190 results on '"MENDEZ, MARTIN"'
Search Results
152. Detection of obstructive sleep apnea in children using decreases in the amplitude fluctuations of PPG signal and HRV
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Gil, Eduardo, primary, Mendez, Martin, additional, Vergara, Jose Maria, additional, Cerutti, Sergio, additional, Bianchi, Anna Maria, additional, and Laguna, Pablo, additional
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- 2008
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153. Detection of Sleep Apnea from surface ECG based on features extracted by an Autoregressive Model
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Mendez, Martin O., primary, Ruini, Davide D., additional, Villantieri, Omar P., additional, Matteucci, Matteo, additional, Penzel, Thomas, additional, Cerutti, Sergio, additional, and Bianchi, Anna M., additional
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- 2007
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154. Sleep Monitoring Through a Textile Recording System
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Devot, Sandrine, primary, Bianchi, Anna M., additional, Naujoka, Elke, additional, Mendez, Martin O., additional, Braurs, Andreas, additional, and Cerutti, Sergio, additional
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- 2007
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155. Conservation genetics of the franciscana dolphin in Northern Argentina: population structure, by-catch impacts, and management implications
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Mendez, Martin, primary, Rosenbaum, H. C., additional, and Bordino, P., additional
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- 2007
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156. Signal Processing and Feature Extraction for Sleep Evaluation in Wearable Devices
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Bianchi, Anna M., primary, Villantieri, Omar P., additional, Mendez, Martin O., additional, and Cerutti, Sergio, additional
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- 2006
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157. Mesh-based approach for the 3D analysis of anatomical structures of interest in Radiotherapy.
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Mejia-Rodriguez, Aldo R., Scalco, Elisa, Tresoldi, Daniele, Bianchi, Anna M., Arce-Santana, Edgar R., Mendez, Martin O., and Rizzo, Giovanna
- Abstract
In this paper a method based on mesh surfaces approximations for the 3D analysis of anatomical structures in Radiotherapy (RT) is presented. Parotid glands meshes constructed from Megavoltage CT (MVCT) images were studied in terms of volume, distance between center of mass (distCOM) of the right and left parotids, dice similarity coefficient (DICE), maximum distance between meshes (DMax) and the average symmetric distance (ASD). A comparison with the standard binary images approach was performed. While absence of significant differences in terms of volume, DistCOM and DICE indices suggests that both approaches are comparable, the fact that the ASD showed significant difference (p=0.002) and the DMax was almost significant (p=0.053) suggests that the mesh approach should be adopted to provide accurate comparison between 3D anatomical structures of interest in RT. [ABSTRACT FROM PUBLISHER]
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- 2012
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158. Approximate string matching using phase correlation.
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Alba, Alfonso, Rodriguez-Kessler, Margarita, Arce-Santana, Edgar R., and Mendez, Martin O.
- Abstract
A novel method for approximate string matching with applications to bioinformatics is presented in this paper. Unlike most methods in the literature, the proposed method does not depend on the computation of the edit distance between two sequences, but uses instead a similarity index obtained by applying the phase correlation method. The resulting algorithm provides a finer control over the false positive rate, allowing users to pick out relevant matchings in less time, and can be applied for both offline and online processing. [ABSTRACT FROM PUBLISHER]
- Published
- 2012
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159. Assessment of the Heart Rate Variability during Arousal from Sleep by Cohen's Class Time-Frequency Distributions.
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Jarm, Tomaz, Kramar, Peter, Zupanic, Anze, Mendez, Martin, Bianchi, A.M., Villantieri, O.P., and Cerutti, S.
- Abstract
Arousal from sleep is a normal physiologic event which produces well defined changes in the sympatho-vagal balance. Arousal from sleep is related to sleep fragmentation and some sleep disorders as obstructive sleep apnea. However when repetitive arousals are found during sleep time, bad sleep quality and as consequence sleepiness during the day are associated. We studied the dynamic of the HRV during arousal accompanied by muscular activity. Ten isolated arousals free from any pathologic event where studied. Three Time- Frequency distributions (TFDs), Born-Jordan, Choi-Williams and Smooth Pseudo Wigner-Ville Distributions, were analyzed in order to evaluate their performance during arousal episodes. The three TFDs showed the same performance when analytic HRV signal is used. LF component suggests a major participation of the sympathetic activity at the beginning of the arousal episode while HF component suggests a major role of the parasympathetic drive at after arousal episode. [ABSTRACT FROM AUTHOR]
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- 2007
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160. A Fully Constrained Optimization Method for Time-Resolved Multispectral Fluorescence Lifetime Imaging Microscopy Data Unmixing.
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Gutierrez-Navarro, Omar, Campos-Delgado, Daniel U., Arce-Santana, Edgar, Mendez, Martin O., and Jo, Javier A.
