SEARCH · PubMed Health

Results for “Deterministic Measurement”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources

PubMed1991

Selection within and across populations in livestock improvement.

Genetic evaluations within and across populations (countries, breeds, herds) allow ranking on estimated genetic merit and selecting breeding individuals across populations. Selection within and across populations (combined selection) should by definition always be as good as, or better than, within-population selection, the limiting case. The advantage depends on the sizes of the populations, the number of populations, the initial genetic means, and the correspondence of the breeding objectives in the different populations, as measured by the genetic correlation for economic merit. The advantages of combined selection are evaluated deterministically for a simple case of selecting the best males for use across populations by using a common truncation line over the distributions of EBV for the different populations. Combined selection increases overall response rates in the cooperating populations. Where the initial genetic means are the same, small populations (100 males tested) benefit greatly from combined selection. Large populations (500 to 1,000 males tested) also benefit, but less. The results depend on the increased selection response to scale, response being approximately linear with the logarithm of the number tested. When the initial means differ, the genetically poorer population can catch up in three to five generations and then contribute to the increased responses with combined selection. When breeding objectives differ, selection usually gradually pulls the populations apart and they make less and less contribution to each other and finally become separate. These results have implications for breeding strategies. Their application would affect structures of populations and rates of genetic change possible by selection.

Animals↗

PubMed2001

The impact of alternative practices on the cost and quality of mammographic screening in the United States.

The decentralized structure of health care in the Unites States hinders population-based analysis of breast cancer screening. Our objectives are to model mammography in the United States as a whole, to identify the variables that most profoundly affect cost and efficacy, and to develop a strategy to improve mammography screening from a population perspective. A spreadsheet model was used to represent the variables of mammography screening in the United States. The population-based national screening program in Sweden provides a framework for comparison. The outcome measures are the aggregate cost and the number of cancers detected by mammography. We used deterministic sensitivity analysis to calculate the impact of variation in practice. Aggregate costs of screening in the United States are in the range of $3-$5 billion dollars. The percentage of women screened, cost per mammogram, cancer to biopsy ratio, recall rate, and cost of recall have the most profound effect on the quality and cost of a national screening program. Variance of these high-impact variables, based on the U.S. population, modifies the aggregate cost of screening by over $2 billion. As mammography screening in the United States increases to include all women over age 40, high-impact variables should be optimized to decrease costs and improve breast cancer detection. Our model establishes which parameters are most important.

Adult↗

PubMed1989

Comparison of the effects of enteral feeding with continuous and intermittent parenteral nutrition on hepatic triglyceride secretion in human beings.

Plasma triglyceride turnover was measured during steady-state conditions in 22 postoperative patients. Nine had received nutritional support with an enteral regimen, seven had received an equivalent regimen as continuous parenteral nutrition, and six received the same parenteral regimen as a cyclical infusion. After 5 days of nutritional support, each patient received an intravenous bolus of tritiated glycerol. Plasma radiolabeled triglyceride content was measured during the subsequent 24 hours. The data were analyzed by means of a simple deterministic model of plasma triglyceride kinetics and compared with the results obtained by stochastic analysis. The rates of hepatic triglyceride secretion obtained by deterministic analysis were higher than those obtained by the stochastic approach. However, the mode of delivery of the nutritional regimen did not affect the rate of hepatic triglyceride secretion regardless of the method of analysis. The results suggest that neither complete nutritional bypass of the gastrointestinal tract nor interruption of parenteral nutrition in an attempt to mimic normal eating has any effect on hepatic triglyceride secretion. Any beneficial effect that enteral feeding or cyclical parenteral nutrition may have on liver dysfunction associated with standard parenteral nutrition appears to be unrelated to changes in hepatic triglyceride secretion.

Aged↗

PubMed1996

[Evaluation of the degree of diabetic dysautonomy with the analysis of heart rate measured at rest with the FINAPRES system].

