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PubMed2001

Assessing serial irregularity and its implications for health.

Approximate entropy (ApEn) is a recently formulated family of parameters and statistics quantifying regularity (orderliness) in serial data, with developments within theoretical mathematics as well as numerous applications to multiple biological contexts. We discuss the motivation for ApEn development, from the study of inappropriate application of dynamical systems (complexity) algorithms to general time-series settings. ApEn is scale invariant and model independent, evaluates both dominant and subordinant patterns in data, and discriminates series for which clear feature recognition is difficult. ApEn is applicable to systems with at least 50 data points and to broad classes of models: it can be applied to discriminate both general classes of correlated stochastic processes, as well as noisy deterministic systems. Moreover, ApEn is complementary to spectral and autocorrelation analyses, providing effective discriminatory capability in instances in which the aforementioned measures exhibit minimal distinctions. Representative ApEn applications to human aging studies, based on both heart rate and endocrinologic (hormonal secretory) time series, are featured. Heart rate (HR) studies include gender- and age-related changes in HR dynamics in older subjects, and analyses of "near-SIDS" infants. Endocrinologic applications establish clear quantitative changes in joint LH-testosterone secretory dynamics in older versus younger men (a "partial male menopause"), via cross-ApEn, a related two-variable asynchrony formulation; a disruption in LH-FSH-NPT (penile tumescence) synchrony in older subjects; and changes in LH-FSH secretory dynamics across menopause. The capability of ApEn to assess relatively subtle disruptions, typically found earlier in the history of a subject than mean and variance changes, holds the potential for enhanced preventative and earlier interventionist strategies.

Algorithms↗

PubMed2003

The dynamic neural filter: a binary model of spatiotemporal coding.

We describe and discuss the properties of a binary neural network that can serve as a dynamic neural filter (DNF), which maps regions of input space into spatiotemporal sequences of neuronal activity. Both deterministic and stochastic dynamics are studied, allowing the investigation of the stability of spatiotemporal sequences under noisy conditions. We define a measure of the coding capacity of a DNF and develop an algorithm for constructing a DNF that can serve as a source of given codes. On the basis of this algorithm, we suggest using a minimal DNF capable of generating observed sequences as a measure of complexity of spatiotemporal data. This measure is applied to experimental observations in the locust olfactory system, whose reverberating local field potential provides a natural temporal scale allowing the use of a binary DNF. For random synaptic matrices, a DNF can generate very large cycles, thus becoming an efficient tool for producing spatiotemporal codes. The latter can be stabilized by applying to the parameters of the DNF a learning algorithm with suitable margins.

Algorithms↗

PubMed2000

Bayesian identification of a population compartmental model of C-peptide kinetics.

When models are used to measure or predict physiological variables and parameters in a given individual, the experiments needed are often complex and costly. A valuable solution for improving their cost effectiveness is represented by population models. A widely used population model in insulin secretion studies is the one proposed by Van Cauter et al. (Diabetes 41:368-377, 1992), which determines the parameters of the two compartment model of C-peptide kinetics in a given individual from the knowledge of his/her age, sex, body surface area, and health condition (i.e., normal, obese, diabetic). This population model was identified from the data of a large training set (more than 200 subjects) via a deterministic approach. This approach, while sound in terms of providing a point estimate of C-peptide kinetic parameters in a given individual, does not provide a measure of their precision. In this paper, by employing the same training set of Van Cauter et al., we show that the identification of the population model into a Bayesian framework (by using Markov chain Monte Carlo) allows, at the individual level, the estimation of point values of the C-peptide kinetic parameters together with their precision. A successful application of the methodology is illustrated in the estimation of C-peptide kinetic parameters of seven subjects (not belonging to the training set used for the identification of the population model) for which reference values were available thanks to an independent identification experiment.

Adult↗

PubMed2000

Efficiency in provision of public dental services in Norway.

The paper examines productivity in the provision of public dental services in Norway. The main responsibility of the public dental services is to provide care for all children up to 18 years of age. Most dental care is provided by public dental officers. Productivity was measured by estimating a stochastic production frontier from input and output data from the public dental service in Norway. The results indicate that there are increasing returns to scale. Our measure of technical efficiency showed that the level of inefficiency is fairly small. However, the inefficiency is greater when estimated from a deterministic production frontier rather than from a stochastic frontier. One limitation of the present methodology is that it does not say anything about the level of efficiency in the Norwegian public dental service in absolute terms. A greater level of inefficiency would have been identified if a few counties had performed clearly better than the rest.

