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Results for “model predictive control”

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At least 919 records · Page 51Linked to original sources

PubMed1998

Selective versus non-selective antiarrhythmic approach for prevention of atrial fibrillation after coronary surgery: is there a need for pre-operative risk stratification? A prospective placebo-controlled study using low-dose sotalol.

AIM: This study evaluated the advantages of 'selective' over 'non-selective' antiarrhythmic prevention of atrial fibrillation after coronary surgery based on a new risk prediction algorithm. METHODS AND RESULTS: In a retrospective analysis of a prospective randomized trial, a model for risk prediction was determined based on clinical data of the control group (A; n = 107) and tested in a test group (B; n = 107, treated with low dose sotalol). Using this algorithm, the effect of a 'selective' antiarrhythmic approach in high-risk patients was compared to a 'non-selective' approach, where all patients were treated. In total, 75 (35%) patients developed atrial fibrillation and 14 (7%) side-effects led to discontinuation of study medication. Based on the risk prediction algorithm, 36% of group A patients were classified as high-risk patients with an incidence of atrial fibrillation of 76% compared to 26% in low-risk patients (P < 0.0001). The selective approach, i.e. treatment of high-risk patients only reduced the incidence of atrial fibrillation from 76% to 50% (P = 0.0295) compared to a reduction from 44% to 26% (P = 0.0065) when all patients were treated. More importantly, with the non-selective approach 100% of patients were exposed to the possible side-effects of sotalol and costs compared to 24% only with the selective approach (P < 0.0001). CONCLUSIONS: Thus, a selective approach based on a clinical risk prediction algorithm should improve the cost-effectiveness and safety of low-dose sotalol in the prevention of atrial fibrillation after coronary bypass surgery.

Adult↗

PubMed2002

Age- and size-related trends in woody plant shoot development: regulatory pathways and evidence for genetic control.

Woody plants exhibit significant and predictable patterns of change in morphology and physiology as they become older and larger. Four models of potential pathways controlling these changes are presented: a stimulus-response model in which fully developed organs respond to changes in environment (defined here as everything external to the organ); an extrinsic model in which the attributes of developing organs are determined by environmental factors; an intrinsic model in which changes are a result of programmed changes in gene expression; and an extrinsic-intrinsic model in which changes in gene expression are induced by environmental factors. We review evidence that a genetic component is involved in controlling age- and size-related changes in foliar morphology and physiology and discuss the possibility of complex interactions among model pathways.

Models, Biological↗

PubMed2003

Mathematical modelling of the cellular mechanics of plants.

The complex mechanical behaviour of plant tissues reflects the complexity of their structure and material properties. Modelling has been widely used in studies of how cell walls, single cells and tissue respond to loading, both externally applied loading and loads on the cell wall resulting from changes in the pressure within fluid-filled cells. This paper reviews what approaches have been taken to modelling and simulation of cell wall, cell and tissue mechanics, and to what extent models have been successful in predicting mechanical behaviour. Advances in understanding of cell wall ultrastructure and the control of cell growth present opportunities for modelling to clarify how growth-related mechanical properties arise from wall polymeric structure and biochemistry.

Biomechanical Phenomena↗

PubMed2006

A novel, model-based insulin and nutrition delivery controller for glycemic regulation in critically ill patients.

BACKGROUND: Critically ill patients are often hyperglycemic and insulin resistant, as well as highly dynamic. Tight glucose control has been shown to significantly reduce mortality in critical care. A physiological model of the glucose-insulin regulatory system is improved and used to develop an adaptive control protocol utilizing both nutritional and insulin inputs to control hyperglycemia. The approach is clinically verified in a critical care patient cohort. METHODS: A simple two-compartment model for glucose rate of appearance in plasma due to stepwise enteral glucose fluxes is developed and incorporated into a previously validated system model. A control protocol modulating intravenous insulin infusion and bolus, with an enteral feed rate, is developed, enabling tight and predictive glycemic regulation to preset targets. The control protocol is adaptive to patient time-variant effective insulin resistance. The model and protocol are verified in seven 10-h and one 24-h proof-of-concept clinical trials. Ethics approval was granted by the Canterbury Ethics Committee. RESULTS: Insulin requirements varied widely following acute changes in patient physiology. The algorithm developed successfully adapted to patient metabolic status and insulin sensitivity, achieving an average target acquisition error of 9.3% with 90.7% of all targets achieved within +/-20%. Prediction errors may not be distinguishable from sensor measurement errors. Large errors (>20%) are attributable to highly dynamic and unpredictable changes in patient condition. CONCLUSIONS: Tight, targeted stepwise regulation was exhibited in all trials. Overall, tight glycemic regulation is achieved in a broad critical care cohort with optimized insulin and nutrition delivery, effectively managing glycemia even with high effective insulin resistance.

