PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “model predictive control”

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 739 records · Page 41Linked to original sources
PubMed1993

Microcomputer-assisted kinetic modeling of mammalian gene expression.

New software for microcomputers enables predictive, quantitative models of genetic systems to be produced that can account for the elements of time, scale, and feedback control of hierarchical systems. The flow of genetic information during protein synthesis can be addressed by treating each intermediate as a kinetic element in a linked series of reactions. When the rate of transcription changes, the time required to achieve a new level of the encoded protein is expected to be a function of the conversion rates or half-lives of all intermediates. Kinetic modeling may be used to make predictions and integrate primary data concerning rates of transcription, nuclear mRNA dynamics, nucleocytoplasmic transport, translational control, and other processes that govern the rate of synthesis for specific proteins.

Animals↗
PubMed1995

Empirical validation for a family-centered model of care.

OBJECTIVE: To examine whether family relations and family-life stress predict adherence behaviors and metabolic control in youths by testing a theoretically- and empirically-based model. RESEARCH DESIGN AND METHODS: HbA1c levels of 157 youths 12-20 years of age with insulin-dependent diabetes mellitus (IDDM) were evaluated, along with treatment adherence and psychosocial family data based on interviews and self-reports. A family-centered model for IDDM care was analyzed with the EQS structural modeling statistical program. An additional exploratory model including HbA1c levels 6 months earlier was also tested. RESULTS: Positive family relations (high family cohesion and low family conflict), especially during the first years of illness, indirectly related to good metabolic control through positive adherence behaviors. High levels of family-life stress related to worse metabolic control directly, and also indirectly via poor family relations, which in turn related to poor adherence to treatment. Longer illness duration related indirectly to metabolic control via adherence to treatment. Longer illness duration also related to maternal perceptions of higher family-life stress. Older youths perceived more family-life stress as well. The older age of the youths related indirectly to poor metabolic control through its association with poor adherence behaviors and less cohesive and more conflictual family relations. Results were consistent when earlier levels of metabolic control were included in the model, except that the direct relationship between family-life stress and metabolic control became nonsignificant. CONCLUSIONS: The findings suggest that a family-centered approach to diabetes care that facilitates positive family functioning and leads to lower levels of family-life stress may be useful in promoting optimal health outcomes.

Adolescent↗
PubMedDate not supplied

Effect of pregnancy on tissue distribution of salicylate in rats.

The effect of pregnancy on tissue distribution of salicylate was studied by comparing both pharmacokinetic and protein-binding parameters between 20-day-pregnant rats and nonpregnant (control) rats. In the pregnant rats, the volume of distribution increased significantly (p less than 0.05) from 164 ml/kg of the control to 225 ml/kg, and the total body clearance also increased significantly (p less than 0.05) from 12.1 ml/hr/kg of the control to 19.8 ml/hr/kg. But these changes did not affect the plasma disappearance half-life of salicylate in the pregnant rats. The serum unbound fraction (fs) of the pregnant rats at 8 hr after iv administration of salicylate increased remarkably from 0.14 of the control to 0.67. The fs in the fetal serum (0.41) was lower than that in the maternal serum in spite of the lower albumin concentration in the fetal serum. A nonlinear serum protein binding was observed both in the control and in the fetal rats, but not observed in the pregnant rats. In the pregnant rats, the tissue-to-serum concentration ratios (Kp) of all tissues studied were larger than those in the control rats, and the values of Kp in the fetal were larger than those in the maternal. To elucidate these difference in Kp values between the pregnant and control rats, a mathematical model was proposed, where salicylate was distributed in the interstitial fluid, bound to the interstitial albumin, and translocated into the intracellular fluid according to the pH partition theory. The Kp values of most tissues in the control and pregnant rats were predicted successfully by using this model.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2003

Caregiving and institutionalization of cognitively impaired older people: utilizing dynamic predictors of change.

PURPOSE: The purpose of this study was to identify reliable predictors of nursing home entry over a 3-year period in a sample of 3,944 persons with dementia who resided in a home setting at baseline. Strengths of the analysis include a multiregional recruitment strategy, incorporation of salient caregiver characteristics, and a 3-year prospective design that allows for the modeling of change in important variables (e.g., care recipient functional status or caregiving indicators) when time to institutionalization is predicted. DESIGN AND METHODS: Data were derived from the control sample of the Medicare Alzheimer's Disease Demonstration Evaluation (MADDE). A Cox proportional hazards model was used to predict time to institutionalization among individuals with dementia (baseline was enrollment into MADDE). Predictors included care recipient demographics, caregiver demographics, and time-varying measurements of care recipient functional status, caregiving indicators, and service utilization. Indicators of change were also incorporated to capitalize on the prospective data available. RESULTS: Although several results were consistent with prior findings, caregiving indicators (i.e., burden and self-rated health) and community-based service use were significant predictors of earlier placement. Change in caregiver instrumental activities of daily living and care recipient activities of daily living were also related to expedited institutionalization. IMPLICATIONS: The findings emphasize the importance of incorporating both care recipient and caregiver function and service use patterns when targeting programs designed to prevent or delay institutionalization for people with dementia.

