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At least 217 records · Page 12Linked to original sources

PubMed2005

Oxygen saturation regularity analysis in the diagnosis of obstructive sleep apnea.

OBJECTIVE: The present study assessed the validity of approximate entropy (ApEn) analysis of arterial oxygen saturation (SaO(2)) data obtained from pulse oximetric recordings as a diagnostic test for obstructive sleep apnea (OSA) in patients clinically suspected of suffering this disease. METHODOLOGY: A sample of 187 referred outpatients, clinically suspected of having OSA, was studied using nocturnal pulse oximetric recording performed simultaneously with complete polysomnography. ApEn analysis was applied to SaO(2) data. RESULTS: Patients with OSA presented significantly higher approximate entropy levels than those without OSA (1.08+/-0.30 versus 0.47+/-0.26). Apnea-hypopnea index was correlated significantly with ApEn (r=0.607; p<0.001). Using receiver operating characteristic curve analysis, we obtained a diagnostic sensitivity of 88.3% and specificity of 82.9%, positive predictive value of 88.3% and a negative predictive value of 82.9%, at a threshold of 0.679. As a diagnostic test, this method presents high sensitivity and specificity compared to traditional methods in the diagnosis of OSA. CONCLUSION: We conclude that ApEn analysis of SaO(2) data obtained from pulse oximetric recordings could be useful as a diagnostic technique for OSA subjects.

Adult↗

PubMedDate not supplied

Chemical library subset selection algorithms: a unified derivation using spatial statistics.

If similar compounds have similar activity, rational subset selection becomes superior to random selection in screening for pharmacological lead discovery programs. Traditional approaches to this experimental design problem fall into two classes: (i) a linear or quadratic response function is assumed (ii) some space filling criterion is optimized. The assumptions underlying the first approach are clear but not always defendable; the second approach yields more intuitive designs but lacks a clear theoretical foundation. We model activity in a bioassay as realization of a stochastic process and use the best linear unbiased estimator to construct spatial sampling designs that optimize the integrated mean square prediction error, the maximum mean square prediction error, or the entropy. We argue that our approach constitutes a unifying framework encompassing most proposed techniques as limiting cases and sheds light on their underlying assumptions. In particular, vector quantization is obtained, in dimensions up to eight, in the limiting case of very smooth response surfaces for the integrated mean square error criterion. Closest packing is obtained for very rough surfaces under the integrated mean square error and entropy criteria. We suggest to use either the integrated mean square prediction error or the entropy as optimization criteria rather than approximations thereof and propose a scheme for direct iterative minimization of the integrated mean square prediction error. Finally, we discuss how the quality of chemical descriptors manifests itself and clarify the assumptions underlying the selection of diverse or representative subsets.

Journal Article↗

PubMed2005

Role of angular momentum conservation in unimolecular translational energy release: validity of the orbiting transition state theory.

The translational kinetic energy release distribution (KERD) for the halogen loss reaction of the bromobenzene and iodobenzene cations has been reinvestigated on the microsecond time scale. Two necessary conditions of validity of the orbiting transition state theory (OTST) for the calculation of kinetic energy release distributions (KERDs) have been formulated. One of them examines the central ion-induced dipole potential approximation. As a second criterion, an adiabatic parameter is derived. The lower the released translational energy and the total angular momentum, the larger the reduced mass, the rotational constant of the molecular fragment, and the polarizability of the released atom, the more valid is the OTST. Only the low-energy dissociation of the iodobenzene ion (E approximately 0.45 eV, where E is the internal energy above the reaction threshold) is found to fulfill the criteria of validity of the OTST. The constraints that act on the dissociation dynamics have been studied by the maximum entropy method. Calculations of entropy deficiencies (which measure the deviation from a microcanonical distribution) show that the pair of fragments does not sample the whole of the phase space that is compatible with the mere specification of the internal energy. The major constraint that results from conservation of angular momentum is related to a reduction of the dimensionality of the dynamics of the translational motion to a two-dimensional space. A second and minor constraint that affects the KERD leads to a suppression of small translational releases, i.e., accounts for threshold behavior. At high internal energies, the effects of curvature of the reaction path and of angular momentum conservation are intricately intermeddled and it is not possible to specify the share of each effect.

Journal Article↗

PubMed1994

Overcoming non-isomorphism by phase permutation and likelihood scoring: solution of the TrpRS crystal structure.