Adolescent↗

PubMed2003

Evaluation of patient and staff doses during various CT fluoroscopy guided interventions.

As CT scanners are more routinely used as a guidance tool for various types of interventional radiological procedures, concern has grown for high patient and staff doses. CT fluoroscopy provides the physician immediate feedback and can be a valuable tool to dynamically assist various types of percutaneous interventions. However, the fixed position of the scanning plane in combination with high exposure factors may lead to high cumulative patient skin doses that can reach deterministic threshold limits. The staff is also exposed to a considerable amount of scatter radiation while standing next to the patient during the procedures. Although some studies have been published dealing with this subject, data of patient skin doses determined by direct in vivo dosimetry remains scarce. The purpose of this study is to quantify and to evaluate both patient and staff doses by direct thermoluminescent dosimetry during various clinical CT fluoroscopy guided procedures. Patient doses were quantified by determining the entrance skin dose with direct thermoluminescent dosimetry and by estimating the effective dose (E). Staff doses were quantified by determining the entrance skin dose at the level of the eyes, thyroid, and both the hands with direct thermoluminescent dosimetry. For a group of 82 consecutive patients, the following median values were determined (data per procedure): patient E (19.7 mSv), patient entrance skin dose (374 mSv), staff entrance skin dose at eye level (0.21 mSv), thyroid (0.24 mSv), at the left hand (0.18 mSv), and at the right hand (0.76 mSv). The maximum recorded patient entrance skin dose stayed well below the deterministic threshold level of 2 Gy. Poor correlation between both patient/staff doses and integrated procedure mAs emphasizes the need for in vivo measurements. CT fluoroscopy doses are markedly higher than classic CT-scan doses and are comparable to doses from other interventional radiological procedures. They consequently require adequate radiation protection management. An important potential for dose reduction exists by limiting the fluoroscopic screening time and by reducing the tube current (mA) to a level sufficient to provide adequate image quality.

Adolescent↗

PubMed2005

Dynamic buckling and fragmentation in brittle rods.

We present experiments on the dynamic buckling and fragmentation of slender rods axially impacted by a projectile. By combining the results of Saint-Venant and elastic beam theory, we derive a preferred wavelength lambda for the buckling instability, and experimentally verify the resulting scaling law for a range of materials including teflon, dry pasta, glass, and steel. For brittle materials, buckling leads to the fragmentation of the rod. Measured fragment length distributions show two peaks near lambda/2 and lambda/4. The nonmonotonic nature of the distributions reflect the influence of the deterministic buckling process on the more random fragmentation processes.

Journal Article↗

PubMed2000

Contemporary research on parenting. The case for nature and nurture.

Current findings on parental influences provide more sophisticated and less deterministic explanations than did earlier theory and research on parenting. Contemporary research approaches include (a) behavior-genetic designs, augmented with direct measures of potential environmental influences; (b) studies distinguishing among children with different genetically influenced predispositions in terms of their responses to different environmental conditions; (c) experimental and quasi-experimental studies of change in children's behavior as a result of their exposure to parents' behavior, after controlling for children's initial characteristics; and (d) research on interactions between parenting and nonfamilial environmental influences and contexts, illustrating contemporary concern with influences beyond the parent-child dyad. These approaches indicate that parental influences on child development are neither as unambiguous as earlier researchers suggested nor as insubstantial as current critics claim.

Animals↗

PubMed2005

Children's residential exposure to chlorpyrifos: application of CPPAES field measurements of chlorpyrifos and TCPy within MENTOR/SHEDS-Pesticides model.

