Biomedical subjects

P Valdés

Publications and source records attributed to P Valdés.

At least 19 recordsLinked to original sources

PubMed2004

Random field-union intersection tests for EEG/MEG imaging.

Electrophysiological (EEG/MEG) imaging challenges statistics by providing two views of the same spatiotemporal data: topographic and tomographic. Until now, statistical tests for these two situations have developed separately. This work introduces statistical tests for assessing simultaneously the significance of spatiotemporal event-related potential/event-related field (ERP/ERF) components and that of their sources. The test for detecting a component at a given time instant is provided by a Hotelling's T(2) statistic. This statistic is constructed in such a manner to be invariant to any choice of reference and is based upon a generalized version of the average reference transform of the data. As a consequence, the proposed test is a generalization of the well-known Global Field Power statistic. Consideration of tests at all time instants leads to a multiple comparison problem addressed by the use of Random Field Theory (RFT). The Union-Intersection (UI) principle is the basis for testing hypotheses about the topographic and tomographic distributions of such ERP/ERF components. The performance of the method is illustrated with actual EEG recordings obtained from a visual experiment of pattern reversal stimuli.

Algorithms↗

PubMed2001

Prospective comparison of clinical and echocardiographic diagnosis of rheumatic carditis: long term follow up of patients with subclinical disease.

OBJECTIVE: To determine the frequency of occurrence and long term evolution of subclinical carditis in patients with acute rheumatic fever. DESIGN: Valvar incompetence was detected by clinical examination and Doppler echocardiographic imaging during the acute and quiescent phases of rheumatic fever. Patients were followed prospectively and submitted to repeat examinations at one and five years after the acute attack. Persistence of acute mitral and aortic lesions detected solely by echocardiography (subclinical disease) was compared with that of disease detected by clinical examination as well (thereby fulfilling the latest 1992 Jones criteria for rheumatic carditis). SETTING: Three general hospitals with a university affiliation in Chile. PATIENTS: 35 consecutive patients fulfilling the revised Jones criteria for rheumatic fever. Clinical and echocardiographic examination was repeated in 32 patients after one year and in 17 after five years. Ten patients had subclinical carditis on admission, six of whom were followed for five years. MAIN OUTCOME MEASURES: Auscultatory and echocardiographic evidence of mitral or aortic regurgitation during the acute attack or at follow up. RESULTS: Mitral or aortic regurgitation was detected by Doppler echocardiographic imaging in 25/35 rheumatic fever patients as opposed to 5/35 by clinical examination (p = 0.03). Doppler echocardiography revealed acute valvar lesions in 10 of 20 rheumatic fever patients who had no auscultatory evidence of rheumatic carditis (subclinical carditis). Three of these subclinical lesions and three of the clinical or auscultatory lesions detected on admission were still present after five years of follow up, emphasising that subclinical lesions are not necessarily transient. CONCLUSIONS: Doppler echocardiographic imaging improves the detection of rheumatic carditis. Subclinical valve lesions, detected only by Doppler imaging, can persist. Echocardiographic findings should be accepted as a major criterion for the diagnosis of rheumatic fever.

Adolescent↗

PubMed2000

Sources of abnormal EEG activity in brain infarctions.

EEGs from 16 patients with stroke in three different stages of evolution were recorded. EEG sources were calculated every 0.39 Hz by frequency domain VARETA. The main source was within the delta band in 2 out of 4 chronic patients, and in 67% of the patients in the acute or subacute stages when edema (cytotoxic or vasogenic) was present. Moreover, all patients showed abnormal activity in the theta band. Sources of abnormal activity in cortical or corticosubcortical infarcts were located in the cortex, surrounding the lesion. At the site of the infarct, a decrease of EEG power was observed. Sources of abnormal theta power coincided with edema and/or ischemic penumbra.

Adult↗

PubMed1999

Do specific EEG frequencies indicate different processes during mental calculation?