Entropy maximization to maximum likelihood, constrained jointly by the best available experimental phases and by a sufficiently good envelope, can bring about substantial model-independent map improvement, even at medium (3.1 A) resolution [Xiang, Carter, Bricogne & Gilmore (1993). Acta Cryst. D49, 193-212]. In the crystal structure determination of the Bacillus stearothermophilus tryptophanyl-tRNA synthetase (TrpRS), however, the following had to be dealt with simultaneously: (1) a serious lack of isomorphism in the heavy-atom derivatives, resulting in large starting-phase errors; and (2) an initially poorly known molecular envelope. Because the constraints--both phases and envelope--were insufficiently well determined at the outset, maximum-entropy solvent flattening as previously applied was unsuccessful. Rather than improving the maps, it led to a deterioration of their quality, accompanied by a dramatic decrease of the log-likelihood gain as phases were extended from about 5 A resolution to the 2.9 A limit of the diffraction data. This deadlock was broken by the identification of strong reflections, which were initially unphased and which were inaccessible by maximum-entropy extrapolation from the phased ones, and by permutation of the phases of these reflections so as to sample the space of possible electron-density and envelope modifications they represented. Permutation was carried out by successive full and incomplete factorial designs [Carter & Carter (1979). J. Biol. Chem. 254, 12219-12223] for 28 strong reflections selected in decreasing order of their 'renormalized' structure-factor amplitudes. The permuted reflections included one reflection for which the probability distribution from multiple isomorphous replacement with anomalous scattering (MIRAS) indicated an incorrect phase with a high figure of merit and which consequently had a large renormalized structure factor. A similar permutation was carried out for six different binary choices related to the calculation and description of the molecular envelope. Permutation experiments were scored using the log-likelihood gain and contrasts for each main effect were analyzed by multiple-regression least squares. Student t tests provided significant and reliable indications for a large majority of the permuted reflections and for all six hypotheses related to the molecular envelope. The resulting phase improvement made it possible to assign positions (hitherto unobtainable) for nine of the ten selenium atoms in an isomorphous difference Fourier map for selenomethionine-substituted TrpRS crystals and hence to solve the structure. Phase-permutation methods continued to be useful in producing improved maps from all the available isomorphous-replacement phase information and therefore played a critical role in solving the structure.(ABSTRACT TRUNCATED AT 400 WORDS)

Bayes Theorem↗

PubMed1995

An extensive Markov system for ECG exact coding.

In this paper, an extensive Markov process, which considers both the coding redundancy and the intersample redundancy, is presented to measure the entropy value of an ECG signal more accurately. It utilizes the intersample correlations by predicting the incoming n samples based on the previous m samples which constitute an extensive Markov process state. Theories of the extensive Markov process and conventional n repeated applications of m-th order Markov process are studied first in this paper. After that, they are realized for ECG exact coding. Results show that a better performance can be achieved by our system. The average code length for the extensive Markov system on the second difference signals was 2.512 b/sample, while the average Huffman code length for the second difference signals was 3.326 b/sample.

Electrocardiography↗

PubMed2004

Experimentally induced androgen depletion accentuates ethnicity-related contrasts in luteinizing hormone secretion in asian and caucasian men.

The basis for ethnicity-related distinctions in gonadotropin secretion are unknown but may have important populational and physiological implications. In male contraceptive trials, exogenous testosterone and progestins suppress spermatogenesis to a greater degree in Asian than Caucasian men. In addition, iv infusion of testosterone inhibits LH release more in Asian than Caucasian volunteers. We test the converse postulate that experimental reduction of androgen-dependent negative feedback by way of the steroidogenic inhibitor combination ketoconazole/dexamethasone will unveil ethnicity-related mechanisms of regulated LH secretion in young men. LH release was monitored by sampling blood every 10 min for 24 h followed by immunoradiometric assay, model-free pulse detection, an entropy (regulatory) statistic, and cosine regression. Statistical comparisons revealed that healthy young Asian and Caucasian men maintain comparable baseline concentrations of LH, testosterone, estradiol, SHBG, and molar testosterone to SHBG ratios. In contrast, the two ethnic groups differ prominently in each of basal, pulsatile, entropic, and 24-h rhythmic LH adaptations to short-term androgen withdrawal. Therefore, we postulate that physiological nonuniformity of sex steroid-dependent negative feedback in particular may contribute to populational diversity in LH regulation.