Aged↗

PubMed2005

Performing hand actions assists the visual discrimination of similar hand postures.

Recent theoretical work has suggested that internal predictive signals are used for motor control and coordination. The predictive signal - proposed to be the output of a forward model - would be a sensory representation of action. Hence, these sensory representations could potentially influence other sensory processes. We report here how performance of hand actions assisted the visual discrimination of target hand postures presented at random times within an on-going series of hand images. Reaction times to discriminate the targets were significantly shorter when the displayed images were both sequential and congruent with the action being performed. Hence, the planning or execution of action appears to allow better prediction of a displayed series of congruent images. In further control experiments, we show that the motor-visual priming effect is unlikely to be due to differential attentional demands and it is specific to a first person perspective display; it is short lasting, being lost if a 500 ms delay is introduced between successive stimulus presentations. The data are interpreted as evidence supporting the hypothesis that forward models in the motor system provide action-specific sensory predictions that are available to cognitive processes.

Adolescent↗

PubMed2000

Parameters important in short antibiotic courses.

The aim of antibiotic therapy is pathogen eradication, which is often assumed on the basis of the alleviation of the signs and symptoms of the disease. Pharmacokinetic/pharmacodynamic in vitro and animal models have now been developed to predict bacteriological efficacy and to establish dosing regimens that are effective and control the development of resistance. These models may be applied to the evaluation of new short-course dosing regimens, lasting no longer than 3 - 5 days. Single-dose therapy, using agents with a prolonged duration of action, is currently employed for streptococcal pharyngitis, uncomplicated gonorrhoea and uncomplicated lower urinary tract infections in women. The use of short-course therapy in immunocompetent patients for the treatment of community-acquired infections that have a low bacterial load is feasible. Such regimens may have a number of advantages over those currently employed, which typically involve dosing for 7 - 10 days. These advantages include improved tolerability, reduction in healthcare costs, enhanced patient compliance and the prevention of the emergence of resistance.

Animals↗

PubMed1974

Tuberculosis in a rural population of South India: a five-year epidemiological study.

Tuberculosis is a serious health problem in India, but because of inadequate facilities for diagnosis in many parts of the country clinical data are incomplete. However, data on prevalence are available from a few sample surveys conducted in the general population during the last two decades. The study reported here provides information on the incidence of infection and disease as well as on the source and fate of cases. The information was obtained by means of surveys, repeated at intervals during 1961-68 in a randomly selected rural population of South India. In each survey, a tuberculin test was given and X-ray and sputum examinations were made. There were virtually no tuberculosis control facilities in the study area, since this was not covered by the national tuberculosis programme at the time.The annual rate of tuberculous infection in previously uninfected children and in adults was found to be about 1%. The incidence of tuberculosis (confirmed by culture) was about 1 per thousand (excluding children below the age of 5 years). About 30% of newly detected cases came from the population uninfected at an earlier survey. The prevalence of disease was four times as high as the incidence. Among cases found in the initial survey one-half died within 5 years and one-fifth continued to excrete bacilli after 5 years. Both infection and disease tended to decline during the observation period, though in an uneven manner that does not permit extrapolation. There was no evidence of an increase in drug-resistance among newly diagnosed cases. The findings of the study could be used in developing epidemetric models to predict the tuberculosis problem and to assess tuberculosis control measures applied in the community.

Adolescent↗

PubMed2006

Ready-to-eat breakfast cereal consumption enhances milk and calcium intake in the US population.