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FLUORESCENCE microscopy ,TIME-domain analysis ,CONSTRAINED optimization ,TIME-resolved measurements ,LEAST squares ,SIMULATION methods & models ,FLUORESCENT dyes ,HYPERSPECTRAL imaging systems - Abstract
This paper presents a new unmixing methodology of multispectral fluorescence lifetime imaging microscopy (m-FLIM) data, in which the spectrum is defined as the combination of time-domain fluorescence decays at multiple emission wavelengths. The method is based on a quadratic constrained optimization (CO) algorithm that provides a closed-form solution under equality and inequality restrictions. In this paper, it is assumed that the time-resolved fluorescence spectrum profiles of the constituent components are linearly independent and known a priori. For comparison purposes, the standard least squares (LS) solution and two constrained versions nonnegativity constrained least squares (NCLS) and fully constrained least squares (FCLS) (Heinz and Chang, 2001) are also tested. Their performance was evaluated by using synthetic simulations, as well as imaged samples from fluorescent dyes and ex vivo tissue. In all the synthetic evaluations, the CO obtained the best accuracy in the estimations of the proportional contributions. CO could achieve an improvement ranging between 41% and 59% in the relative error compared to LS, NCLS, and FCLS at different signal-to-noise ratios. A liquid mixture of fluorescent dyes was also prepared and imaged in order to provide a controlled scenario with real data, where CO and FCLS obtained the best performance. The CO and FCLS were also tested with 20 ex vivo samples of human coronary arteries, where the expected concentrations are qualitatively known. A certainty measure was employed to assess the confidence in the estimations made by each algorithm. The experiments confirmed a better performance of CO, since this method is optimal with respect to equality and inequality restrictions in the linear unmixing formulation. Thus, the evaluation showed that CO achieves an accurate characterization of the samples. Furthermore, CO is a computational efficient alternative to estimate the abundance of components in m-FLIM data, since a global optimal solution is always guaranteed in a closed form. [ABSTRACT FROM PUBLISHER]
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- 2013
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161. Conservation genetics of harvested river turtles, Podocnemis expansa and Podocnemis unifilis, in the Peruvian Amazon: All roads lead to Iquitos.
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Pineda-Catalan, Oscar, Mendez, Martin, Gleizer, Anya, García-Dávila, Carmen, Aguirre, A. Alonso, Pinedo-Vasquez, Miguel, and Amato, George
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TURTLES , *PODOCNEMIS expansa , *PODOCNEMIS unifilis , *MITOCHONDRIAL DNA analysis , *HAPLOTYPES , *PROTECTED areas - Abstract
We present a mtDNA analysis of Podocnemis expansa ( n = 81) and Podocnemis unifilis ( n = 228) turtles traded in Peru to evaluate the potential origin of these animals. In particular, we were interested in the relationship between samples reported in the Iquitos markets (IMs) and a Pacaya Samiria Natural Reserve (PSNR) where illegal hunting is presumed. Our mtDNA data showed that, for both species, all haplotypes found within the PSNR were observed in the IM, and that these markets also displayed haplotypes not documented in the reserve. This suggests that the IMs are recipients of Podocnemis turtles from within and outside the PSNR. The fact that most of the haplotype diversity observed in the markets was not found within the PSNR strongly suggests that Podocnemis genetic diversity is exploited in areas where conservation actions are limited. Hence, we recommend expanding Podocnemis conservation efforts outside of protected areas. [ABSTRACT FROM AUTHOR]
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- 2012
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162. Pneumonia without the need for admission, the experience in an emergency department
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Arévalo-Velasco, Agustín, Alario-García, María J., Méndez-Martín, Violante, and García-García, Ángel
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- 2012
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163. Mechanical properties, microstructure and thermal stability of a nanocrystalline CoCrFeMnNi high-entropy alloy after severe plastic deformation
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Schuh, B., Mendez-Martin, F., Völker, B., George, E.P., Clemens, H., Pippan, R., and Hohenwarter, A.
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Polymers and Plastics ,High-entropy alloys ,Severe plastic deformation ,Metals and Alloys ,Ceramics and Composites ,3 dimensional atom probe tomography ,Compositionally complex alloys ,Microstructure ,Electronic, Optical and Magnetic Materials - Abstract
An equiatomic CoCrFeMnNi high-entropy alloy (HEA), produced by arc melting and drop casting, was subjected to severe plastic deformation (SPD) using high-pressure torsion. This process induced substantial grain refinement in the coarse-grained casting leading to a grain size of approximately 50nm. As a result, strength increased significantly to 1950MPa, and hardness to ∼520HV. Analyses using transmission electron microscopy (TEM) and 3-dimensional atom probe tomography (3D-APT) showed that, after SPD, the alloy remained a true single-phase solid solution down to the atomic scale. Subsequent investigations characterized the evolution of mechanical properties and microstructure of this nanocrystalline HEA upon annealing. Isochronal (for 1h) and isothermal heat treatments were performed followed by microhardness and tensile tests. The isochronal anneals led to a marked hardness increase with a maximum hardness of ∼630HV at about 450°C before softening set in at higher temperatures. The isothermal anneals, performed at this peak hardness temperature, revealed an additional hardness rise to a maximum of about 910HV after 100h. To clarify this unexpected annealing response, comprehensive microstructural analyses were performed using TEM and 3D-APT. New nano-scale phases were observed to form in the originally single-phase HEA. After times as short as 5min at 450°C, a NiMn phase and Cr-rich phase formed. With increasing annealing time, their volume fractions increased and a third phase, FeCo, also formed. It appears that the surfeit of grain boundaries in the nanocrystalline HEA offer many fast diffusion pathways and nucleation sites to facilitate this phase decomposition. The hardness increase, especially for the longer annealing times, can be attributed to these nano-scaled phases embedded in the HEA matrix. The present results give new valuable insights into the phase stability of single-phase high-entropy alloys as well as the mechanisms controlling the mechanical properties of nanostructured multiphase composites.