Adult↗
PubMed2003

Modular organization of internal models of tools in the human cerebellum.

Human capabilities in manipulating many different tools with dexterity suggest modular neural organization at functional levels, but anatomical modularity underlying the capabilities has yet to be demonstrated. Although modularity in phylogenetically older parts of the cerebellum is well known, comparable modularity in the lateral cerebellum for cognitive functions remains unknown. We investigated these issues by functional MRI (fMRI) based on our previous findings of a cerebellar internal model of a tool. After subjects intensively learned to manipulate two novel tools (the rotated mouse whose cursor appeared at a rotated position, and the velocity mouse whose cursor velocity was proportional to the mouse position), they could easily switch between the two. The lateral and posterior cerebellar activities for the two different tools were spatially segregated, and their overlaps were <10%, even at low statistical thresholds. Activities of the rotated mouse were more anterior and lateral than the velocity mouse activities. These results were consistent with predictions by the MOdular Selection And Identification Controller (MOSAIC) model that multiple internal models compete to partition sensory-motor experiences and their outputs are linearly combined for a particular context.

Adult↗
PubMed2005

Functional imaging of changes in cerebellar activity related to learning during a novel eye-hand tracking task.

Coordination between the eyes and the hand is likely to be based on a process of motor learning, so that the interactions between the two systems can be accurately controlled. By using an unusual tracking task we measured the change in brain activation levels, as recorded with 3T functional magnetic resonance imaging (fMRI), between naïve human subjects and the same subjects after a period of extended training. Initially the performance of the two groups was similar. One subject group was then trained in a synchronous, coordinated, eye-hand task; the other group trained with a 304 ms temporal offset between hand and eye tracking movements. After training, different patterns of performance were observed for the groups, and different functional activation profiles. Significant change in the relationship between functional activation levels and eye-hand task conditions was predominantly restricted to visuo-motor areas of the lateral and vermal cerebellum. In an additional test with one of the subject groups, we show that there was increased cerebellar activation after learning, irrespective of change in performance error. These results suggest that two factors contribute to the measured blood oxygen level-dependent (BOLD) signal. One declined with training and may be directly related to performance error. The other increased after training, in the test conditions nearest to the training condition, and may therefore be related to acquisition of experience in the task. The loci of activity changes suggest that improved performance is because of selective modified processing of ocular and manual control signals within the cerebellum. These results support the suggestion that coordination between eye and hand movement is based on an internal model acquired by the cerebellum that provides predictive signals linking the control of the two effectors.

Adult↗
PubMed2002

Three-dimensional models of proteases involved in patterning of the Drosophila Embryo. Crucial role of predicted cation binding sites.

Three-dimensional models of the catalytic domains of Nudel (Ndl), Gastrulation Defective (Gd), Snake (Snk), and Easter (Ea), and their complexes with substrate suggest a possible organization of the enzyme cascade controlling the dorsoventral fate of the fruit fly embryo. The models predict that Gd activates Snk, which in turn activates Ea. Gd can be activated either autoproteolytically or by Ndl. The three-dimensional models of each enzyme-substrate complex in the cascade rationalize existing mutagenesis data and the associated phenotypes. The models also predict unanticipated features like a Ca(2+) binding site in Ea and a Na(+) binding site in Ndl and Gd. These binding sites are likely to play a crucial role in vivo as suggested by mutant enzymes introduced into embryos as mRNAs. The mutations in Gd that eliminate Na(+) binding cause an apparent increase in activity, whereas mutations in Ea that abrogate Ca(2+) binding result in complete loss of activity. A mutation in Ea predicted to introduce Na(+) binding results in apparently increased activity with ventralization of the embryo, an effect not observed with wild-type Ea mRNA.

Animals↗
PubMed1999

[Blood glucose self-monitoring (BGSM): an evaluation of its prescription and results in type-2 diabetes. The Research Group in Primary Care of Tortosa].