In this work, we developped the ERK (Eckmann, Ruelle and Khamporst) method of recurrent plots to analyse Heart Rate Variability (HRV), measured by the FINAPRES system in diabetic subjects. Our aim was to search some indices that might characterize the degree of dysautonomy detected in diabetic subjects, using the Ewing tests. The idea was to analyze the recurrences of the HR to previously observed values. When a value of HR, xi measured at the j-th beat come back to an already observed value, we compare the distances between the following measures (xi + 1 to xj + 1), (xj + 2 to xj + 2)... If the distances are under a given criteria during k beats, xi is deterministic of order k. Let n1 be the number of recurrent points and nk the number of k-order deterministic points, with k = 2, 3, 4... We defined the index of determinism nk + 1/nk and the Shannon entropy of the Nk = nk-nk + 1. These indices will be correlated to the total score of the 5 Ewing tests, which represent the standard measure to evaluate the diabetic dysautonomy. Blood pressure (BP) and HR were measured during about 30 minutes using the FINAPRES system in 44 healthy subjects and 60 non-hypertensive diabetic subjects. In the diabetic subjects, the age, the body weight and systolic and diastolic BP were 56 +/- 13 years (mean +/- standard-deviation), 79 +/- 14 kg, 80 +/- 10 mmHg and 137 +/- 20 mmHg. HR was weakly correlated to age (r = 0.29; p = 0.02) and the Ewing score (r = 0.31; p = 0.01). Its standard-deviation is also weakly correlated to age (r = 0.32; p = 0.01) and to the Ewing score (r = 0.34; p = 0.01). Using the ERK method, we obtained indices which are much more correlated to the Ewing score. In particular, the ratio n2/n1 and Shannon entropy were correlated to the Ewing score with r = 0.51 and r = 0.53, respectively (p < 0.0001 in both cases). These indices are also correlated to age (r = 0.40; p = 0.003) in both cases. The ERK method give some indices which are easy to obtain (measurement of HR during a rest period) and easy to interpret. These indices are strongly linked to the dysautonomy score which required a good cooperation of the patient and a great vigilance during its execution. This method could be applied to BP to explore BP regulation in hypertensive subjects.

Adult↗

PubMed1986

Effects of noise on some dynamical models in ecology.

We investigate effects of random perturbations on the dynamics of one-dimensional maps (single species difference equations) and of finite dimensional flows (differential equations for n species). In particular, we study the effects of noise on the invariant measure, on the "correlation" dimension of the attractor, and on the possibility of detecting the nonlinear deterministic component by applying reconstruction techniques to the time series of population abundances. We conclude that adding noise to maps with a stable fixed-point obscures the underlying determinism. This turns out not to be the case for systems exhibiting complex periodic or chaotic motion, whose essential properties are more robust. In some cases, adding noise reveals deterministic structure which otherwise could not be observed. Simulations suggest that similar results hold for flows whose attractor is almost two-dimensional.

Animals↗

PubMed1995

Statistical basis for the determination of optical pathlength in tissue.

In this paper we show how to derive the mean and variance of the transilluminated signal obtained in models of light propagation in tissue, based both on a stochastic Monte Carlo method and on a deterministic diffusion approximation. The theoretical treatment of the Monte Carlo model applies only to integrated intensity measurements, whereas the diffusion approximation gives an estimator for the time-dependent case as well. We present results that show the accurate prediction of Monte Carlo statistics, and propose that the diffusion approximation is therefore a suitable mechanism for incorporating noise into modelling procedures.

Animals↗

PubMed2002

Coda wave interferometry and the equilibration of energy in elastic media.

Multiple-scattered waves usually are not useful for creating deterministic images of the interior of elastic media. However, in many applications, one is not so much interested in making a deterministic image as in detecting changes in the medium. Cases in point are volcano monitoring and measuring the change in hydrocarbon reservoirs during enhanced recovery operations. Coda wave interferometry is a technique wherein changes in multiple-scattered waves are used as a diagnostic for minute changes in the medium. This technique was developed previously for scalar waves; however, the application of this technique in geophysics, nondestructive testing, and other applications where elastic waves are used, requires the extension of the existing formulation of coda wave interferometry to include conversions between P and S waves. Here, a simple model for the equilibration between P and S waves incorporates into the theory of coda wave interferometry the mode conversions that are inherent to multiply scattered elastic waves.

Journal Article↗

PubMedDate not supplied

An approach to the assessment of overall uncertainty of determination of dose using an ESR technique.

An approach to the assessment of overall uncertainty of dose reconstruction by means of an ESR with additive dose technique is proposed. This approach takes account of uncertainties caused by different sources giving a quantitative measure of uncertainty of the determined dose. Dose is determined as an interval assessment rather than a deterministic value, allowing for the analytical estimation of both the mean value and the 95% confidence intervals. The effects of the number of additional irradiations and the value of dose increment on the uncertainty of dose determination are analyzed.