EEG recordings during mental calculation and a control task (with presentation of stimuli with similar physical characteristics to the arithmetic symbols) were obtained in 10 subjects. Narrow band analyses of the EEG and distributed sources for each EEG frequency were calculated using variable resolution electromagnetic tomography. Significant differences between the sources for arithmetic and control tasks were observed at 3.9 Hz within Broca's and left parietotemporal cortices, suggesting that this frequency may be related with the production of internal speech, storage and rehearsal of verbal working memory. Differences at 5.46 Hz within the right dorsolateral prefrontal cortex were considered to be associated to sustained attention. The decrease at 12.46 Hz within the left parietal cortex was interpreted as a sign of retrieval of arithmetic facts from long term memory.

Adult↗

PubMed1999

Preregistration study on the safety and contraceptive efficacy of a progesterone-releasing vaginal ring in Chilean nursing women.

The contraceptive efficacy and safety of a progesterone-releasing vaginal ring (PVR) manufactured in Chile were compared to that of the Copper T 380A IUD (T-Cu) in nursing women enrolled at three Chilean clinics. A total of 285 volunteers chose to use the PVR and 262 the T-Cu. Plasma progesterone levels attained with the ring decreased from 25 to 14 nmol/L from month 1 to month 3 of use. Ring replacement was scheduled every 3 months. Volunteers continued in the study until weaning or completing the continuous use of four PVRs. No pregnancies occurred in 2320 and 2183 woman-months of exposure with the PVR and the T-Cu, respectively. Lower continuation rates in the first 6 months because of problems with use and a longer lactational amenorrhea were observed in the PVR than in the T-Cu group. Breast-feeding performance and infant growth were similar in both groups. These results confirm the high efficacy and safety of the PVR for nursing women and have led to the registration of the PVR by Chilean health authorities.

Adult↗

PubMed1999

Sources of abnormal EEG activity in the presence of brain lesions.

In routine clinical EEG, a common origin is assumed for delta and theta rhythms produced by brain lesions. In previous papers, we have provided some experimental support, based on High Resolution qEEG and dipole fitting in the frequency domain, for the hypothesis that delta and theta spectral power have independent origins related to lesion and edema respectively. This paper describes the results obtained with Frequency Domain VARETA (FD-VARETA) in a group of 13 patients with cortical space-occupying lesions, in order to: 1) Test the accuracy of FD-VARETA for the localization of brain lesions, and 2) To provide further support for the independent origin of delta and theta components. FD VARETA is a distributed inverse solution, constrained by the Montreal Neurological Institute probabilistic atlas that estimates the spectra of EEG sources. In all patients, logarithmic transformed source spectra were compared with age-matched normative values, defining the Z source spectrum. Maximum Z values were found in 10 patients within the delta band (1.56 to 3.12 Hz); the spatial extent of these sources in the atlas corresponded with the location of the tumors in the CT. In 2 patients with small metastases and large volumes of edema and in a patient showing only edema, maximum Z values were found between 4.29 and 5.12 Hz. The spatial extent of the sources at these frequencies was within the volume of the edema in the CT. These results provided strong support to the hypothesis that both delta and theta abnormal EEG activities are the counterparts of two different pathophysiological processes.

Brain Edema↗

PubMed1999

[Experience with laparoscopic surgery for adnexal masses at the Regional Hospital of Temuco, Chile].

BACKGROUND: Laparoscopic surgery has clear advantages over open surgical procedures. In gynecology, laparoscopic surgery for adnexal masses in pre or post menopausal women has been used for several years. AIM: To report the experience with gynecologic laparoscopic surgery at the Temuco Regional Hospital. PATIENTS AND METHODS: Between 1996 and 1998, laparoscopic surgery was done in 96 patients aged 16 to 56 years and open surgery in 56 patients aged 15 to 74 years, with a clinical or ultrasound diagnosis of adnexal masses or ovarian dermoid cysts. RESULTS: The most frequent tumors excised were epithelial and germinal cell. Laparoscopic surgery required a mean operative time of 69.9 min and it had a 3.1% of complications. Women subjected to this type of surgery had a mean hospital stay of 3.1 days and the mean postoperative stay was 2 days. Open surgery required an operative time of 69 min and it had no postoperative complications. The mean hospital stay for women subjected to this type of procedure was 9.5 days. CONCLUSIONS: Women subjected to laparoscopic surgical procedures for adnexal masses had a shorter hospital stay than women subjected to open surgical procedures.