OBJECTIVES: To investigate the results of metabolic control among type-2 diabetics who practise self-monitoring of their blood glucose (MBG) and compare them with those who do not; the adequacy of MBG prescription according to clinical criteria and frequency of use; and to analyse the presence of factors predicting metabolic control. DESIGN: Descriptive and retrospective study covering 1995, 1996 and 1997. SETTING: The seven health districts in the territorial ambit of Tortosa Primary Care. PATIENTS: 597 type-2 diabetes patients were evaluated: 286 practising MBG, and 311 not doing so. All of them belonged to the health districts reference population. The sample was systematized and stratified by health districts in order to obtain data through a pre-designed data collection form. MEASUREMENTS AND MAIN RESULTS: 41.06% of diabetics practised MBG on a stable basis, without any significant differences showing in either HbA1c percentage, in any of the biological variables defining metabolic control in relation to the practice or otherwise of MBG, or in its frequency. An inverse relationship (p = 0.012) between the frequency of MBG and age was shown. Some clinical indication for prescribing MBG existed in 78.22% of the total diabetic population. In the diabetic population using MBG, inappropriate use of quantity was 54.89% (84.07% by too little, 15.92% in excess). Only 37.9% displayed quantitative and qualitative concordance simultaneously. The logistic model applied to the total diabetic population predicted 73.19% metabolic control with the variables of BMI (OR = 1.0542). Karnofsky index (OR = 0.9768) and presence of macroangiopathy (OR = 0.4249). CONCLUSIONS: 1. The practice of MBG is questionable, since the effectiveness found was not superior. 2. There is an imbalance between the real practice of MBG according to the clinical recommendations and consumption, which tends to be deficient. 3. The results do not seem to depend so much on MBG practice as on other linked circumstances which cannot be modified by MBG practice.

Aged↗
PubMedDate not supplied

[Motor learning with the minimal involvement of visual afferentation].

Amongst motor control and learning models, "A Cerebellar Model of Timing and Prediction" of A. Barto and J. Houk is the most interesting and physiologically well-grounded. Developing D. Marr's "The Theory of Cerebellar Cortex", this model proposed the important role in motor learning of the ability of Purkinje cells to change their activity level by the dendritic bistability mechanism. The aim of this investigation was to verify this idea in experiments with human learning of precise elbow flexion. The unsupervisual method of learning was used in order to guarantee the principal role of proprioception in training. The experiments were carried out in darkness to exclude the vision control. Subjects were asked to perform a precise horizontal elbow flexion as fast as possible and repeat this action from 30 to 50 times up to the point of complete movement acquisition (stable movement with the error in the range of 5% of a given flexion amplitude). The target point (a given angle of the horizontal elbow flexion) was not presented to the subjects in advance. Reaching the target point was indicated by a short light flash. During training, subjects learned to hit target point with the given precision. Kinematic characteristics of the movement (time change of elbow flexion angle, velocity, and acceleration) together with EMG of the flexor and extensor were recorded. The obtained results were in good agreement with J. Houk and A. Barto's hypothesis. Analysis of changes in the kinematic characteristics in the course of training revealed an asymmetric velocity profile and a fragmentary shape of acceleration profile at the beginning of learning. In the course of training, the acceleration profile transformed into biphasic curve with a single change in polarity. Thus, it acquired a characteristic shape of a plateau. Correspondingly, to the end of training, the character of the asymmetry of the velocity profile changed. No correlation was observed between the velocity parameters and movement precision. These features essentially distinguish the motor reactions under study from the common visuomotor coordinations. It is suggested that the amplitude and duration of the acceleration plateau reflect the intensity and time of inhibition of the descending activity of Purkinje cells as a result of bistability (in accordance with Houk and Barto's hypothesis).

Adolescent↗
PubMed1999

Modelling molecular mechanisms controlling sequential gene expression in differentiating mammalian enterocytes.

The gut epithelium represents a continuous developmental system in which cell proliferation in intestinal crypts is followed by the sequential expression of digestive and absorptive functions as enterocytes migrate out of crypts to the tips of intestinal villi. We have developed a mathematical model in the present work to mimic these sequential aspects of enterocyte differentiation. Using this model allows the characteristics of lactase expression to be ascribed to transcriptional control. In the case of a glucose transporter, however, it became necessary to assume an additional translational control that decreased exponentially as enterocytes migrated along villi. The suggestion that this type of modelling is useful in predicting which set of enterocytes is likely to use translation or transcription to control gene expression is also discussed.

Animals↗
PubMed2000

How honeybees make grazing landings on flat surfaces.

