. The consequences of such vibration events can be increased repair and maintenance costs, noisy measurements, and/or premature failures. While there are commercial tools available that can provide some relief to the symptoms of HFTO, data gathered thus far does not point to a consistent, reliable, and cost-effective solution to the problem. In light of current HFTO mitigation limitations, a new solution has been developed that shows promise in limiting the HFTO response in the BHA, if not removing it entirely. This new mitigation component is integrated directly into a Rotary-Steerable System. As a result, there are no requirements for additional tooling, connections, or special handling to mitigate these vibrations. The development of the presented method for mitigating HFTO stems from several years of gathering, and thoroughly analyzing, downhole data captured in a rotary-steerable system run below mud motors. A method for detecting HFTO in real-time is also presented, and the frequency and vibrational pattern of this dynamic phenomenon is confirmed in post-well reviews of high frequency data. Proprietary modeling is used to confirm that the measured frequencies seen downhole are associated with torsional resonant frequencies of the BHA, which is a defining characteristic of this particular vibration mode. A concept is developed for mitigating these types of downhole vibrations, based on the detailed understanding of the vibration characteristics, using a proven approach from outside the industry. Feasibility of this technology is confirmed through extensive vibration modeling. Prototype tools have been built and tested downhole in several US land basins over the past year. The positive results seen during initial field-testing has led to the new HFTO mitigation tool now being a standard technology for motor-assist RSS applications. Results have shown a consistent reduction in HFTO vibration, both in terms of amplitude and duration. Amplitude reductions between 50-100% have been observed routinely, which has led to a measureable increase in reliability and longevity of components being run below a mud motor. Based on how the mitigation tool is set up, a greater or lesser damping effect is seen in the measured HFTO response. This suggests the mitigation tool can be adjusted for targeted damping in certain scenarios, and may have a benefit in more than just rotary-steerable applications.
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Manilal, P. I., and A. M. Al-Jumaily. "Interaction of Neonates With a Bubble Oscillation System." In ASME 2005 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/detc2005-84331.
The aim of this research is to predict the interaction of neonates suffering from Respiratory Distress Syndrome (RDS) with high frequency pressure oscillations (HFPO) such as those produced by a bubble oscillation (BO) system. Many different postulations exist as to why pressure oscillations enhance respiratory performance; however, the scope of this work focuses on the speculation that the vibrations produced by the pressure oscillations cause the neonatal airway walls to resonate at their natural frequencies, thereby helping to relax the respiratory walls and give the neonate a better chance of recovery.
Reports on the topic "High Frequency Oscillations (HFO)":
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Lyo, Sungkwun Kenneth, Wei Pan, John Louis Reno, Joel Robert Wendt, and Daniel Lee Barton. LDRD final report on Bloch Oscillations in two-dimensional nanostructure arrays for high frequency applications. Office of Scientific and Technical Information (OSTI), September 2008. http://dx.doi.org/10.2172/948689.