Adnexal Diseases↗

PubMed1998

Generalized background qEEG abnormalities in localized symptomatic epilepsy.

Spectral features of EEG background activity were studied in patients with localized symptomatic epilepsy (LSE), with origin in the frontal or temporal lobes. Z-values of high resolution spectra and measures of the parametric (xi alpha) model of the EEG were obtained for all 10/20 System leads and were compared with those obtained in a control group. Comparisons were performed between syndromic variants of LSE and between subgroups of patients with or without paroxysmal activity in their digital EEGs (dEEG). Marked reduction of the energy in the alpha range and a mild increase in the theta range were found in the patients, unrelated to the syndromic variant of the epilepsy. These deviations from normality were widespread on the scalp and were not related to antiepileptic medication. Non-parametric testing showed a positive correlation between the magnitude of the quantitative EEG abnormalities and the amount of paroxysmal activity in the dEEG. Slowing of the mean frequency of alpha components of the spectra, an actual decrease of power in the alpha range and an increase in the theta range explained the results. The most striking finding of this paper is that focal epileptogenesis may have a generalized impact in the frequency composition of EEG.

Adolescent↗

PubMed1995

Frequency source analysis in patients with brain lesions.

In a previous study (Harmony et al. 1993) we observed that the volume of lesions was correlated only with delta power, while the volume and density of edema showed a significant correlation with theta and alpha power, suggesting two independent origins of activity in the delta and theta bands in patients with space-occupying lesions. Our goal in this paper is to show, through a different technique, in a narrow band spectral analysis, that brain lesions are characterized by activity in the delta domain and that edema is better correlated with activity within the theta range. Frequency source analysis based on the Maximum Likelihood (ML) test for rejection of isotropicity was applied to the EEG at rest of 36 patients with space-occupying intracranial lesions. The ML test was rejected at frequencies below 1 Hz and in the low range of the delta rhythm in 31 patients. The origin of the equivalent dipoles at these frequencies was within the volume of the lesion in 27 patients. In 15 patients out of 19 with vasogenic edema the ML test was rejected at frequencies in the theta range. The equivalent dipoles at these frequencies were all within the volume of the edema.

Astrocytoma↗

PubMed1995

Maximum a posteriori estimation of change points in the EEG.

A new approach for EEG segmentation is introduced. This is based on a methodology for optimal segmentation of non-stationary signals derived from the maximum a posteriori estimation principle. It is a model-based, not sequential approach that allows for segmentation at different resolution levels. The features of the methodology are illustrated by its application to EEG recordings containing several types of spectral changes due to normal and pathological variations of spontaneous brain rhythmic activities, as well as physiological artifacts.

Algorithms↗

PubMed1995

EEG predictability: adequacy of non-linear forecasting methods.

The predictive properties of EEG segments were analyzed. The sample included alpha, delta as well as spike and wave EEG activity recordings. Most of these segments are better described with non-linear autoregressive models, and a non-linear forecasting algorithm is routinely required. In terms of their predictive properties, segments can be divided into unpredictable, predictable and very predictable, these three groups being similarly represented among the alpha activity EEG segments. In EEG segments with alpha activity, poor predictability is associated with poor organization of the rhythmic pattern. Concerning dynamic properties, it was found that cyclic skeletons were highly represented among the very predictable segments, which reflect a contribution of the deterministic component of the autoregressive model to the predictability of the segments. Notable contributions of the noise component may explain the properties of unpredictable segments. These results point to a great diversity of predictive patterns among EEG recordings. Other factors besides the existence of chaotic dynamics must be regarded.