BACKGROUND: Inadequate intake of calcium-rich foods among US adults and children is a public health concern. Fluid milk is one of the best calcium sources because of its bioavailability and its versatility as both a beverage and a complement to various solid foods. One of the foods commonly consumed with milk is ready-to-eat breakfast cereal (RTEC). OBJECTIVE: We aimed to establish the association between the intake of RTEC, milk, and calcium within the context of the most current population dietary practices. We hypothesized that RTEC consumption facilitates milk consumption and is associated with adequacy of calcium intake in the US population. DESIGN: The most recent National Health and Nutrition Examination Survey, 1999-2000, data set was used as the source of data for this research. SUBJECTS/SETTING: US subjects aged 4 years and older (n=7,403), excluding pregnant and/or lactating women. Data were stratified according to sex and age (4 to 8 years, 9 to 13 years, 14 to 18 years, 19 to 30 years, 31 to 50 years, 51 to 70 years, and 71+ years), and then by consumption of breakfast, RTEC, and milk. STATISTICAL ANALYSES PERFORMED: SAS (release 8.1, 2000, SAS Institute Inc, Cary, NC) and SUDAAN (release 8.0.2, 2003, Research Triangle Institute, Research Triangle Park, NC) were used to calculate sample weighted means, standard errors, and population percentages. Multiple regression and multiple logistic regression models, with controls for covariates, were used to determine the predictability of total calcium intake from breakfast consumption compared to breakfast nonconsumption, and from inclusion of RTEC and milk in the breakfast meal compared with breakfast meal content without RTEC and milk. RESULTS: RTEC was predominantly consumed at breakfast. Average calcium intake at breakfast was seven times greater when RTEC was consumed with milk than when RTEC was consumed without milk. In multiple regression analyses, breakfast consumption, and milk consumption with or without RTEC all strongly predicted total daily calcium intake (P<0.05) while controlling for covariates. The percentage of respondents below the Adequate Intake level for calcium was higher for non-RTEC breakfast consumers than for RTEC breakfast consumers in all age-sex categories except those older than age 70 years, and girls aged 9 to 13 years. CONCLUSIONS: Consumption of RTEC at breakfast was associated with greater daily intake of both milk and calcium in all age and sex groups in the US population.

Adolescent↗

PubMed2002

External validation of a prognostic model for predicting survival of cirrhotic patients with refractory ascites.

OBJECTIVE: Cirrhotic patients with refractory ascites (RA) have a poor prognosis, although individual survival varies greatly. A model that could predict survival for patients with RA would be helpful in planning treatment. Moreover, in cases of potential liver transplantation, a model of these characteristics would provide the bases for establishing priorities of organ allocation and the selection of patients for a living donor graft. Recently, we developed a model to predict survival of patients with RA. The aim of this study was to establish its generalizability for predicting the survival of patients with RA. METHODS: The model was validated by assessing its performance in an external cohort of patients with RA included in a multicenter, randomized, controlled trial that compared large-volume paracentesis and peritoneovenous shunt. The values for actual and model-predicted survival of three risk groups of patients, established according to the model, were compared graphically and by means of the one-sample log-rank test. RESULTS: The model provided a very good fit to the survival data of the three risk groups in the validation cohort. We also found good agreement between the survival predicted from the model and the observed survival when patients treated with peritoneovenous shunt and with paracentesis were considered separately. CONCLUSION: Our survival model can be used to predict the survival of patients with RA and may be a useful tool in clinical decision making, especially in deciding priority for liver transplantation.

Actuarial Analysis↗

PubMed2001

A model-based approach to predicting BOD5 in settled sewage.

Rapid, accurate and reliable measurements of BOD are a very desirable basis for monitoring and controlling wastewater treatment works. Unfortunately, however, producing satisfactory measurements using hardware instrumentation has proved difficult. This paper addresses the issue of BOD estimation using a model-based approach. Two models are developed from historical data using neural network methods. The first model estimates the five-day BOD of the settled sewage using flow, solids, chloride and ammonia data and produces accurate predictions. The second model uses only flow and solids data as inputs yet still produces acceptable (although less accurate) predictions. It was concluded from this that satisfactory estimates of five day BOD can be produced using information that is relatively common to most works. The models are straightforward to apply on-line and offer a method of estimating five day BOD in real-time that is likely to be cheaper, more reliable and easier to maintain than hardware instrumentation.

Forecasting↗

PubMed1998

Begging as graded signals of need for food in young ring-billed gulls.