The comprehensive individual field-measurements on non-dietary exposure collected in the Children's-Post-Pesticide-Application-Exposure-Study (CPPAES) were used within MENTOR/SHEDS-Pesticides, a physically based stochastic human exposure and dose model. In this application, however, the model was run deterministically. The MENTOR/SHEDS-Pesticides employed the CPPAES as input variables to simulate the exposure and the dose profiles for seven children over a 2-week post-application period following a routine residential and professional indoor crack-and-crevice chlorpyrifos application. The input variables were obtained from a personal activity diary, microenvironmental measurements and personal biomonitoring data obtained from CPPAES samples collected from the individual children and in their homes. Simulation results were compared with CPPAES field measured values obtained from the children's homes to assess the utility of the different microenvironmental data collected in CPPAES, i.e. indicator toys and wipe samplers to estimate aggregate exposures that can be result from one or more exposure pathways and routes. The final analyses of the database involved comparisons of the actual data obtained from the individual biomarker samples of a urinary metabolite of chlorpyrifos (TCPy) and the values predicted by MENTOR/SHEDS-Pesticides using the CPPAES-derived variables. Because duplicate diet samples were not part of the CPPAES study design, SHEDs-Pesticides simulated dose profiles did not account for the dietary route. The research provided more confidence in the types of data that can be used in the inhalation and dermal contact modules of MENTOR/SHEDS-Pesticides to predict the pesticide dose received by a child. It was determined that we still need additional understanding about: (1) the types of activities and durations of activities that result in non-dietary ingestion of pesticides and (2) the influence of dietary exposures on the levels of TCPy found in the urine.

Air Pollutants↗

PubMed1991

Approximate entropy as a measure of system complexity.

Techniques to determine changing system complexity from data are evaluated. Convergence of a frequently used correlation dimension algorithm to a finite value does not necessarily imply an underlying deterministic model or chaos. Analysis of a recently developed family of formulas and statistics, approximate entropy (ApEn), suggests that ApEn can classify complex systems, given at least 1000 data values in diverse settings that include both deterministic chaotic and stochastic processes. The capability to discern changing complexity from such a relatively small amount of data holds promise for applications of ApEn in a variety of contexts.

Journal Article↗

PubMedDate not supplied

Non-deterministic individual responses to receptor-selective opioid agonists.

To assess within a single rat strain individual variability of analgesic responses to sub-ED50 doses of receptor-selective opioids, we measured: 1) tail flick latency (TFL) responses after intrathecal (ith) injection of delta, mu, and kappa agonists administered serially; 2) TFL and tail pinch latencies (TPch) after intravenous (iv) mu and kappa agonists; and 3) TFL and TPch after iv agonists of mu or combined mu + delta selectivity. Mean values in each study confirmed an analgesic response, but individual TFL and TPch responses were chaotic and, within each study, rank order correlations between TFL and TPch values within or between drugs were insignificant. Our results suggest a hypothesis that such responses are intrinsically nondeterministic because--resembling other complex dynamic systems--they are generated by stochastic receptor-transmitter interactions that in turn evoke a series of nonlinearly coupled cellular and neural events.

Amino Acid Sequence↗

PubMed1999

Role of the medical physicist in interventional radiology.

Interventional radiological procedures have significantly increased the probability for the expression of deterministic detriment to the patient. It is the responsibility of the consulting medical physicist to undertake the responsibility that (i) appropriate equipment is specified and purchased; (ii) the equipment purchased produces the best possible image quality for the minimum dose; (iii) accurate dosimetry is measured, calculated and recorded; (iv) interventional physicians and surgeons are adequately trained in the fundamental techniques that will minimize the dose to both patients and staff, while maintaining high image quality; and (v) interventional protocols, record keeping and patient follow-up, in the case of deterministic doses, are appropriately implemented.

Health Physics↗

PubMed2003

Synchronous loss of quasispecies memory in parallel viral lineages: a deterministic feature of viral quasispecies.

Viral quasispecies are endowed with a memory of their past evolutionary history in the form of minority genomes of their mutant spectra. To determine the fate of memory genomes in evolving viral quasispecies, we have measured memory levels of antigenic variant of foot-and-mouth disease virus (FMDV) RED, which includes an Arg-Glu-Asp (RED) at a surface antigenic loop of the viral capsid. The RED reverted to the standard Arg-Gly-Asp (RGD), and the RED remained as memory in the evolving quasispecies. In four parallel evolutionary lineages, memory reduction followed a strikingly similar pattern, and at passage 60 memory levels were indistinguishable from those of control populations (devoid of memory). Nucleotide sequence analyses indicated that memory loss occurred synchronously despite its ultimate molecular basis being the stochastic occurrence of mutations in the evolving quasispecies. These results on the kinetics of memory levels have unveiled a deterministic feature of viral quasispecies. Molecular mechanisms that may underlie synchronous memory loss are the averaging of noise signals derived from mutational input, and constraints to genome diversification imposed by a nucleotide sequence context in the viral genome. Possible implications of the behaviour of complex, adaptive viral systems as experimental models to address primary mechanisms of neurological memory are discussed.