Adaptation, Physiological↗

PubMed2004

Paroxetine decreases respiratory irregularity of linear and nonlinear measures of respiration in patients with panic disorder. A preliminary report.

Previous studies indicate that serotonin reuptake inhibitors do not appear to have serious cardiac side effects. However, the effects of these agents on respiratory measures have not been studied in detail. Several studies indicate that patients with anxiety exhibit irregular breathing patterns as measured by tidal volume and respiratory rate. In this study, we evaluated the effects of a serotonin reuptake inhibitor, paroxetine, on respiratory variability in patients with panic disorder (n = 13), using linear and nonlinear measures of regularity, approximate entropy (APEN) and a measure of chaos, the largest Lyapunov exponent (LLE), with pre- and posttreatment lung volume time series (256 s long sampled at 4 Hz). Our results show that paroxetine significantly decreases some of the linear measures of variability and supine APEN and standing LLE of lung volume series after successful treatment. The implications of these findings on respiratory and cardiovascular function have been discussed.

Adult↗

PubMed2003

A new & robust information theoretic measure and its application to image alignment.

In this paper we develop a novel measure of information in a random variable based on its cumulative distribution that we dub cumulative residual entropy (CRE). This measure parallels the well known Shannon entropy but has the following advantages: (1) it is more general than the Shannon Entropy as its definition is valid in the discrete and continuous domains, (2) it possess more general mathematical properties and (3) it can be easily computed from sample data and these computations asymptotically converge to the true values. Based on CRE, we define the cross-CRE (CCRE) between two random variables, and apply it to solve the image alignment problem for parameterized (3D rigid and affine) transformations. The key strengths of the CCRE over using the mutual information (based on Shannon's entropy) are that the former has significantly larger tolerance to noise and a much larger convergence range over the field of parameterized transformations. We demonstrate these strengths via experiments on synthesized and real image data.

Algorithms↗

PubMed2002

Entropy and complexity of finite sequences as fluctuating quantities.

The paper is devoted to the analysis of digitized sequences of real numbers and discrete strings, by means of the concepts of entropy and complexity. Special attention is paid to the random character of these quantities and their fluctuation spectrum. As applications, we discuss neural spike-trains and DNA sequences. We consider a given sequence as one realization of finite length of certain random process. The other members of the ensemble are defined by appropriate surrogate sequences and surrogate processes. We show that n-gram entropies and the context-free grammatical complexity have to be considered as fluctuating quantities and study the corresponding distributions. Different complexity measures reveal different aspects of a sequence. Finally, we show that the diversity of the entropy (that takes small values for pseudorandom strings) and the context-free grammatical complexity (which takes large values for pseudorandom strings) give, nonetheless, consistent results by comparison of the ranking of sample sequences taken from molecular biology, neuroscience, and artificial control sequences.

Action Potentials↗

PubMed2007

Disconnect in concept learning by rhesus monkeys (Macaca mulatta): judgment of relations and relations-between-relations.

The authors investigated the role that entropy measures, discriminative cues, and symbolic knowledge play for rhesus monkeys (Macaca mulatta) in the acquisition of the concepts of same and different for use in a computerized relational matching-to-sample task. After repeatedly failing to perceive relations between pairs of stimuli in a 2-choice discrimination paradigm, monkeys rapidly learned to discriminate between 8-element arrays. Subsequent tests with smaller arrays, however, suggested that, although important for the initial acquisition of the concept, entropy is not a variable on which monkeys are dependent. Not only do monkeys choose a corresponding relational pair in the presence of a cue, but they also choose the cue itself in the presence of the relational pair--in essence, labeling those relations. Subsequent failure in the judgment of relations-between-relations, however, suggests that perhaps a qualitatively different cognitive component exists that prevents monkeys from behaving analogically.

Animals↗

PubMed1998

Pituitary apoplexy in acromegaly, a long-term follow-up study in two patients.

Pituitary apoplexy is a serious complication in about 3% of patients with a pituitary adenoma. Very often, the diagnosis of a functioning or non-functioning adenoma is made in retrospect. In this report, we describe two patients in whom the diagnosis of acromegaly was made before the apoplexy. In one patient, surgical intervention was necessary because of remaining clinical and biochemical activity; in the other patient conservative follow-up was pursued. Seven and nine years after apoplexy, respectively, the patients were clinically and biochemically in remission. During the follow-up, three and five years after apoplexy, respectively, the patients underwent a 10-min venous sampling procedure for 24 hours, and the GH secretory profile was investigated with multiparameter deconvolution analysis and by approximate entropy (ApEn), a scale- and model-independent regularity measure. The deconvolution analysis revealed an increased basal (nonpulsatile) GH secretion rate, while the total 24 h secretion rate was normal compared with 13 healthy male control subjects. ApEn was much larger for each patient than for any control subject value, indicating markedly more irregular GH secretion. We hypothesize that these subtle abnormalities are caused by non-specific damage as a result of vascular insult, leading to abnormal vascular supply, or abnormal autocrine and paracrine GH regulation within the remaining gland.