Recent models suggest that begging vocalizations are honest signals communicating a chick's nutritional needs to its parents. We investigated the effects on begging of short-term food deprivation ('hunger') and long-term reduction in body condition under controlled laboratory conditions in ring-billed gulls, Larus delawarensis. We tested two condition groups (high: fed to satiation; low: fed 75% wet mass of high-condition diet) at three levels of short-term food deprivation (1, 4 and 12 h). Begging call rate, intensity and peck rate were significantly greater in the low-condition chicks. Begging in both high- and low-condition groups increased with short-term deprivation, tending to asymptotic levels by 12 h of deprivation. Overall level of begging was graded according to both short- and long-term need for food, with steep slopes at the beginning of the begging curves providing a strong basis for parental discrimination of signalling level. The system appears to agree with the design requirements of a homeostatic control system, and with predictions of current game-theoretic models of honest signalling. Possible effects of sibling competition and parent-offspring conflict are discussed. These issues require further study under natural conditions in this species. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1992

A computational model of four regions of the cerebellum based on feedback-error learning.

We propose a computationally coherent model of cerebellar motor learning based on the feedback-error-learning scheme. We assume that climbing fiber responses represent motor-command errors generated by some of the premotor networks such as the feedback controllers at the spinal-, brain stem- and cerebral levels. Thus, in our model, climbing fiber responses are considered to convey motor errors in the motor-command coordinates rather than in the sensory coordinates. Based on the long-term depression in Purkinje cells each corticonuclear microcomplex in different regions of the cerebellum learns to execute predictive and coordinative control of different types of movements. Ultimately, it acquires an inverse model of a specific controlled object and complements crude control by the premotor networks. This general model is developed in detail as a specific neural circuit model for the lateral hemisphere. A new experiment is suggested to elucidate the coordinate frame in which climbing fiber responses are represented.

Animals↗

PubMed2002

Risk factors for the transmission of methicillin-resistant Staphylococcus aureus in an adult intensive care unit: fitting a model to the data.

Little is known about the amount of cross-transmission, the risk factors for infection, and the relative effectiveness of infection control procedures when methicillin-resistant Staphylococcus aureus (MRSA) infection occurs at highly endemic levels in intensive care units. A cohort study was done to identify exposures associated with cases that likely were the result of cross-transmission (i.e., occurring in clusters and with indistinguishable MRSA macrorestriction profiles). Fitting a simple stochastic model to the ascertained data allowed prediction of the effectiveness of infection control measures. Exposure to relative staff deficit (adjusted rate ratio, 1.05 independent; 95% confidence interval, 1.02-1.09) was the only factor significantly associated with potential transmission (P =.001). It was predicted that a 12% improvement in adherence to hand-hygiene policies might have compensated for staff shortage and prevented transmission during periods of overcrowding, shared care, and high workload but that this would be hard to achieve.

Cluster Analysis↗

PubMed1996

Transmission dynamics of Plasmodium falciparum.

Recent models of malaria have been developed by Gupta and her co-workers. A frequent assumption used to illustrate these models is that levels of malaria are controlled by lifelong strain-specific immunity. In this article, Allan Saul examines the predictions this model makes about the equilibrium values of parasite prevalence and the dynamics of an epidemic following the introduction of a new strain. He reaches the conclusion that the stability of malaria makes long-term strain-specific immunity highly improbable, thus rendering models requiring lifelong strain-specific immunity unlikely to be of relevance in most epidemiological contexts.

Journal Article↗

PubMed1992

Predicting post-hospital discharge health care costs.

Patients in this study represented an important group for health services research; their postdischarge costs were high, resulted from readmissions (especially for nonelective reasons), and were incurred by a minority of patients. Moreover, intensive interventions delivered by ambulatory care providers has the potential to reduce overall costs if patients at highest risk for readmission could be identified prospectively (Smith et al., 1988; Weinberger et al., 1988). We developed a model to predict post-hospital discharge costs in these patients using strategies to maximize their predictive capability. Although the model appeared to account for more variance in costs than currently available models in the derivation set, its performance in the validation set, albeit statistically significant, was disappointing. Because we considered a broad array of predictors, expanding the number of patient-oriented variables may not be fruitful. Instead, future research may need to consider more homogenous subgroups of patients in whom specific laboratory tests would have clinical significance; variance in providers' behaviors; and studies in health maintenance organizations, where control over resource utilization may make costs more predictable. Finally, empirically derived models must be tested in an independent sample. Without validating predictive models, the models' ability to predict health care costs may be overestimated.