Dental Enamel↗

PubMed1983

Expected relative responses to selection for alternative measures of life cycle economic efficiency of pork production.

Relative genetic responses to selection for alternative measures of economic efficiency of pork production were examined. The analysis was based on results from a deterministic bio-economic model of lifecycle pork production. Alternative aggregate breeding values considered were based on cost (+)/unit of live weight or of carcass output lean for different production systems and for different breeding roles of the selected stocks. For cost/unit of lean, changes in leanness (or fatness) dominated the index. For cost/unit of live weight, however, no one trait dominated the index, and changes in growth and reproductive traits as well as the breeding role of the stock (purebred, maternal or paternal) were important in defining selection objectives. Management and production systems were less important than breeding role for cost/unit live weight output, except that importance of growth rate was increased by marketing at the mean weight reached at a fixed age rather than at a fixed weight irrespective of age. Implications of these results for goals and systems of pig improvement are discussed.

Adipose Tissue↗

PubMed1989

The effect of the heartbeat on vocal fundamental frequency perturbation.

Signal-averaging and autocorrelation analysis revealed that the cardiovascular system exerts a modest but consistent influence on vocal fundamental frequency (Fo), accounting for approximately 0.5% to 20% of the absolute Fo perturbation (jitter) measured during a sustained phonation. There was also a marked trend for this percentage to decrease with increasing vocal Fo. Estimated mean "deterministic jitter" (Jd) values of 3.7 microsec (SD = 3.2) and 0.9 microsec (SD = 0.5) were derived from 6 normal male and 6 normal female subjects, respectively, with an overall mean of 2.3 microsec (SD = 2.7). These values represent approximately 6.9% of the mean total jitter for men and 2.4% of the mean total jitter for women, or about 4.6% for all subjects. The results are discussed in terms of their significance regarding more reliable vocal jitter measurement.

Adult↗

PubMed2000

Interrelations among distortion-product phase-gradient delays: their connection to scaling symmetry and its breaking.

Distortion-product-otoacoustic-emission (DPOAE) phase-versus-frequency functions and corresponding phase-gradient delays have received considerable attention because of their potential for providing information about mechanisms of emission generation, cochlear wave latencies, and characteristics of cochlear tuning. The three measurement paradigms in common use (fixed-f1, fixed-f2, and fixed-f2/f1) yield significantly different delays, suggesting that they depend on qualitatively different aspects of cochlear mechanics. In this paper, theory and experiment are combined to demonstrate that simple phenomenological arguments, which make no detailed mechanistic assumptions concerning the underlying cochlear mechanics, predict relationships among the delays that are in good quantitative agreement with experimental data obtained in guinea pigs. To understand deviations between the simple theory and experiment, a general equation is found that relates the three delays for any deterministic model of DPOAE generation. Both model-independent and exact, the general relation provides a powerful consistency check on the measurements and a useful tool for organizing and understanding the structure in DPOAE phase data (e.g., for interpreting the relative magnitudes and intensity-dependencies of the three delays). Analysis of the general relation demonstrates that the success of the simple, phenomenological approach can be understood as a consequence of the mechanisms of emission generation and the approximate local scaling symmetry of cochlear mechanics. The general relation is used to quantify deviations from scaling manifest in the measured phase-gradient delays; the results indicate that deviations from scaling are typically small and that both linear and nonlinear mechanisms contribute significantly to these deviations. Intensity-dependent mechanisms contributing to deviations from scaling include cochlear-reflection and wave-interference effects associated with the mixing of distortion- and reflection-source emissions (as in DPOAE fine structure). Finally, the ratio of the fixed-f1 and fixed-f2 phase-gradient delays is shown to follow from the choice of experimental paradigm and, in the scaling limit, contains no information about cochlear physiology whatsoever. These results cast considerable doubt on the theoretical basis of recent attempts to use relative DPOAE phase-gradient delays to estimate the bandwidths of peripheral auditory filters.

Animals↗

PubMed2001

[Multidimensional, nonlinear pain concept. A broad approach for explaining and understanding complex pain syndromes].