Amino Acid Sequence↗

PubMedDate not supplied

Evaluating the quality of anonymous record linkage using deterministic procedures with the New York State AIDS registry and a hospital discharge file.

Linkage of same-person records across multiple databases relies on high-quality, uniformly available identifying information. These data quality issues become increasingly important when personal names are not available for record linkage. Using deterministic decision criteria, we linked records from two population-based files in the absence of personal names. The sensitivity of anonymous record linkage procedures ranged from 32 to 85 per cent for the two years studied, and the positive predictive value (PPV) ranged from 14 to 99 per cent. Decreasing sensitivity and PPV were primarily attributed to (1) errors in computerized identifying information and (2) the deterministic decision criteria specified for record linkage. An evaluation of the contribution of personal names to the quality of record linkage found no measurable impact.

Acquired Immunodeficiency Syndrome↗

PubMedDate not supplied

Economic value of caregiver effort in maintaining long-term ventilator-assisted individuals at home.

OBJECTIVE: To estimate the economic value of caregivers' efforts in maintaining ventilator-assisted individuals at home. DESIGN: Nonexperimental, cross-sectional survey. SETTING: Households of home-based ventilator-assisted individuals residing in 37 states. PARTICIPANTS: Caregivers of 1404 ventilator-assisted individuals; 277 (19.7%) responses were received. OUTCOME MEASURES: The Home Ventilator Care Cost and Utilization Survey and the Modified Katz Index. METHODS: The economic value of caregiver effort was estimated deterministically by opportunity cost, aggregated market value, and aggregated replacement cost and estimated stochastically by ordinary least squares regression. Cost of formal home care services was estimated with the Medicare Schedule of Limits for Home Health Agency Costs. Estimates of total cost of home care for each method of valuing caregiver effort were calculated by summing the cost of formal home care services with the value of caregiver effort. RESULTS: The average monthly cost of formal home care services was estimated to be $6411 (SD, $8490; median, $2006; range, $0 to $38,607). After adding various values of caregiver effort to the cost of formal home care services, the average cost of home care increases by $960 to $12,483, depending on the method used to calculate the value of the caregiver's time; the median total cost of home care increased by $1403 to $17,793. Data also showed that, depending on the figure used to estimate the cost of long-term care and which method was used to calculate caregiver value, home care was more expensive for at least 4.6% of ventilator-assisted individuals and for as many as 36.7%. CONCLUSIONS: The incorporation of the caregiver's time value into cost estimates did not substantially reduce the proportion of patients for whom home care was the least expensive alternative, except when caregiver effort was valued at a registered nurse's wage rate. However, the methods used to place an economic value on caregiver effort did not take into consideration the long-term economic impact on caregivers who reduce their work hours or forego employment or educational opportunities, nor did they take into account the lost wages of the ventilator-assisted individual or the extent to which the caregiver was financially dependent on the ventilator-assisted individual.

Adult↗

PubMed2001

Harmonization of future needs for dermal exposure assessment and modeling: a workshop report.

Dermal exposure assessment and modeling is still in early phases of development. This article presents the results of a workshop organized to harmonize the future needs in this field. Methods for dermal exposure assessment either assess the mass of contaminant that is transferred to the skin, or the transfer of contaminant through the skin. Models for dermal exposure are either knowledge-based or deterministic. Any method or model should be transparent, validated, and open to further development. Some (partly) validated and standardized methods are available for measuring or modeling permeation of the skin or of personal protective equipment (PPE). Further validation and standardization is necessary. More research is needed on permeation of dusts and aerosols and more realistic tests should be developed and used for PPE. Several methods have been developed to measure contamination of surfaces or skin, but they are not validated or standardized. A number of non-validated models exist to assess dermal exposure. A clear need exists for more studies of dermal exposure, regarding measurement methods, models and actual exposure levels. A running four-year European study will greatly expand the knowledge in this field. Simple tools to assess and control the risks of dermal exposure in small and medium sized enterprises are also needed. Increasing the general knowledge of practitioners (e.g., safety professionals, occupational hygienists and physicians) in the field of dermal exposure is a first requirement. Available data, for example, on the permeation of PPE, should be made more readily available, using modern information technology. When information on dermal exposure is gathered and stored, the core information needs are partly the same as those for inhalation exposure. Some elements of process and activity, substance and product or worker, specific for dermal exposure, have been suggested by the workshop.