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164. Fibrosis of the Gluteal Muscles
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H. Duran Sacristan, L. Ferrandez, A. Sanchez-Barba, J. Mendez Martin, C. Linan, and L. Lopez-Duran Stern
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medicine.anatomical_structure ,Text mining ,Fibrosis ,business.industry ,medicine ,Orthopedics and Sports Medicine ,Surgery ,General Medicine ,Anatomy ,Gluteal muscles ,medicine.disease ,business - Published
- 1974
165. [Nutritional effect of essential amino acid supplement during hemodialysis]
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A, Ortiz Gonzalez, M P, Sanchez-Robles, J R, Gutierrez Gonzalez, and A, Mendez Martin
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Adult ,Nitrogen ,Renal Dialysis ,Humans ,Histidine ,Nutritional Physiological Phenomena ,Amino Acids, Essential ,Middle Aged ,Nutrition Disorders - Published
- 1983
166. High-resolution characterization of intermetallic TiAl-powder for additive manufacturing
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David Wimler, Gammer, C., Eckert, J., Mendez-Martin, F., Lindemann, J., Clemens, H., and Mayer, S.
167. Creep strength and microstructural evolution of 9-12%Cr heat resistant steels during creep exposure at 600°C and 650°C
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Francisca Mendez Martin, Clara Panait, Walter Bendick, Mihaela Albu, Bernhard Sonderegger, Gerald Kothleitner, Christof Sommitsch, Anne-Françoise Gourgues-Lorenzon, Jacques Besson, Fuchsmann, A., Centre des Matériaux (MAT), MINES ParisTech - École nationale supérieure des mines de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), V & M France CEV, Salzgitter Mannesmann Forschung GmbH, J. Lecomte-Beckers, Q. Contrepois, T. Beck, and B. Kuhn
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9% Cr tempered martensitic steels ,laves phases ,creep strength ,12% Cr tempered martensitic steels ,ComputingMilieux_MISCELLANEOUS ,Z phases ,[SPI.MAT]Engineering Sciences [physics]/Materials - Abstract
International audience
168. Giant hardening response in AlMgZn(Cu) alloys
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Stefan Pogatscher, Francisca Mendez-Martin, Matheus A. Tunes, Peter J. Uggowitzer, Ramona Tosone, Daniel Marchand, Phillip Dumitraschkewitz, William A. Curtin, and Lukas Stemper
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Materials science ,Polymers and Plastics ,Alloy ,Nucleation ,02 engineering and technology ,engineering.material ,01 natural sciences ,thermomechanical treatment ,Precipitation hardening ,0502 economics and business ,0103 physical sciences ,Formability ,microstructure evolution ,050207 economics ,Composite material ,Tensile testing ,010302 applied physics ,aluminum alloys ,050208 finance ,Precipitation (chemistry) ,05 social sciences ,Metals and Alloys ,021001 nanoscience & nanotechnology ,Electronic, Optical and Magnetic Materials ,mechanical testing ,Ceramics and Composites ,engineering ,Hardening (metallurgy) ,Thermomechanical processing ,Deformation (engineering) ,0210 nano-technology ,precipitation hardening - Abstract
This study presents a thermomechanical processing concept which is capable of exploiting the full industrial application potential of recently introduced AlMgZn(Cu) alloys. The beneficial linkage of alloy design and processing allows not only to satisfy the long-standing trade-off between high mechanical strength in use and good formability during processing but also addresses the need for economically feasible processing times. After an only 3-hour short pre-aging treatment at 100 degrees C, the two investigated alloys, based on commercial EN AW-5182 and modified with additions of Zn and Zn+Cu respectively, show high formability due to increased work-hardening. Then, these alloys exhibit a giant hardening response of up to 184 MPa to reach a yield strength of 410 MPa after a 20-minute short final heat treatment at 185 degrees C, i.e. paint-baking. This rapid hardening response strongly depends on the number density, size distribution and constitution of precursors acting as preferential nucleation sites for T-phase precursor precipitation during the final high-temperature aging treatment and is significantly increased by the addition of Cu. Minor deformation (2%) after pre-aging and before final heat treatment further enhances the development of hardening precipitates additionally by activating dislocation-supported nucleation and growth. Tensile testing, quantitative and analytical electron-microscopy methods, atom probe analysis and DFT calculations were used to characterize the alloys investigated in this work over the thermomechanical processing route. The influence of pre-strain on the hardening response and the role of Cu additions in early-stage cluster nucleation are discussed in detail and supported by in-situ STEM experiments and first-principles calculations. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd.
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169. On the existence of orthorhombic martensite in a near-α titanium base alloy used for additive manufacturing
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Christian Fleißner-Rieger, Matheus Araujo Tunes, Christoph Gammer, Tanja Jörg, Tanja Pfeifer, Michael Musi, Francisca Mendez-Martin, and Helmut Clemens
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010302 applied physics ,Mechanics of Materials ,Mechanical Engineering ,0103 physical sciences ,Materials Chemistry ,Metals and Alloys ,02 engineering and technology ,021001 nanoscience & nanotechnology ,0210 nano-technology ,01 natural sciences - Full Text
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170. SEM and FIB-SEM investigations on potential gas shales in the Dniepr-Donets Basin (Ukraine): pore space evolution in organic matter during thermal maturation.
