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V Cardenas

Publications and source records attributed to V Cardenas.

10 recordsLinked to original sources
PubMed2003

An intensity consistent filtering approach to the analysis of deformation tensor derived maps of brain shape.

Deformation tensor morphometry makes use of the derivatives of spatial transformations between anatomies, to provide highly localized volumetric maps of relative anatomical size. The analysis of such maps, however, has the challenge of describing the data in a way that allows the spatial scale and extent of the local shape properties to match those induced by the disease process being studied. This study examines an approach to the spatial filtering of transformation Jacobian maps created in multisubject studies of brain anatomy, which constrains the filter neighborhood within common structural boundaries present in the spatially normalized image data. The filtering incorporates information derived from the spatial normalization process, using a statistical framework to introduce a measure of uncertainty in local regional intensity correspondence following spatial normalisation. The proposed filtering approach is compared to the use of spatially invariant Gaussian filtering in the analysis of Jacobian determinant maps of brain shape and shape change in Alzheimer's disease and normal aging. Results show significantly improved delineation of fine scale patterns of shape difference (in cross-sectional studies) and shape change (from multiple serial magnetic resonance imaging studies).

Age Factors↗
PubMed2001

Introduction of the new Centers for Disease Control and Prevention group B streptococcal prevention guideline at a large West Coast health maintenance organization.

OBJECTIVE: Our purpose was to assess the impact of new consensus guidelines issued by the Centers for Disease Control and Prevention, The American College of Obstetricians and Gynecologists, and the American Academy of Pediatrics to prevent perinatal group B streptococcal disease. STUDY DESIGN: We performed a descriptive analysis and a before-and-after analysis of implementation of the group B streptococcal disease prevention guidelines among singleton-birth pregnancies in 2 Group Health Cooperative hospitals from October 1, 1995, through December 31, 1997. We studied the speed and completeness of implementation and the effect on pregnancy care practices including intrapartum antibiotic use, test ordering, and maternal and neonatal health. RESULTS: Guideline implementation occurred rapidly. The proportion of term pregnancies screened according to the guideline increased markedly, and overall intrapartum antibiotic use more than doubled. Among group B streptococci-positive women, intrapartum antibiotic prophylaxis increased from 24% before to 74% after guideline implementation. Median duration of treatment before delivery increased from 1.8 to 4.3 hours. The rate of rash did not increase, and there were no cases of anaphylaxis or pseudomembranous colitis. The proportion of infants undergoing evaluation decreased after implementation of the neonatal guidelines; among infants of group B streptococci-negative women, test ordering dropped by almost 40%. CONCLUSIONS: Implementation of the new guidelines is feasible and can be accomplished rapidly. The guidelines were associated with increased maternal intrapartum antibiotic use, particularly among women at highest risk, and with a decrease in laboratory use for infants.

Adult↗
PubMed2000

Hippocampal and cortical atrophy predict dementia in subcortical ischemic vascular disease.

BACKGROUND: The cause of dementia in subcortical ischemic vascular disease (SIVD) is controversial. OBJECTIVES: To determine whether cognitive impairment in SIVD 1) correlates with measures of ischemic brain injury or brain atrophy, and/or 2) is due to concomitant AD. METHODS: Volumetric MRI of the brain was performed in 1) elderly subjects with lacunes (L) and a spectrum of cognitive impairment-normal cognition (NC+L, n = 32), mild cognitive impairment (CI+L, n = 26), and dementia (D+L, n = 29); 2) a comparison group with probable AD (n = 28); and 3) a control group with normal cognition and no lacunes (NC). The authors examined the relationship between the severity of cognitive impairment and 1) volume, number, and location of lacunes; 2) volume of white matter signal hyperintensities (WMSH); and 3) measures of brain atrophy (i. e., hippocampal, cortical gray matter, and CSF volumes). RESULTS: Among the three lacune groups, severity of cognitive impairment correlated with atrophy of the hippocampus and cortical gray matter, but not with any lacune measure. Although hippocampal atrophy was the best predictor of severity of cognitive impairment, there was evidence for a second, partially independent, atrophic process associated with ventricular dilation, cortical gray matter atrophy, and increase in WMSH. Eight autopsied SIVD cases showed variable severity of ischemic and neurofibrillary degeneration in the hippocampus, but no significant AD pathology in neocortex. The probable AD group gave evidence of only one atrophic process, reflected in the severity of hippocampal atrophy. Comparison of regional neocortical gray matter volumes showed sparing of the primary motor and visual cortices in the probable AD group, but relatively uniform atrophy in the D+L group. CONCLUSIONS: Dementia in SIVD, as in AD, correlates best with hippocampal and cortical atrophy, rather than any measure of lacunes. In SIVD, unlike AD, there is evidence for partial independence between these two atrophic processes. Hippocampal atrophy may result from a mixture of ischemic and degenerative pathologies. The cause of diffuse cortical atrophy is not known, but may be partially indexed by the severity of WMSH.