The traditional mechanistic, deterministic, point-to-point-model of Descartes with its modifications of specificity, intensity, pattern and gate-control-theory turned out to be suitable for acute pain. Symptomatic pain as a result of a lesion or organic disease has to be differentiated principally from multifactorial pain syndromes. They can be regarded as open dynamic systems. The implication of consciousness of chronic pain patients with its essential intentionality opens degrees of freedom for the patients on the one hand, but uncertainty in the response to treatment measures, compliance and prognosis on the other hand. For complex regional pain, for chronifying syndromes and for the majority of chronic pain states the non-deterministic, non-linear, multidimensional pain concept is proposed.

Complex Regional Pain Syndromes↗

PubMed1990

Stochastic methods in population forecasting.

"This paper presents a stochastic version of the demographic cohort-component method of forecasting future population. In this model the sizes of future age-sex groups are non-linear functions of random future vital rates. An approximation to their joint distribution can be obtained using linear approximations or simulation. A stochastic formulation points to the need for new empirical work on both the autocorrelations and the cross-correlations of the vital rates. Problems of forecasting declining mortality and fluctuating fertility are contrasted. A volatility measure for fertility is presented. The model can be used to calculate approximate prediction intervals for births using data from deterministic cohort-component forecasts. The paper compares the use of expert opinion in mortality forecasting with simple extrapolation techniques to see how useful each approach has been in the past. Data from the United States suggest that expert opinion may have caused systematic bias in the forecasts."

Age Distribution↗

PubMed2001

Apamin-induced irregular firing in vitro and irregular single-spike firing observed in vivo in dopamine neurons is chaotic.

Dopamine neurons of the substantia nigra often fire action potentials irregularly in vivo, but in vitro fire in a regular, pacemaker-like firing pattern. Bath application of apamin, a blocker of calcium-activated potassium channels, can shift a dopamine neuron from pacemaker-like to irregular firing. To determine whether the irregular firing was caused by intrinsic cellular mechanisms rather than random synaptic input or some other form of noise, spike density functions of interspike interval records were analyzed using non-linear forecasting methods to quantify any non-linear (non-periodic) structure. Intrinsic cellular mechanisms are capable of producing chaotic firing, which is deterministic, non-linear, and loses predictability exponentially with increasing forecast time.To determine whether forecasting spike density functions could reliably measure predictability, forecasting was first applied to spike density functions produced by computer simulations of pacemaker-like, chaotic, and random firing, as well as pacemaker-like and chaotic firing that were randomly synaptically driven. Exponential loss of predictability was successfully detected in both chaotic and randomly driven chaotic firing. Predictability scaled faster than exponentially for random spiking, and linearly (slower than exponentially) for randomly driven pacemaker firing. The method was then applied to experimental records of apamin-induced irregular firing of rat dopaminergic neurons of the substantia nigra in vitro and in vivo. Exponential loss of predictability was detected in both cases, consistent with chaotic firing. Experimental records of pacemaker-like firing in vitro showed linear scaling, consistent with a randomly driven pacemaker. Several schemes for neural encoding of synaptic inputs have been suggested, such as rate codes or temporal codes. However, our results suggest that under some conditions, the irregular firing of dopamine neurons does not reflect the random temporal dynamics of its inputs, but rather the intrinsic, deterministic dynamics of dopamine cells themselves, under the tonic neuromodulatory influence of apamin in vitro and possibly that of an unidentified endogenous modulatory substance in vivo.

Action Potentials↗

PubMed2002

Nonlinear analysis of irregular animal vocalizations.

Animal vocalizations range from almost periodic vocal-fold vibration to completely atonal turbulent noise. Between these two extremes, a variety of nonlinear dynamics such as limit cycles, subharmonics, biphonation, and chaotic episodes have been recently observed. These observations imply possible functional roles of nonlinear dynamics in animal acoustic communication. Nonlinear dynamics may also provide insight into the degree to which detailed features of vocalizations are under close neural control, as opposed to more directly reflecting biomechanical properties of the vibrating vocal folds themselves. So far, nonlinear dynamical structures of animal voices have been mainly studied with spectrograms. In this study, the deterministic versus stochastic (DVS) prediction technique was used to quantify the amount of nonlinearity in three animal vocalizations: macaque screams, piglet screams, and dog barks. Results showed that in vocalizations with pronounced harmonic components (adult macaque screams, certain piglet screams, and dog barks), deterministic nonlinear prediction was clearly more powerful than stochastic linear prediction. The difference, termed low-dimensional nonlinearity measure (LNM), indicates the presence of a low-dimensional attractor. In highly irregular signals such as juvenile macaque screams, piglet screams, and some dog barks, the detectable amount of nonlinearity was comparatively small. Analyzing 120 samples of dog barks, it was further shown that the harmonic-to-noise ratio (HNR) was positively correlated with LNM. It is concluded that nonlinear analysis is primarily useful in animal vocalizations with strong harmonic components (including subharmonics and biphonation) or low-dimensional chaos.