Freely flying bees were filmed as they landed on a flat, horizontal surface, to investigate the underlying visuomotor control strategies. The results reveal that (1) landing bees approach the surface at a relatively shallow descent angle; (2) they tend to hold the angular velocity of the image of the surface constant as they approach it; and (3) the instantaneous speed of descent is proportional to the instantaneous forward speed. These characteristics reflect a surprisingly simple and effective strategy for achieving a smooth landing, by which the forward and descent speeds are automatically reduced as the surface is approached and are both close to zero at touchdown. No explicit knowledge of flight speed or height above the ground is necessary. A model of the control scheme is developed and its predictions are verified. It is also shown that, during landing, the bee decelerates continuously and in such a way as to keep the projected time to touchdown constant as the surface is approached. The feasibility of this landing strategy is demonstrated by implementation in a robotic gantry equipped with vision.

Animals↗
PubMed1998

Two-Dimensional Automatic Control Modeling of a Posture Control System.

A posture control model has been developed on the basis of the 2-dimensional feedback control theory. Human postural characteristics were investigated in 5 healthy participants. Tests were performed with eyes open and eyes closed. After 5 s of quiet standing, each participant was unexpectedly pulled forward by 30 mm at his pelvis height and then released. Postural sway was measured over 20 s at a rate of 100 per second. Transfer functions to represent the posture control characteristic were identified by the least squares' method. These showed good results of the model's fitness, predictability, and stability. The response of the eyes-closed condition to perturbation is more oscillatory than that of the eyes-open condition. It seems that the model identified could be applicable to ergonomics, sports, or clinical situations.

model fitness↗
PubMed2005

Role of stretch-activated channels on the stretch-induced changes of rat atrial myocytes.

The role of stretch-activated channels (SACs) on the stretch-induced changes of rat atrial myocytes was studied using a computer model that incorporated various ion channels and transporters including SACs. A relationship between the extent of the stretch and the activation of SACs was formulated in the model based on experimental findings to reproduce changes in electrical activity and Ca(2+) transients by stretch. Action potentials (APs) were significantly changed by the activation of SACs in the model simulation. The duration of the APs decreased at the initial fast phase and increased at the late slow phase of repolarisation. The resting membrane potential was depolarised from -82 to -70 mV. The Ca(2+) transients were also affected. A prolonged activation of SACs in the model gradually increased the amplitude of the Ca(2+) transients. The removal of Ca((2+)) permeability through SACs, however, had little effect on the stretch-induced changes in electrical activity and Ca(2+) transients in the control condition. In contrast, the removal of the Na(+) permeability nearly abolished these stretch-induced changes. Plotting the peaks of the Ca((2+)) transients during the activation of the SACs along a time axis revealed that they follow the time course of the Na(i)(+) concentration. The Ca((2+)) transients were not changed when the Na(i)(+) concentration was fixed to a control value (5.4mM). These results predicted by the model suggest that the influx of Na(+) rather than Ca(2+) through SACs is more crucial to the generation of stretch-induced changes in the electrical activity and associated Ca(2+) transients of rat atrial myocytes.

Animals↗
PubMed1999

Genetic and nongenetic factors influencing plasma homocysteine levels in patients with ischemic cerebrovascular disease and in healthy control subjects.

Moderately elevated plasma homocysteine levels have been established as an independent risk factor for atherosclerosis and its complications, including cerebrovascular disease. A common mutation (C677T) in the gene encoding for the enzyme methylenetetrahydrofolate reductase (MTHFR) has been linked to increased plasma homocysteine levels in homozygous carriers, particularly in the presence of low folate levels. However, the results of most of the previous studies suggest that the C677T MTHFR mutation is not a significant risk factor for arterial disease. This discrepancy might, at least partly, be due to the fact that plasma homocysteine levels are influenced by several other factors, including age, gender, renal function, and vitamin status. We investigated the relation between plasma homocysteine levels, the C677T MTHFR mutation, and these other factors in a population of 96 patients with transient ischemic attacks or minor strokes and in 96 age- and sex-matched healthy control subjects. We further tested the value of a multivariate model for the prediction of plasma homocysteine levels under particular consideration of the MTHFR mutation status. In the patients, plasma homocysteine levels were significantly higher than in the healthy control subjects. With regard to the MTHFR mutation, the distribution of the C/C, C/T, and T/T genotypes was not significantly different between patients and healthy control subjects. Univariate (linear regression) analysis revealed significant (positive) correlations between plasma homocysteine levels on the one hand and age and creatinine on the other, the latter particularly in subjects with creatinine levels in the upper quartile. Significant (negative) correlations were found between plasma homocysteine levels, vitamin B12, and folate levels. However, these relations could much better be expressed by means of a multiplicative regression model. T/T subjects exhibited slightly higher homocysteine levels than C/C and C/T subjects; however, the differences between the 3 genotypes were not significant. Multivariate (stepwise regression) analysis revealed age, vitamin B12 levels, folate levels, and creatinine levels as significant independent variables influencing plasma homocysteine levels, whereas the MTHFR mutation status and gender were removed from the model. Considering all 192 subjects, only 28.8% of the variance of plasma homocysteine levels could be accounted for by the model. However, in homozygous carriers of the MTHFR mutation, the predictive power of the model is very high, explaining 76.1% of the variance of plasma homocysteine levels. According to our results, the C677T mutation does not constitute a major risk factor for transient ischemic attack or minor stroke, even under consideration of other possibly confounding factors that are known to affect plasma homocysteine levels. However, it is possible to predict plasma homocysteine levels in homozygous carriers of the mutation with high accuracy. The knowledge of the MTHFR mutation status may therefore help to identify subjects at high risk for hyperhomocysteinemia.