Acromegaly↗

PubMed1998

Pressure effects on the lateral distribution of cholesterol in lipid bilayers: a time-resolved spectroscopy study.

The effects of hydrostatic pressure and temperature on the phase behavior and physical properties of the binary mixture palmitoyloleoylphosphatidylcholine/cholesterol, over the 0-40 molar % range of cholesterol compositions, were determined from the changes in the fluorescence lifetime distribution and anisotropy decay parameters of the natural lipid trans-parinaric acid (t-PnA). Pressurized samples were excited with a Ti-sapphire subpicosecond laser, and fluorescence decays were analyzed by the quantified maximum entropy method. Above the transition temperature (T(T) = -5 degrees C), at atmospheric pressure, two liquid-crystalline phases, alpha and beta, are formed in this system. At each temperature and cholesterol concentration below the transition pressure, the fluorescence lifetime distribution pattern of t-PnA was clearly modulated by the pressure changes. Pressure increased the fraction of the liquid-ordered beta-phase and its order parameter, but it decreased the amount of cholesterol in this phase. Palmitoyloleoylphosphatidylcholine/cholesterol phase diagrams were also determined as a function of temperature and hydrostatic pressure.

Biophysical Phenomena↗

PubMed1996

Older males secrete luteinizing hormone and testosterone more irregularly, and jointly more asynchronously, than younger males.

New statistical perspectives on the secretory patterns of both luteinizing hormone (LH) and testosterone (T) may prove useful in further understanding the aging process, and possibly ultimately in improving the diagnosis and treatment of spermatogenetic failure and loss of sexual interest. We examined serum concentration time-series for LH and T in 14 young (21-34 years of age) and 11 aged (62-74 years of age) healthy men. For each subject, blood samples were obtained at 2.5-min intervals during a sleep period, with an average sampling duration of 7 hr. For each of LH and T, we used the model-independent statistic approximate entropy (ApEn) to quantify the irregularity of the serum concentration time-series; to quantify joint LH-T secretory asynchrony, we employed the recently introduced cross-ApEn. Although mean (and SD) LH and T concentrations were indistinguishable in the two age groups (P > 0.25), for LH, aged subjects had greater ApEn values (1.525 +/- 0.221) than younger individuals (1.207 +/- 0.252), P < 0.003, indicating more irregular secretion in the older cohort. For T, aged subjects also had greater ApEn values (1.622 +/- 0.120) than younger counterparts (1.384 +/- 0.228), P < 0.004. In young, but not older men, ApEn(T) significantly exceeded ApEn(LH), P < 0.02. Aged subjects had greater cross-ApEn values (1.961 +/- 0.121) than younger subjects (1.574 +/- 0.249), P < 10(-4), with nearly 100% sensitivity and specificity, indicating greater LH-T asynchrony in the older group. In conjunction with previous findings of greater irregularity of growth hormone release with increasing age, we propose that increased secretory irregularity with advancing age may be a widespread hormonal phenomenon. Finally, theoretically, we clarify the need for quantifications such as ApEn and cross-ApEn via a study of a "variable lag" pulsatile process, and empirically note the potential wide applicability of cross-ApEn to quantify asynchrony in interconnected (hormonal) networks.

Adult↗

PubMed2002

Fractal analysis in the detection of colonic cancer images.

The aim of this study was to investigate the value of fractal dimension in separating normal and cancerous images, and to examine the relationship between fractal dimension and traditional texture analysis features. Forty-four normal images and 58 cancer images from sections of the colon were analyzed. A "leave-one-out" analysis approach was used to classify the samples into each group. With fractal analysis there was a highly significant difference between groups (p < 0.0001). Correlation and entropy features showed greater differences between the groups (p < 0.0001). Nevertheless, the addition of fractal analysis to the feature analysis improved the sensitivity from 90% to 95% and specificity from 86% to 93%.