Aged↗
PubMed1999

Elevated subcortical choline metabolites in cognitively and clinically asymptomatic HIV+ patients.

OBJECTIVE: To determine whether the concentrations of the neuronal marker N-acetylaspartate (NAA) and the choline-containing metabolites (Cho) are altered in the subcortical brain of HIV+ patients who are cognitively normal and clinically asymptomatic, and to determine whether these alterations are greater in the presence of cognitive impairments and clinical symptoms. BACKGROUND: Pathologic studies suggest that subcortical gray matter carries a heavy HIV load, and neuropsychological test results are consistent with involvement of subcortical and frontostriatal brain systems in HIV disease. Noninvasive proton magnetic resonance spectroscopy (1H MRS) suggests neuronal preservation and macrophage infiltration in the subcortical brain of clinically symptomatic and cognitively impaired HIV+ individuals. Improved 1H MRS methods may allow the early detection of metabolite alterations in the subcortical brain of asymptomatic HIV+ individuals. METHODS: Two-dimensional 1H MRS imaging was performed on 30 HIV- control subjects and 70 HIV+ patients with varying severities of systemic disease and neuropsychological impairments, but without cerebral opportunistic infections. RESULTS: Subcortical Cho was elevated in HIV+ patients compared with control subjects regardless of the presence or absence of cognitive impairment or clinical symptoms. Subcortical NAA was lower than control NAA only in severely cognitively impaired HIV+ subjects. Subcortical NAA correlated with performance on a variety of neuropsychological tests but not with Centers for Disease Control clinical stage, whereas high-thalamic Cho was associated with low CD4 lymphocyte counts. CONCLUSIONS: 1H MRS imaging detects higher Cho in subcortical brain early in HIV disease, when individuals are clinically and neuropsychologically asymptomatic, whereas lower NAA is only found in subcortical brain in individuals with severe neuropsychological impairments. Quantitative 1H MRS imaging may play a role in the objective assessment of the presence, magnitude, and progression of brain involvement in HIV infection.

Adult↗
PubMed1998

Hyperendemic pulmonary tuberculosis in a Peruvian shantytown.

Estimates of the incidence of pulmonary tuberculosis in developing countries are based on case reporting from local health laboratories or the annual risk of tuberculin skin test conversion. Because these methods are problematic, the authors used a multiple case ascertainment method to estimate the incidence of pulmonary tuberculosis from 1989 to 1993 in a Peruvian shantytown of 34,000 inhabitants. Two methods, face-to-face interview of all local inhabitants and examination of local laboratory smear records, were used for case gathering. The number of missed cases was estimated by capture-recapture analysis. Survey cases with positive smears were matched to age- and sex-matched controls and interviewed about socioeconomic conditions. The average annual incidence per 100,000 population was 364 (95% confidence interval 293-528) by capture-recapture methods. For the city encompassing the shantytown, the Peruvian Ministry of Heath reported an average annual incidence of 134 cases per 100,000 population. The authors conclude that, in Peru, alarming clusters of pulmonary tuberculosis are masked by government reports that pool zones of disparate incidence. Existing estimators of pulmonary tuberculosis incidence based on tuberculin conversion rates may be invalid in such areas. Within these hyperendemic areas, persons suitable for intensive prophylaxis efforts cannot be reliably identified by housing and socioeconomic risk factors.

Adult↗
PubMed1998

Partial liquid ventilation in adult patients with ARDS: a multicenter phase I-II trial. Adult PLV Study Group.