Animals↗

PubMed1981

Clocked cell cycle clocks.

The cell division cycle of both mammalian cells and microorganisms, which apparently has both deterministic and probabilistic features, is a clock of sorts in that the sequence of events that comprise it measures time under a given set of environmental conditions. The cell division cycle may itself be regulated by a programmable clock that, under certain conditions, can generate circadian periodicities by interaction with a circadian pacemaker. These clocks must insert time segments into the cell division cycle in order to generate the observed variability in cellular generation times.

Animals↗

PubMed2001

Exploring the impact of prevalence and mortality on incidence of dementia in the oldest old: the sensitivity of a deterministic approach.

BACKGROUND: There has been considerable debate about whether dementia is an age-related or an aging-related phenomenon. When the evidence is restricted to prevalence data, the inferences are not sound because incidence, mortality and differential mortality are not taken into account. The aim of the paper is to demonstrate the use and sensitivity of a deterministic model based on the relationship between mortality, incidence and prevalence with the example of the chronic disease dementia. DESIGN: The simple deterministic model used here allows the calculation of one component given the other three. The sensitivity of calculated incidence to individual and combined changes in mortality, differential mortality (as measured by the mortality odds ratio) and prevalence is examined using published data. MAIN RESULTS: Calculated incidence continues to increase with age despite extreme but plausible changes in each of the other components. Calculated incidence declines amongst the oldest old only when the changes are combined. CONCLUSION: The deterministic model is shown to provide robust interrogation of the relationship between prevalence, incidence and survival. The effect incidence and survival have on the age-related and aging-related debate is illustrated. Only with extreme assumptions can the incidence of dementia be lessened. Clearly, more information on the oldest old is needed, but incidence studies of sufficient size at such great ages are problematic, and therefore there is a need to use flexible models for maximising the value of empirical data.

Aged↗

PubMed2003

Nonlinear dynamics indicates aging affects variability during gait.

OBJECTIVE: To investigate the nature of variability present in time series generated from gait parameters of two different age groups via a nonlinear analysis. DESIGN: Measures of nonlinear dynamics were used to compare kinematic parameters between elderly and young females. BACKGROUND: Aging may lead to changes in motor variability during walking, which may explain the large incidence of falls in the elderly. METHODS: Twenty females, 10 younger (20-37 yr) and 10 older (71-79 yr) walked on a treadmill for 30 consecutive gait cycles. Time series from selected kinematic parameters of the right lower extremity were analyzed using nonlinear dynamics. The largest Lyapunov exponent and the correlation dimension of all time series, and the largest Lyapunov exponent of the original time series surrogated were calculated. Standard deviations and coefficient of variations were also calculated for selected discrete points from each gait cycle. Independent t-tests were used for statistical comparisons. RESULTS: The Lyapunov exponents were found to be significantly different from their surrogate counterparts. This indicates that the fluctuations observed in the time series may reflect deterministic processes by the neuromuscular system. The elderly exhibited significantly larger Lyapunov exponents and correlation dimensions for all parameters evaluated indicating local instability. The linear measures indicated that the elderly demonstrated significantly higher variability. CONCLUSIONS: The nonlinear analysis revealed that fluctuations in the time series of certain gait parameters are not random but display a deterministic behavior. This behavior may degrade with physiologic aging resulting in local instability. RELEVANCE: Elderly show increased local instability or inability to compensate to the natural stride-to-stride variations present during locomotion. We hypothesized that this may be the one of the reasons for the increases in falling due to aging. Future efforts should attempt to evaluate this hypothesis by making comparisons to pathological subjects (i.e. elderly fallers), and examine the sensitivity and specificity of the nonlinear methods used in this study to aid clinical assessment.

Adult↗