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D Misch, F Mendez-Martin, G Hawranek, P Onuk, D Gross, and R F Sachsenhofer
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- 2016
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171. Community-Driven Methods for Open and Reproducible Software Tools for Analyzing Datasets from Atom Probe Microscopy.
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Kühbach M, London AJ, Wang J, Schreiber DK, Mendez Martin F, Ghamarian I, Bilal H, and Ceguerra AV
- Abstract
Atom probe tomography, and related methods, probe the composition and the three-dimensional architecture of materials. The software tools which microscopists use, and how these tools are connected into workflows, make a substantial contribution to the accuracy and precision of such material characterization experiments. Typically, we adapt methods from other communities like mathematics, data science, computational geometry, artificial intelligence, or scientific computing. We also realize that improving on research data management is a challenge when it comes to align with the FAIR data stewardship principles. Faced with this global challenge, we are convinced it is useful to join forces. Here, we report the results and challenges with an inter-laboratory call for developing test cases for several types of atom probe microscopy software tools. The results support why defining detailed recipes of software workflows and sharing these recipes is necessary and rewarding: Open source tools and (meta)data exchange can help to make our day-to-day data processing tasks become more efficient, the training of new users and knowledge transfer become easier, and assist us with automated quantification of uncertainties to gain access to substantiated results.
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- 2021
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172. Fluorescence background removal method for biological Raman spectroscopy based on empirical mode decomposition.
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Leon-Bejarano M, Dorantes-Mendez G, Ramirez-Elias M, Mendez MO, Alba A, Rodriguez-Leyva I, and Jimenez M
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- Algorithms, Fluorescence, Humans, Signal-To-Noise Ratio, Skin chemistry, Signal Processing, Computer-Assisted, Spectrum Analysis, Raman methods
- Abstract
Raman spectroscopy of biological tissue presents fluorescence background, an undesirable effect that generates false Raman intensities. This paper proposes the application of the Empirical Mode Decomposition (EMD) method to baseline correction. EMD is a suitable approach since it is an adaptive signal processing method for nonlinear and non-stationary signal analysis that does not require parameters selection such as polynomial methods. EMD performance was assessed through synthetic Raman spectra with different signal to noise ratio (SNR). The correlation coefficient between synthetic Raman spectra and the recovered one after EMD denoising was higher than 0.92. Additionally, twenty Raman spectra from skin were used to evaluate EMD performance and the results were compared with Vancouver Raman algorithm (VRA). The comparison resulted in a mean square error (MSE) of 0.001554. High correlation coefficient using synthetic spectra and low MSE in the comparison between EMD and VRA suggest that EMD could be an effective method to remove fluorescence background in biological Raman spectra.
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- 2016
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173. Methods for heart rate variability analysis during sleep.
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Bianchi AM and Mendez MO
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- Data Interpretation, Statistical, Female, Humans, Polysomnography, Heart Rate, Sleep physiology
- Abstract
In the last years we have witnessed the growing interest in the heart rate variability (HRV) signal analysis during sleep. The study of the autonomic regulation during sleep allowed developing methods for automatic detection and classification of some sleep characteristics, both in physiological and pathological conditions. The main problems which require to be faced are the presence of frequent non-stationarities in the signal and the need of dealing with long term analysis, in order to provide reliable indices able to describe the whole night of sleep. In the present paper we are presenting some of the methodologies we recently employed in the study of the heart rate variability during sleep, ranging from time-frequency analysis to long time correlation. Some results are also presented, related to different applications, dealing with both physiological and pathological conditions.
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- 2013
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174. Efficient automatic classifiers for the detection of A phases of the cyclic alternating pattern in sleep.
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Mariani S, Manfredini E, Rosso V, Grassi A, Mendez MO, Alba A, Matteucci M, Parrino L, Terzano MG, Cerutti S, and Bianchi AM
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- Adult, Algorithms, Electroencephalography methods, Female, Humans, Male, Neural Networks, Computer, Polysomnography methods, Support Vector Machine, Signal Processing, Computer-Assisted, Sleep Stages physiology
- Abstract
This study aims to develop an automatic detector of the A phases of the cyclic alternating pattern, periodic activity that generally occurs during non-REM (NREM) sleep. Eight polysomnographic recordings from healthy subjects were examined. From EEG recordings, five band descriptors, an activity descriptor and a variance descriptor were extracted and used to train different machine-learning algorithms. A visual scoring provided by an expert clinician was used as golden standard. Four alternative mathematical machine-learning techniques were implemented: (1) discriminant classifier, (2) support vector machines, (3) adaptive boosting, and (4) supervised artificial neural network. The results of the classification, compared with the visual analysis, showed average accuracies equal to 84.9 and 81.5% for the linear discriminant and the neural network, respectively, while AdaBoost had a slightly lower accuracy, equal to 79.4%. The SVM leads to accuracy of 81.9%. The performance achieved by the automatic classification is encouraging, since an efficient automatic classifier would benefit the practice in everyday clinics, preventing the physician from the time-consuming activity of the visually scoring of the sleep microstructure over whole 8-h sleep recordings. Finally, the classification based on learning algorithms would provide an objective criterion, overcoming the problems of inter-scorer disagreement.