Algorithms↗

PubMed1995

Low-dose cyclosporine A improves severe disabling psoriasis in Latin America. Latin American Multicenter Study.

BACKGROUND: Severe forms of psoriasis have been treated successfully with cyclosporine A (cyA) in Europe and North America. The aim of the present investigation was to record and evaluate this drug treatment in Latin American patients with severe psoriasis in a multicenter controlled dose-efficacy study. PATIENTS AND METHODS: One hundred and fifty-two patients from 10 Latin American countries had on entry to the study a Psoriasis Area Severity Index (PASI) of 18 or more. Initial treatment was with cyA, 2.5 mg per kg per day for 6 weeks. At week 6, 27 patients with a baseline PASI score reduction of < 33% had the dose increased to 4 mg/kg/day. At week 12, 48 patients, who had not improved their baseline PASI scores by 66% or more, had their dose increased to 4 or 5 mg/kg/day, respectively. At the end of the study, 74 patients (56%) received cyA 2.5 mg/kg/day, 41 patients (31%) received 4 mg/kg/day, and 16 patients (12%) received 5 mg/kg/day. RESULTS: Cyclosporine A treatment was considered successful in 84.7% of the patients, who reduced their initial PASI score by 66% or more at the end of treatment at week 18. Adverse effects were seen in 29 patients (19%). Hypertension occurred in 27% and an increase of serum creatinine level above 30% of the initial value in 40% of patients. Among other side effects were gastrointestinal complaints (5.1%), hirsutism (4.3%), muscle pain (2.2%), joint pain (2.2%), respiratory infections (2.2%), headache (1.4%), and hemorrhagic gingivitis (0.7%). Twenty-one patients (13.8%) were withdrawn from the study for various reasons: adverse events in five cases (3.3%), noncompliance in five cases (3.3%), lack of efficacy in three cases (2%) and nonrelated diseases in two cases (1.3%). There were also six patients of a group that finished earlier than planned. A follow-up at 8 weeks after treatment was performed in 106 patients; in this phase 60 patients (56.5%) continued with their previous successful PASI reduction. Relapses (i.e., PASI increasing by more than 50% over baseline) were seen in 22.6% of cases. CONCLUSIONS: Cyclosporine A is an effective and well-tolerated treatment for severe psoriasis. An initial dose of 2.5 mg/kg/day is recommended. Most of the patients have a good response to this dose.

Adolescent↗

PubMed1994

Multivariate statistical brain electromagnetic mapping.

Brain Electromagnetic Topography (BET) has attained widespread use. The representation of EEG or MEG parameters as scalp maps (BETm) aids its clinical interpretation. However, some critical issues limit the usefulness of BETm. In particular, the conventional statistical assessment of BETm with respect to normative data is based upon marginal significance probability scales which involve multiple univariate comparisons (one at each recording site). As a consequence, the probability of false positive findings (type I error) is increased above its nominal level. The use of conservative levels avoids this phenomenon but results in a considerable increase of the probability of not detecting real abnormality (type II error). Furthermore, BETm are constructed without taking into consideration the patterns of correlations characteristic of electromagnetic data under normal states of brain functioning. This limits the capability of BETm of representing multivariate aspects of abnormality. This paper introduces some techniques to approach these difficulties. Multivariate Brain Electromagnetic Topographic maps (MBETm) are defined, which retain the attractive features of mapping but also take advantage of multivariate characteristics (in the spatial and frequency domains) to highlight aspects of neuropathology. Moreover, simultaneous significance probability (SSP) scales, valid for both BETm and MBETm, are introduced for the global control of the probability of a type I error. The use of these techniques is illustrated with data from patients with cortical tumours and with epilepsy. ROC analysis shows that in some cases there is a significant improvement in both detection and localization accuracy.

Brain↗

PubMed1994

A global scale factor in brain topography.