Europe↗

PubMed2006

Universal quantum computation in decoherence-free subspace with neutral atoms.

We show how realistic cavity-assisted interaction between neutral atoms and coherent optical pulses, and measurement techniques, combined with optical transportation of atoms, allow for a universal set of quantum gates acting on decoherence--free subspace in a deterministic way. The logical qubits are immunized to the dominant source of decoherece-dephasing, while the influences of additional errors are shown by numerical simulations. We analyze the performance and stability of all required operations and emphasize that all techniques are feasible with current experimental technology.

Journal Article↗

PubMedDate not supplied

[Road and home-accident injuries of infants and adolescents in the Lazio region. Results of an integrated surveillance system].

OBJECTIVE: road traffic and home accidents are one of the leading causes of death for infants and adolescents between 0-18 years of age. This study aimed to describe the injuries of children in the Lazio Region, in the year 2000. DESIGN: retrospective cohort study. SETTING: road traffic and home accident injury visits to all Emergency Departments (ED) in the Lazio region during 2000, Hospital discharges in the region during 2000-2001, integrated through deterministic linkage strategy PARTICIPANTS: all children aged 0-18 who visited one of the ED for home or road traffic injuries. MAIN OUTCOME MEASURES: we computed ED visits and hospitalisation rates and stratified them by sex, age and place of residence. Cases were classified by body region and type of lesion. IRR and 95% confidence intervals have been estimated using Poisson Regression. RESULTS: the rate of home accident visits was particularly high among children aged 1-5 years (55.2/1000), while the highest rate for road traffic injuries was in 14-18 year old children (53.8/1000). Girls had a lower hospitalisation rate than boys. Higher hospitalisation rates were found for children living outside of Rome. The body region most frequently injured in road traffic accidents was the lower extremities (28.4%), while most frequently injured in home accidents was the head and neck (34.8%). CONCLUSION: this study shows how integrating different systems of surveillance can provide a more complete picture of injuries from road and home accidents, that is difficult to obtain using other sources. The youngest children are at high risk of home accidents while teen-agers are at risk for road traffic injuries.

Accidents, Home↗

PubMedDate not supplied

Matching solute breakthrough with deterministic and stochastic aquifer models.

Two different deterministic and two alternative stochastic (i.e., geostatistical) approaches to modeling the distribution of hydraulic conductivity (K) in a nonuniform (sigma2ln(K)) = 0.29) glacial sand aquifer were used to explore the influence of conceptual model selection on simulations of three-dimensional tracer movement. The deterministic K models employed included a homogeneous effective K and a perfectly stratified 14 layer model. Stochastic K models were constructed using sequential Gaussian simulation and sequential i ndicator simulation conditioned to available K values estimated from measured grain size distributions. Standard simulation software packages MODFLOW, MT3DMS, and MODPATH were used to model three-dimensional ground water flow and transport in a field tracer test, where a pulse of bromide was injected through an array of three fully screened wells and extracted through a single fully screened well approximately 8 m away. Agreement between observed and simulated transport behavior was assessed through direct comparison of breakthrough curves (BTCs) and selected breakthrough metrics at the extraction well and at 26 individual multilevel sample ports distributed irregularly between the injection and extraction wells. Results indicate that conceptual models incorporating formation variability are better able to capture observed breakthrough behavior. Root mean square (RMS) error of the deterministic models bracketed the ensemble mean RMS error of stochastic models for simulated concentration vs. time series, but not for individual BTC characteristic metrics. The spatial variability models evaluated here may be better suited to simulating breakthrough behavior measured in wells screened over large intervals than at arbitrarily distributed observation points within a nonuniform aquifer domain.

Bromides↗