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- 2012
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175. Study of Heart Rate Variability in Bipolar Disorder: Linear and Non-Linear Parameters during Sleep.
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Migliorini M, Mendez MO, and Bianchi AM
- Abstract
The aim of the study is to define physiological parameters and vital signs that may be related to the mood and mental status in patients affected by bipolar disorder. In particular we explored the autonomic nervous system through the analysis of the heart rate variability. Many different parameters, in the time and in the frequency domain, linear and non-linear were evaluated during the sleep in a group of normal subject and in one patient in four different conditions. The recording of the signals was performed through a wearable sensorized T-shirt. Heart rate variability (HRV) signal and movement analysis allowed also obtaining sleep staging and the estimation of REM sleep percentage over the total sleep time. A group of eight normal females constituted the control group, on which normality ranges were estimated. The pathologic subject was recorded during four different nights, at time intervals of at least 1 week, and during different phases of the disturbance. Some of the examined parameters (MEANNN, SDNN, RMSSD) confirmed reduced HRV in depression and bipolar disorder. REM sleep percentage was found to be increased. Lempel-Ziv complexity and sample entropy, on the other hand, seem to correlate with the depression level. Even if the number of examined subjects is still small, and the results need further validation, the proposed methodology and the calculated parameters seem promising tools for the monitoring of mood changes in psychiatric disorders.
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- 2012
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176. Mesh-based approach for the 3D analysis of anatomical structures of interest in radiotherapy.
- Author
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Mejia-Rodriguez AR, Scalco E, Tresoldi D, Bianchi AM, Arce-Santana ER, Mendez MO, and Rizzo G
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- Algorithms, Computer Simulation, Electronic Data Processing, Humans, Image Processing, Computer-Assisted, Models, Anatomic, Models, Statistical, Observer Variation, Parotid Gland pathology, Radiographic Image Interpretation, Computer-Assisted methods, Signal Processing, Computer-Assisted, Tomography, X-Ray Computed methods, Imaging, Three-Dimensional methods, Parotid Gland diagnostic imaging, Radiotherapy methods, Radiotherapy Planning, Computer-Assisted methods
- Abstract
In this paper a method based on mesh surfaces approximations for the 3D analysis of anatomical structures in Radiotherapy (RT) is presented. Parotid glands meshes constructed from Megavoltage CT (MVCT) images were studied in terms of volume, distance between center of mass (distCOM) of the right and left parotids, dice similarity coefficient (DICE), maximum distance between meshes (DMax) and the average symmetric distance (ASD). A comparison with the standard binary images approach was performed. While absence of significant differences in terms of volume, DistCOM and DICE indices suggests that both approaches are comparable, the fact that the ASD showed significant difference (p=0.002) and the DMax was almost significant (p=0.053) suggests that the mesh approach should be adopted to provide accurate comparison between 3D anatomical structures of interest in RT.
- Published
- 2012
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177. Approximate string matching using phase correlation.
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Alba A, Rodriguez-Kessler M, Arce-Santana ER, and Mendez MO
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- Algorithms, Amino Acid Sequence, Molecular Sequence Data, Proteins chemistry, Computational Biology, Pattern Recognition, Automated
- Abstract
A novel method for approximate string matching with applications to bioinformatics is presented in this paper. Unlike most methods in the literature, the proposed method does not depend on the computation of the edit distance between two sequences, but uses instead a similarity index obtained by applying the phase correlation method. The resulting algorithm provides a finer control over the false positive rate, allowing users to pick out relevant matchings in less time, and can be applied for both offline and online processing.
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- 2012
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178. Characterization of A phases during the cyclic alternating pattern of sleep.
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Mariani S, Manfredini E, Rosso V, Mendez MO, Bianchi AM, Matteucci M, Terzano MG, Cerutti S, and Parrino L
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- Adult, Female, Humans, Male, Polysomnography methods, Sleep physiology, Young Adult, Electroencephalography methods, Periodicity, Sleep Stages physiology
- Abstract
Objective: This study aims to identify, starting from a single EEG trace, quantitative distinctive features characterizing the A phases of the Cyclic Alternating Pattern (CAP)., Methods: The C3-A2 or C4-A1 EEG leads of the night recording of eight healthy adult subjects were used for this analysis. CAP was scored by an expert and the portions relative to NREM were selected. Nine descriptors were computed: band descriptors (low delta, high delta, theta, alpha, sigma and beta); Hjorth activity in the low delta and high delta bands; differential variance of the EEG signal. The information content of each descriptor in recognizing the A phases was evaluated through the computation of the ROC curves and the statistics sensitivity, specificity and accuracy., Results: The ROC curves show that all the descriptors have a certain significance in characterizing A phases. The average accuracy obtained by thresholding the descriptors ranges from 59.89 (sigma descriptor) to 72.44 (differential EEG variance)., Conclusions: The results show that it is possible to attribute a significant quantitative value to the information content of the descriptors., Significance: This study gives a mathematical confirm to the features of CAP generally described qualitatively, and puts the bases for the creation of automatic detection methods., (Copyright © 2011 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)
- Published
- 2011
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179. Automatic detection of CAP on central and fronto-central EEG leads via Support Vector Machines.