Case-Control Studies↗

PubMed2005

Nutritional, functional, and emotional characteristics related to fatigue in patients during and after biochemotherapy.

PURPOSE/OBJECTIVES: To test Winningham's psychobiologic entropy hypothesis in patients receiving biochemotherapy for melanoma. DESIGN: Descriptive, correlational, cross-sectional study. SETTING: Midwest cancer center. SAMPLE: 25 male and female patients who were receiving biochemotherapy or who had completed treatment 6-12 months prior. METHODS: Data were collected using a series of questionnaires and diet recall. MAIN RESEARCH VARIABLES: Fatigue, anxiety, depression, distressing symptoms, nutritional intake, and weight. FINDINGS: Moderate fatigue was significantly related to physiologic and psychological symptoms but not to nutrient intake. The sample was overweight, and a significant number of participants were obese. High caloric intakes were evident. Depression was a significant problem. CONCLUSIONS: Fatigue was not as severe as expected, but problems with responses to the fatigue scale may explain this. Nutritional status and nutrient intake were not correlated to fatigue in this sample. Activity levels were related to fatigue, and treatment reduced activity. On average, activity returned to pretreatment levels 6-12 months after treatment. Winningham's hypothesis held and will be useful for understanding fatigue in this population. IMPLICATIONS FOR NURSING: Depression needs to be assessed and treated as a side effect of biotherapy. Assessing the impact of nutrition when patients are overweight or obese is difficult. A scale specifically designed to test Winningham's hypothesis is needed.

Adult↗

PubMed2005

Profiling cytogenetic diversity with entropy-based karyotypic analysis.

Regardless the high degree of variation observed in solid tumor karyotypes, the use of diversity as a measurable phenomenon remains unexplored. Here we present a systematic cytogenetic analysis using Shannon's entropy as a measure for karyotypic diversity. Karyotypes from 14 epithelial tumor types (n = 1232) have the aneuploidy status scored, resulting in highly asymmetrical sample distribution, for which we determine the index of diversity (Shannon H') of structural and numerical chromosomal aberrations. Since karyotypic diversity is tissue-specific, this approach may give rise to new insights into the processes that may account for aneuploidy progression and solid tumor outcomes.

Chromosome Aberrations↗

PubMed2006

Low-temperature heat capacity of room-temperature ionic liquid, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

Heat capacities of liquid, stable crystal, and liquid-quenched glass of a room-temperature ionic liquid (RTIL), 1-hexyl-3-methylimidazolium bis(trifluromethylsulfonyl)imide were measured between 5 and 310 K by adiabatic calorimetry. Heat capacity of the liquid at 298.15 K was determined for an IUPAC project as (631.6 +/- 0.5) J K(-1) mol(-1). Fusion was observed at T(fus) = 272.10 K for the stable crystalline phase, with enthalpy and entropy of fusion of 28.34 kJ mol(-1) and 104.2 J K(-1) mol(-1), respectively. The purity of the sample was estimated as 99.83 mol % by the fractional melting method. The liquid could be supercooled easily and the glass transition was observed around T(g) approximately 183 K, which was in agreement with the empirical relation, T(g) approximately ((2)/(3)) T(fus). The heat capacity of the liquid-quenched glass was larger than that of the crystal as a whole. In the lowest temperature region, however, the difference between the two showed a maximum around 6 K and a minimum around 15 K, at which the heat capacity of the glass was a little smaller than that of crystal.

Imidazoles↗

PubMed2003

Estimation of entropies and dimensions by nonlinear symbolic time series analysis.

Symbolic nonlinear time series analysis methods have the potential for analyzing nonlinear data efficiently with low sensitivity to noise. In symbolic nonlinear time series analysis a time series for a fixed delay is partitioned into a small number (called the alphabet size) of cells labeled by symbols, creating a symbolic time series. Symbolic methods involve computing the statistics of words made from the symbolic time series. Specifically, the Shannon entropy of the distribution of possible words for a range of word lengths is computed. The rate of increase of the entropy with word length is the metric (Kolmogorov-Sinai) entropy. Methods of computing the metric entropy for flows as well as for maps are shown. A method of computing the information dimension appropriate to symbolic analysis is proposed. In terms of this formulation, the information dimension is determined by the scaling of entropy as alphabet size is modestly increased, using the information obtained from large word length. We discuss the role of sampling time and the issue of using these methods when there may be no generating partition.

Journal Article↗