In this paper statistical resampling techniques are used to support the presence of an equiangular first principal component in EEG log spectra and therefore the existence of a global scale factor in EEG recordings. the Log transformed spectra from a normal sample (n = 211, age 5-97) were analyzed. To reach this conclusion a method for estimating the scale factor is introduced. It is also shown that this factor remains constant in each individual for all derivations and frequencies and across functional states. The contribution of this scale factor to the overall variance of the normal EEG reaches 42% of the total variance of age corrected data. Part of the variance of the scale factor exhibits age dependency. Scale factor correction of EEG spectra data improves the diagnostic accuracy for detecting pathological EEG spectra from an almost random level (Area under the ROC curve = .6) to .84.

Adolescent↗

PubMed1993

[Plasma estradiol levels and duration of lactation amenorrhea].

In Temuco, Chile, 114 women in fully nursing, were studied, according to their length of lactational amenorrhea and their relation with estradiol levels at 3th postpartum month. Sixty six (58%) recovery their menses before the 6th postpartum month. The length of lactational amenorrhea was 100.7-5.2 and 277 +/- 10.6 days, for those mothers who were with menses and amenorrhea, respectively. The estradiol levels were 88 pmol/l higher in the woman with short length of lactational amenorrhea. This study corroborate, that short length of lactational amenorrhea is a condition highly frequent in Chilean population. The difference in the estradiol levels may be a indicators of the early recovery of the postpartum fertility.

Adolescent↗

PubMed1993

[Advanced endometriosis treatment with leuprolide acetate].

Endometriosis is a disease observed in women in fertile age, it causes pelvic pain characterized by dysmenorrea and dyspareunia. Moreover, there is an association with infertility. Between the alternative of the medical therapeutics of endometriosis drugs with hipogonadotrofic and hypoestrogenic effects, as the danazol and gestrinona has been used. At present, there are analogies of GnRH factor where leuprolide acetate allow a continue liberation in a monthly administration. This is a case of a woman with extensive endometriosis that has hepatitis due to danazol and subsequently was treated with leuprolide acetate. The effectiveness of leuprolide acetate is analyzed in relation with the relief of pain and the laparoscopic evaluation of the endometriosis focus.

Adult↗

PubMed1992

QEEG in a public health system.

For the past decade the Cuban Neuroscience Center has organized on behalf of the Ministry of Public Health of the Republic, a nationwide Program for the introduction of quantitative EEG (qEEG). This Program has involved a) development of standardized equipment for "paperless" EEG, qEEG and brain topography; b) establishment of a network of 21 laboratories of clinical neurophysiology; c) creation of the specialty of clinical neurophysiology which trains physicians from all provinces in both traditional and quantitative electrophysiological methods; d) introduction of standardized protocols for the collection of clinical and electrophysiological information; e) organization of a national normative and neuropsychiatric database; f) establishment of normative regression equations. Among the special issues discussed are: 1) relationship between traditional and quantitative methods; 2) evaluation of the effectiveness of the technology introduced; 3) use of qEEG in the early detection of brain dysfunction.

Adolescent↗

PubMed1992

Frequency domain models of the EEG.

The structure of the normal resting EEG crosspectrum SVV(omega) is analyzed using complex multivariate statistics. Exploratory data analysis with Principal Component Analysis (PCA) is followed by hypothesis testing and computer simulations related to possible neural generators. The SVV(omega) of 211 normal individuals (ages 5 to 97) may be decomposed into two types of processes: the xi process with spatial isotropicity reflecting diffuse, correlated cortical generators with radial symmetry, and processes that seem to be generated by more spatially concentrated, correlated sources. The latter are reflected as spectral peaks such as the process. The eigenvectors of the xi process are the Spherical Harmonic Functions which explains the recurring pattern of maps characteristic of the spatial PCA of qEEG data. A new method for estimating sources in the frequency domain which fits dipoles to the whole crosspectrum is applied to explain the characteristics of the localized sources.

Age Factors↗