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Mariani S, Grassi A, Mendez MO, Parrino L, Terzano MG, and Bianchi AM
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- Adult, Algorithms, Female, Humans, Male, Reproducibility of Results, Sensitivity and Specificity, Activity Cycles physiology, Biological Clocks physiology, Brain physiology, Diagnosis, Computer-Assisted methods, Electroencephalography methods, Pattern Recognition, Automated methods, Support Vector Machine
- Abstract
The aim of this study is to implement a high-accuracy automatic detector of the Cyclic Alternating Pattern (CAP) during sleep. EEG data from four healthy subjects were used. Both the C4-A1 and the F4-C4 leads were analyzed for this study. Seven features were extracted from each of the two leads and two separate studies were performed for each set of descriptors. For both sets, a Support Vector Machine was trained and tested on the data with the Leave One Out cross-validation method. The two final classifications obtained on the two sets were merged, by considering a CAP A phase scored only if it had been recognized both on the central and on the frontal lead. The length of the A phase was then determined by the result on the fronto-central lead. This method leads to encouraging results, with a classification sensitivity on the whole dataset equal to 73.82%, specificity equal to 85.93%, accuracy equal to 84,05% and Cohen's kappa equal to 0.50.
- Published
- 2011
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180. Automatic sleep staging based on ballistocardiographic signals recorded through bed sensors.
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Migliorini M, Bianchi AM, Nisticò D, Kortelainen J, Arce-Santana E, Cerutti S, and Mendez MO
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- Adult, Algorithms, Beds, Diagnosis, Computer-Assisted instrumentation, Female, Humans, Polysomnography instrumentation, Reproducibility of Results, Sensitivity and Specificity, Transducers, Ballistocardiography methods, Diagnosis, Computer-Assisted methods, Pattern Recognition, Automated methods, Polysomnography methods, Sleep Stages physiology
- Abstract
This study presents different methods for automatic sleep classification based on heart rate variability (HRV), respiration and movement signals recorded through bed sensors. Two methods for feature extraction have been implemented: time variant-autoregressive model (TVAM) and wavelet discrete transform (WDT); the obtained features are fed into two classifiers: Quadratic (QD) and Linear (LD) discriminant for staging sleep in REM, nonREM and WAKE periods. The performances of all the possible combinations of feature extractors and classifiers are compared in terms of accuracy and kappa index, using clinical polysomographyc evaluation as golden standard. 17 recordings from healthy subjects, including also polisomnography, were used to train and test the algorithms. When automatic classification is compared. QD-TVAM algorithm achieved a total accuracy of 76.81 ± 7.51 % and kappa index of 0.55 ± 0.10, while LD-WDT achieved a total accuracy of 79 ± 10% and kappa index of 0.51 ± 0.17. The results suggest that a good sleep evaluation can be achieved through non-conventional recording systems that could be used outside sleep centers.
- Published
- 2010
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181. Automatic detection of sleep macrostructure based on a sensorized T-shirt.
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Bianchi AM and Mendez MO
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- Algorithms, Humans, Textiles, Clothing, Diagnosis, Computer-Assisted instrumentation, Diagnosis, Computer-Assisted methods, Monitoring, Ambulatory instrumentation, Polysomnography instrumentation, Sleep Stages physiology
- Abstract
In the present work we apply a fully automatic procedure to the analysis of signal coming from a sensorized T-shit, worn during the night, for sleep evaluation. The goodness and reliability of the signals recorded trough the T-shirt was previously tested, while the employed algorithms for feature extraction and sleep classification were previously developed on standard ECG recordings and the obtained classification was compared to the standard clinical practice based on polysomnography (PSG). In the present work we combined T-shirt recordings and automatic classification and could obtain reliable sleep profiles, i.e. the sleep classification in WAKE, REM (rapid eye movement) and NREM stages, based on heart rate variability (HRV), respiration and movement signals.
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- 2010
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182. Evaluation of the sleep quality based on bed sensor signals: Time-variant analysis.
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Mendez MO, Migliorini M, Kortelainen JM, Nistico D, Arce-Santana E, Cerutti S, and Bianchi AM
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- Automation, Feasibility Studies, Humans, Polysomnography, Sleep
- Abstract
Automatic detection of the sleep macrostructure (Wake, NREM -non Rapid Eye Movement- and REM -Rapid Eye Movement-) based on bed sensor signals is presented. This study assesses the feasibility of different methodologies to evaluate the sleep quality out of sleep centers. The study compares a) the features extracted from time-variant autoregressive modeling (TVAM) and Wavelet Decomposition (WD) and b) the performance of K-Nearest Neighbor (KNN) and Feed Forward Neural Networks (FFNN) classifiers. In the current analysis, 17 full polysomnography recordings from healthy subjects were used. The best agreement for Wake-NREM-REM with respect to the gold standard was 71.95 ± 7.47% of accuracy and 0.42 ± 0.10 of kappa index for TVAM-LD while WD-FFNN shows 67.17 ± 11.88% of accuracy and 0.39 ± 0.13 of kappa index. The results suggest that the sleep quality assessment out of sleep centers could be possible and as consequence more people could be beneficiated.