Adult↗
PubMed2005

Retrospective analyses and future predictions of snowmelt-induced acidification: example from a heavily impacted stream in the Czech Republic.

We have combined a long-term hydrochemistry model (MAGIC) with a model that predicts short-term transient changes in hydrochemistry (pBDM) during hydrological events in order to improve the temporal resolution of retrospective analyses and future predictions of streamwater acidification. The model has been applied to a heavily impacted catchment in the Czech Republic. Spring flood acid-neutralizing capacity (ANC), pH, and inorganic monomeric aluminum (Ali(n+)) were simulated for the years of 1860, 1900, 1930, 1950, 1965, and 1985, measured in 1999, and predicted for 2030 using two different emission control scenarios. If the emission reduction according to the current legislation scenario is implemented, the model predicts that the spring flood pH, ANC, and Ali(n+) will recover close to the level of the 1950s by 2030. This will occur despite the annual average chemistry being farfrom having recovered to that level. The results suggest that the recovery of spring flood events is faster then the recovery of annual average chemistry and that much of what is won by further emission reduction will not be fully realized on an annual time scale.

Acid Rain↗
PubMed1998

Elective induction versus spontaneous labor: a case-control analysis of safety and efficacy.

OBJECTIVE: To investigate the incidence, efficacy, and safety of elective induction in a community teaching hospital over 1 year. METHODS: This is a retrospective case-control study of rate, safety, and efficacy of all term inductions with vertex presentations judged to be elective by chart analysis. Cases were matched one for one for age, parity, and pay status with controls in spontaneous labor. The elective induction women were compared with those in spontaneous labor using chi2 Student t test, and Fisher exact test. Potential risk factors for cesarean delivery and neonatal intensive care unit (NICU) admission were then selected and subjected to bivariate analysis. Stepwise logistic regression was applied to control for confounding and to select which risk factors were important for those end points. RESULTS: There were 461 case-control pairs. The elective induction rate was 12.3%. Cesarean delivery was increased by elective induction in bivariate analysis (odds ratio [OR]=1.81, confidence interval [CI]=1.07, 3.08; power=.60). The cesarean delivery rate was 8.7% (control 5.0%). In a multiple regression model of potential risk factors for cesarean delivery, nulliparity (OR=6.14, CI=2.90, 13.04), cervical priming (OR=3.06, CI=1.46, 6.40), oxytocin usage (OR=2.82, CI=1.03, 7.75), gestational age at least 287 days (OR=2.51, CI=1.38, 4.58), and birth weight at least 3800 g (OR=2.29, CI=1.27, 4.13) were significant, but elective induction and epidural anesthesia were not. Elective induction did not significantly increase the rate of NICU admission (4.6% versus control 3.9%). In a multiple regression model of potential factors predicting NICU admission, only a 5-minute Apgar score of at most 8 was significant (OR = 12.34, CI=6.01, 25.3). CONCLUSION: Elective induction is commonly practiced, safe, and efficacious. Cesarean delivery is increased significantly by nulliparity and/or an unfavorable cervix, among other factors, but not by elective induction itself.

Adult↗
PubMed1989

Anthelmintic resistance and the control of ovine ostertagiasis: a drug action model for genetic selection.

A site-specific genetic prediction model is presented, which examines the influences of different anthelmintic treatment regimens on selecting for drug resistance within a sheep management system. The model exploits the power of modern microcomputers to integrate factors such as parasite strain, geographic location, management practice and genetic fitness to identify effective control regimens which do not lead to resistant Ostertagia circumcincta strains over a 30-year horizon. The potential use of the model as a farm level management-support tool is discussed.

Animals↗