Ambulatory Care↗

PubMed1996

Depressive thinking: changes in schematic mental models of self and world.

Alternative explanations for the changes in thinking associated with depression were examined. Depressive thinking could reflect a generalized increase in accessibility of negative constructs and memories, previously associated with depression. Alternatively, depressive thinking could reflect changes at a more generic level of cognitive representation, related to schematic mental models. To investigate contrasting predictions from these two explanations, depressed patients and non-depressed controls completed sentence stems involving social approval or personal achievement e.g. 'If I could always be right then others would-me'. Construct accessibility views predict that depression will be associated with more negative completions (e.g. 'dislike'). By contrast, the schematic model view predicts patients may give more positive completions (e.g. 'like'). This is because schematic models reflect inter-relationships between constructs, and, it is suggested, depression is associated with use of schematic mental models that imply closer dependence of personal worth/acceptance on success/approval than the models used in the non-depressed state. Predictions from the schematic model view were supported, confirming previous findings. Results suggest that depressive thinking reflects changes in the high level mental models used to interpret experience.

Adolescent↗

PubMed1997

The mechanism of respiratory rhythm generation during constant flow assisted mechanical ventilation in the decerebrated dog.

In awake human subjects input from the forebrain has significant effects on the respiratory pattern during assisted (AMV) and controlled (CMV) mechanical ventilation. The hypothesis in this animal study was that if the influence from the forebrain is eliminated, the respiration during AMV and that during CMV is controlled by the same mechanism. Fifteen decerebrated and tracheostomized dogs were subjected to CMV with a variety of combinations of tidal volume and frequency. The respiratory rhythm during CMV was simulated by a mathematical model composed of the central respiratory activity and inputs from pulmonary receptors. During AMV, the respiratory cycle duration was prolonged, and this was found to be the summated effect of prolonged Ttg (ventilator trigger period) and shortened Tinf (lung inflation period). When these changes in Ttg and Tinf were included, the model for CMV predicted respiratory changes during AMV. We concluded that the basic mechanism controlling AMV and CMV may be the same.

Animals↗

PubMed1990

Influence of reflow ventricular fibrillation and electrical defibrillation on infarct size in a canine preparation of myocardial infarction.

STUDY OBJECTIVE - The aim of the study was to investigate the influence of reflow ventricular fibrillation and electrical defibrillation on infarct size in a model of myocardial ischaemia. DESIGN - Myocardial ischaemia was induced in an open chest canine model by occluding the left coronary artery for 2 h. This was followed by 6 h reperfusion. The influence of reflow fibrillation and internal electric defibrillation on infarct size was investigated and compared to dogs which did not develop fibrillation. Infarct size and its major determinants, rate-pressure product (RPP), area at risk (AR), and collateral flow (MBF), were measured and their relationships studied in the two situations, using uni- and multilinear regression analysis. SUBJECTS - 21 adult mongrel dogs of either sex were used in the studies, which were done under pentobarbitone anaesthesia. Two were excluded because they developed ventricular fibrillation soon after coronary occlusion, and one did not survive reflow ventricular fibrillation. Of the remaining 18 dogs, six developed reflow ventricular fibrillation and were compared to the control group of 12 which did not develop fibrillation. MEASUREMENTS and RESULTS - A mean of 70.8(SEM 18.7) joules was required to revive the six dogs with reflow ventricular fibrillation. Difference in mean infarct size in the two groups did not reach significance [49.1(4.4) in fibrillation group v 38(6.2) in the controls]. The multiple linear regression model in the control group accounted for 91% of the variation in infarct size (IS): IS = -3.4 + 0.49 (AR) -21.8 (MBF) + 0.025 (RPP). The equation was not modified by including the reflow fibrillation dogs: IS = -3.1 + 0.52 (AR) - 19 (MBF) + 0.02 (RPP). Ischaemic determinants of infarct size in the reflow fibrillation dogs were computed in the control group equation to compare the infarct size predicted by the model to the measured infarct size in each individual dog in the reflow fibrillation group. There was no significant difference between the means: 12.9(2.9)% (predicted) v 14.9(2.5)% (measured). CONCLUSIONS - In this model of myocardial infarction, reflow ventricular fibrillation and low energy internal electric shocks do not damage the myocardium at risk significantly.

Animals↗