- Published
- 2010
- Full Text
- View/download PDF
183. Automatic detection of a phases of the cyclic alternating pattern during sleep.
- Author
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Mariani S, Bianchi AM, Manfredini E, Rosso V, Mendez MO, Parrino L, Matteucci M, Grassi A, Cerutti S, and Terzano MG
- Subjects
- Adult, Humans, Neural Networks, Computer, Automation methods, Electroencephalography methods, Sleep Stages physiology
- Abstract
This study aimed to develop an automatic algorithm to detect the activation phases (A phases) of the Cyclic Alternating Pattern. The sleep EEG microstructure of 4 adult, healthy subjects was scored by a sleep medicine expert. Features were calculated from each of the six EEG bands (low delta, high delta, theta, alpha, sigma and beta), and three additional characteristics were computed: the Hjorth activity in the low delta and high delta bands, and the differential variance of the raw EEG signal. The correlation between couples of features was analyzed to find redundancies for the automatic analysis. The features were used to train an Artificial Neural Network to automatically find the A phases of CAP. The data were divided into training, validation and testing set, and the visual scoring provided by the clinician was used as the desired output. The statistics on the second by second classification show an average sensitivity equal to 76%, specificity equal to 83% and accuracy equal to 82%. The results obtained are encouraging, since an automatic classification of the A phases could benefit the practice in clinics, preventing the physician from the time-consuming activity of visually scoring the sleep microstructure over the whole eight-hour sleep recordings. Moreover, it would provide an objective criterion capable of overcoming the problems of inter-scorer variability.
- Published
- 2010
- Full Text
- View/download PDF
184. Sleep apnea screening by autoregressive models from a single ECG lead.
- Author
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Mendez MO, Bianchi AM, Matteucci M, Cerutti S, and Penzel T
- Subjects
- Adult, Computer Simulation, Data Interpretation, Statistical, Electrocardiography instrumentation, Female, Humans, Male, Middle Aged, Models, Biological, Models, Statistical, Regression Analysis, Reproducibility of Results, Sensitivity and Specificity, Algorithms, Diagnosis, Computer-Assisted methods, Electrocardiography methods, Mass Screening methods, Sleep Apnea Syndromes diagnosis
- Abstract
This paper presents a method for obstructive sleep apnea (OSA) screening based on the electrocardiogram (ECG) recording during sleep. OSA is a common sleep disorder produced by repetitive occlusions in the upper airways and this phenomenon can usually be observed also in other peripheral systems such as the cardiovascular system. Then the extraction of ECG characteristics, such as the RR intervals and the area of the QRS complex, is useful to evaluate the sleep apnea in noninvasive way. In the presented analysis, 50 recordings coming from the apnea Physionet database were used; data were split into two sets, the training and the testing set, each of which was composed of 25 recordings. A bivariate time-varying autoregressive model (TVAM) was used to evaluate beat-by-beat power spectral densities for both the RR intervals and the QRS complex areas. Temporal and spectral features were changed on a minute-by-minute basis since apnea annotations where given with this resolution. The training set consisted of 4950 apneic and 7127 nonapneic minutes while the testing set had 4428 apneic and 7927 nonapneic minutes. The K-nearest neighbor (KNN) and neural networks (NN) supervised learning classifiers were employed to classify apnea and non apnea minutes. A sequential forward selection was used to select the best feature subset in a wrapper setting. With ten features the KNN algorithm reached an accuracy of 88%, sensitivity equal to 85%, and specificity up to 90%, while NN reached accuracy equal to 88%, sensitivity equal to 89% and specificity equal to 86%. In addition to the minute-by-minute classification, the results showed that the two classifiers are able to separate entirely (100%) the normal recordings from the apneic recordings. Finally, an additional database with eight recordings annotated as normal or apneic was used to test again the classifiers. Also in this new dataset, the results showed a complete separation between apneic and normal recordings.
- Published
- 2009
- Full Text
- View/download PDF
185. Detection of obstructive sleep apnea in children using decreases in the amplitude fluctuations of PPG signal and HRV.
- Author
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Gil E, Mendez M, Vergara JM, Cerutti S, Bianchi AM, and Laguna P
- Subjects
- Algorithms, Child, Preschool, Electrophysiology methods, Female, Humans, Male, Oximetry methods, Reproducibility of Results, Sensitivity and Specificity, Signal Processing, Computer-Assisted, Diagnosis, Computer-Assisted methods, Heart Rate, Photoplethysmography methods, Sleep Apnea, Obstructive diagnosis, Sleep Apnea, Obstructive physiopathology
- Abstract
An analysis of the HRV during decreases in the amplitude fluctuations of PPG (DAP) events, and their utility in OSAS screening is presented. The overall data set used in the study includes the polysomnographic records of 21 children. DAP events were automatically detected by an algorithm based on the envelope attenuations of the PPG. DAP events were classified as apneic or non apneic by a linear discriminant analysis. The features used by the linear discriminant come from the temporal and spectral parameters of the heart rate obtained by Smooth Pseudo Wigner Ville Distribution. Two indexes were defined: the number of DAP events per hour ratio r(DAP) and the number of apneic DAP events per hour ratio r(DAP)(alpha). Results show a 12% increase in accuracy for r(DAP)(alpha) with respect to r(DAP) in classifying 1 hour polysomnographic segments, reaching values of 72.7% and 80% for sensitivity and specificity, respectively. As for subject classification, the improvement in accuracy is 6.7% obtaining values of 87.5% and 71.4% for sensitivity and specificity respectively. These results suggest that the combination of DAP and HRV could be an alternative for sleep apnea screening with the added benefit of low cost and simplicity.