OBJECTIVE: To evaluate the safety and efficacy of partial liquid ventilation (PLV) in adult patients with the acute respiratory distress syndrome (ARDS). SUMMARY BACKGROUND DATA: Previous studies have evaluated gas exchange and the safety of PLV in adult patients with severe respiratory failure whose gas exchange was partially provided by extracorporeal life support (ECLS). This is the first experience with adult patients who were not on ECLS. METHODS: Intratracheal perflubron in a total dose of 30.1 +/- 7.1 ml/kg was administered over a period of 45 +/- 9 hours to nine adult patients with mean age = 49 +/- 4 years and mean PaO2/FiO2 ratio = 128 +/- 7 as part of a prospective, multicenter, phase I-II noncontrolled trial. RESULTS: Significant decreases in mean (A-a)DO2 (baseline = 430 +/- 47, 48 hour = 229 +/- 17, p = 0.0127 by ANOVA) and FiO2 (baseline = 0.82 +/- 0.08, 48 hour = 0.54 +/- 0.06, p = 0.025), along with an increase in mean SvO2 (baseline = 75 +/- 3, 48 hour = 85 +/- 2, p = 0.018 by ANOVA) were observed. No significant changes in pulmonary compliance or hemodynamic variables were noted. Seven of the nine patients in this study survived beyond 28 days after initiation of partial liquid ventilation whereas 5 patients survived to discharge. Three adverse events [hypoxia (2) and hyperbilirubinemia (1)] were determined to be severe in nature. CONCLUSIONS: These data suggest that PLV may be performed safely with few related severe adverse effects. Improvement in gas exchange was observed in this series of adult patients over the 48 hours after initiation of PLV.

Adult↗
PubMed1998

Kinetics of CO2 excretion and intravascular pH disequilibria during carbonic anhydrase inhibition.

Inhibition of carbonic anhydrase (CA) activity (activity in red blood cells and activity available on capillary endothelium) results in decrements in CO2 excretion (VCO2) and plasma-erythrocyte CO2-HCO(-3)-H+ disequilibrium as blood travels around the circulation. To investigate the kinetics of changes in blood PCO2 and pH during progressive CA inhibition, we used our previously detailed mathematical model of capillary gas exchange to analyze experimental data of VCO2 and blood-gas/pH parameters obtained from anesthetized, paralyzed, and mechanically ventilated dogs after treatment with acetazolamide (Actz, 0-100 mg/kg i.v.). Arterial and mixed venous blood samples were collected via indwelling femoral and pulmonary arterial catheters, respectively. Cardiac output was measured by thermodilution. End-tidal PCO2, as a measure of alveolar PCO2, was obtained from continuous records of airway PCO2 above the carina. Experimental results were analyzed with the aid of a mathematical model of lung and tissue-gas exchange. Progressive CA inhibition was associated with stepwise increments in the equilibrated mixed venous-alveolar PCO2 gradient (9, 19, and 26 Torr at 5, 20, and 100 mg/kg Actz, respectively). The maximum decrements in VCO2 were 10, 24, and 26% with 5, 20, and 100 mg/kg Actz, respectively, without full recovery of VCO2 at 1 h postinfusion. Equilibrated arterial PCO2 overestimated alveolar PCO2, and tissue PCO2 was underestimated by the measured equilibrated mixed venous blood PCO2. Mathematical model computations predicted hysteresis loops of the instantaneous CO2-HCO(-3)-H+ relationship and in vivo blood PCO2-pH relationship due to the finite reaction times for CO2-HCO(-3)-H+ reactions. The shape of the hysteresis loops was affected by the extent of Actz inhibition of CA in red blood cells and plasma.

Acetazolamide↗
PubMed1995

Frequency domain estimation of covariate effects in multichannel brain evoked potential data.

An evoked potential is the recorded brain electrical response to a stimulus such as an auditory click. In most evoked potential experiments, the response is studied as a function of covariates such as stimulus characteristics and drug states. We propose a frequency domain model of multichannel evoked potential data that includes parameters representing the effects of covariates on the amplitude and latency (time from stimulus presentation) of the response. The variability of the response among scalp electrodes is modeled by the activity of one or more equivalent electrical dipoles. The frequency domain representation allows considerable data reduction, facilitates modeling of the noise, and leads to a simple approximate expression for the latency effects. We describe maximum likelihood estimation of the model parameters and construction of approximate confidence intervals for the covariate effects. We report the results of a simulation study in which we evaluated the bias of the estimators and the coverage rate of the confidence intervals. We also report the results of an application to auditory evoked potentials recorded from five subjects.

Algorithms↗