- Published
- 2008
- Full Text
- View/download PDF
186. Detection of sleep apnea from surface ECG based on features extracted by an autoregressive model.
- Author
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Mendez MO, Ruini DD, Villantieri OP, Matteucci M, Penzel T, Cerutti S, and Bianchi AM
- Subjects
- Computer Simulation, Data Interpretation, Statistical, Expert Systems, Female, Humans, Male, Models, Statistical, Pattern Recognition, Automated methods, Regression Analysis, Reproducibility of Results, Sensitivity and Specificity, Algorithms, Diagnosis, Computer-Assisted methods, Electrocardiography methods, Heart Rate, Models, Neurological, Sleep Apnea Syndromes diagnosis, Sleep Apnea Syndromes physiopathology
- Abstract
This study proposes an alternative evaluation of Obstructive Sleep Apnea (OSA) based on ECG signal during sleep time. OSA is a common sleep disorder produced by repetitive occlusions in the upper airways. This respiratory disturbance produces a specific pattern on ECG. Extraction of ECG characteristics, as Heart Rate Variability (HRV) and peak R area, offers alternative measures for a sleep apnea pre-diagnosis. 50 recordings coming from the apnea Physionet database were used in the analysis, this database is part of the 70 recordings used for the Computer in Cardiology challenge celebrated in 2000. A bivariate autoregressive model was used to evaluate beat-by-beat power spectral density of HRV and R peak area. K-Nearest Neighbor (KNN) supervised learning classifier was employed for categorizing apnea events from normal ones, on a minute-by-minute basis for each recording. Data were split into two sets, training and testing set, each one with 25 recordings. The classification results showed an accuracy higher than 85% in both training and testing. In addition it was possible to separate completely between Apnea and Normal subjects and almost completely among Apnea, Normal and Borderline subjects.
- Published
- 2007
- Full Text
- View/download PDF
187. Sleep monitoring through a textile recording system.
- Author
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Devot S, Bianchi AM, Naujokat E, Mendez MO, Braurs A, and Cerutti S
- Subjects
- Humans, Polysomnography instrumentation, Electrocardiography methods, Polysomnography methods, Respiration, Sleep physiology, Textiles
- Abstract
In this paper, we present a home device for the continuous monitoring of sleep and investigate its reliability regarding sleep evaluation. The system has been particularly designed for healthy people and for preventive purposes. It is not obtrusive and therefore can be used every night without impeding sleep in itself and without interfering with the normal way of life. The signal used for sleep evaluation is the HRV derived from the ECG recorded by means of a sheet and a pillow. Patients in a sleep lab and healthy subjects at home were monitored during sleep with the textile system, while also standard ECG and respiration were recorded. For the textile ECG sensor, coverage of the signal on a beat-to-beat basis ranged from 47,9 - 95,8% of the overall night for the healthy subjects, with a mean coverage of 81,8%. In the group of sleep laboratory patients, the mean coverage was lower - 64,4% - although even in this group the coverage of a single night ranged up to 98.4%. After frequency analysis, the spectral parameters used for sleep staging and derived at the same time from standard and textile ECG signals were compared. The trends along the night are very similar, indicating the possibility of using textile HRV for sleep evaluation.
- Published
- 2007
- Full Text
- View/download PDF
188. Signal processing and feature extraction for sleep evaluation in wearable devices.
- Author
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Bianchi AM, Villantieri OP, Mendez MO, and Cerutti S
- Subjects
- Analysis of Variance, Arousal, Autonomic Nervous System physiopathology, Biomedical Engineering, Case-Control Studies, Continuous Positive Airway Pressure, Heart Rate, Humans, Polysomnography instrumentation, Polysomnography statistics & numerical data, Respiration, Signal Processing, Computer-Assisted, Sleep Apnea, Obstructive diagnosis, Sleep Apnea, Obstructive physiopathology, Sleep Apnea, Obstructive therapy, Polysomnography methods
- Abstract
In this paper we discuss the possibility of performing a sleep evaluation form the heart rate variability (HRV) and respiratory signals. This is particularly useful for wearable devices. The HRV and the respiration were analyzed in the frequency domain and the statistics on the spectral and cross-spectral parameters put into evidence the possibility of a sleep evaluation on their basis. Additional information can be achieved from the number of microarousals recognized in correspondence of typical modifications in the HRV signal.
- Published
- 2006
- Full Text
- View/download PDF
189. [Nutritional effect of essential amino acid supplement during hemodialysis].
- Author
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Ortiz Gonzalez A, Sanchez-Robles MP, Gutierrez Gonzalez JR, and Mendez Martin A
- Subjects
- Adult, Histidine administration & dosage, Humans, Middle Aged, Nitrogen metabolism, Nutrition Disorders diet therapy, Amino Acids, Essential administration & dosage, Nutritional Physiological Phenomena, Renal Dialysis
- Published
- 1983
190. Fibrosis of the gluteal muscles: report of three cases.
- Author
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Duran Sacristan H, Sanchez-Barba A, Lopez-Duran Stern L, Mendez Martin J, Linan C, and Ferrandez L
- Subjects
- Anti-Bacterial Agents administration & dosage, Child, Child, Preschool, Female, Humans, Male, Muscular Atrophy etiology, Muscular Diseases surgery, Buttocks surgery, Injections, Intramuscular adverse effects, Muscular Diseases etiology
- Published
- 1974
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