Impact of sensor and measurement timing errors on model-based insulin sensitivity

peer reviewe

Undergraduate Heat Exchanger Laboratory

Heat exchangers are a fundamental part of many industrial and household devices, and a focus in the United States Military Academy at West Point’s undergraduate heat transfer course within the school’s Department of Civil and Mechanical Engineering. Recently, the department expanded laboratory capabilities to enhance student learning through hands-on experimentation. Prior to this project, a heat exchanger laboratory did not exist for student use, so a new apparatus was designed, developed, built, tested, and will be implemented as a laboratory experience in West Point’s heat transfer course. The experimental apparatus includes a fan-cooled heat sink, a high-efficiency water heater, two pumps for water circulation, and numerous valves to change both the direction and route of the flows. This design allows students to test three types of heat exchangers: shell-in-tube, concentric, and flat plate. These devices allow students to evaluate parallel-flow, counter-flow, and cross-flow heat exchangers. The test section is instrumented with flow meters for the hot and cold flows as well as thermocouples at the entrance and exit of each heat exchanger. As part of this laboratory experience, students measure, collect, and analyze data, compare experimental results to theory, and assess error and uncertainty. This heat exchanger laboratory provide realistic, hands-on experience with experimental apparatus, laboratory procedure, instrumentation, and engineering technicians, all of which help students gain physical understanding of the thermal-fluids concepts

Model-Based Decision Support in Glycaemic Control

Model-based decision support relies on a series of mathematical models and methods to convert raw clinical data into actionable recommendations. High clinical burden associated with measurement, and clinically significant outcomes, make glycaemic control an area where considerable benefit is possible. However, few glycaemic control protocols have been successful in critical care, and fewer exist for outpatient management of diabetes. Challenges faced include high levels of uncertainty and noise, limited measurements, and risk of iatraogenic low blood glucose events. This thesis aims to develop a successful glycaemic control framework, STAR, beyond the critical care environment, and set the stage for an outpatient glycaemic control protocol that individuals with diabetes can use to inform their day-to-day glucose management decisions. To achieve this goal, appropriate models and methods are developed, and validated against both clinical and in-silico data

Model-based glycemic control in critical care

http://www.ncbme.ugent.be/event.php?id=15 I have pdf scans and proceedings bookModel-based glycemic control uses a physiological model and patient-specific parameters to tailor interventions to each patient, overcoming significant variability within and between patients. STAR is a successful model-based protocol that has been developed and tested collaboratively in New Zealand, Belgium and Hungary

Development and Pilot Trial Results of Stochastic Targeted (STAR) Glycemic Control in a Medical ICU

peer reviewe

Detection of low chemical concentrations by cavity ring-down in an evanescently coupled fused optical fibre taper

A novel sensor for detecting very low concentrations of chemicals in water and other liquids is presented. A cavity ring-down spectrometer has been developed that can measure chemicals in solution in a harsh environment. The high Q Fabry Perot cavity is fabricated in an optical fibre with high reflectivity mirrors on each end. The cavity contains a fused fibre taper, with very low intrinsic loss, for coupling light in the cavity evanescently into a smart surface layer that is bound on to the fibre surface. Small changes in the absorption are detected by changes in the ring-down time of the resonant cavity. The low loss cavity results in ring down times of 1μs for a 2 m cavity, which is equivalent to 100 passes through the smart surface. The ring down time provides a very accurate measure of absorbance because it is independent of source and detector drift and the fibre cavity is unaffected by changes in temperature, vibration or bending. Absorption changes of 5x10-5 dB can be detected with the current configuration and further improvements can be achieved by optimisation leading to detection of atto-molar chemical concentrations

Improving Safety of Glucose Control in Intensive Care using Virtual Patients and Simulated Clinical Trials

ABSTRACT Despite the potential clinical benefits of normalizing blood glucose in critically ill patients, the risk of hypoglycemia is a major barrier to widespread clinical adoption of accurate glycemic control. To compare five glucose control protocols, a validated insulin-glucose system model was employed to perform simulated clinical trials. STAR, SPRINT, UNC, Yale and Glucontrol protocols were assessed over a medical-surgical intensive care unit patient cohort. Results were interpreted separately for patients with low to high sensitivity to insulin, and low to high variability in metabolic state. STAR and SPRINT provided good glucose control with risk of severe hypoglycemia less than 0.05% across all patient groups. UNC also achieved good control for patients with low and medium levels of insulin sensitivity (SI), but risk of severe hypoglycemia was raised for patients with high SI. Glucontrol showed degradation of performance for patients with high metabolic variability

Uporaba krivulje plastičnega tečenja v numeričnih simulacijah

V prispevku je obravnavano določevanje krivulje plastičnega tečenja jeklene pločevine pri velikih deformacijah. Uporabljena sta dva računska postopka, obema pa kot eksperimentalna osnova služi klasični natezni preizkus. Pri prvem postopku krivuljo plastičnega tečenja aproksimiramo s pomočjo t.i. Ludvikovega zakona ter tako dobljeno krivuljo se ekstrapoliramo na območje velikih deformacij. Drugi postopek temelji na inverzni identifikaciji, kjer krivuljo plastičnega tečenja pri velikih deformacijah okarakteriziramo na osnovi meritev nateznega preizkusa po nastanku lokalne zožitve na nateznem preizkušancu. Značilnosti obeh postopkov so obrazložene na primerih računalniskih simulacij nateznega preizkusa in globokega vleka. Že v primeru simulacije nateznega preizkusa metoda inverzne identifikacije prekaša metodo aproksimacije z Ludvikovim zakonom, primer simulacije globokega vleka pa nazorno prikaže, kako uporaba neprimerne krivulje plastičnega tečenja vodi do napačnih sklepov in napovedi.A comparison of two approaches used in the yield curve characterization of thesame material is given in the paper. The first approach is commonly used Ludwig\u27s law with the extension over large strains based on the pre-necking response of a tensile test specimen, whereas the second approach is inverse identification which is based on the post-necking behaviour of the same tensile test specimen. Features of both approaches are examined in the tensile test and deep drawing simulations. In the tensile test simulation the inverse identification method proved to be superior over Ludwig\u27s law. The deep drawing simulation demonstrates how inappropriate yield curve usage leads to wrong predictions

STAR Development and Protocol Comparison

"(c) 2012 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works."Accurate glycemic control (AGC) is difficult due to excessive hypoglycemia risk. Stochastic TARgeted (STAR) glycemic control forecasts changes in insulin sensitivity to calculate a range of glycemic outcomes for an insulin intervention, creating a risk framework to improve safety and performance. An improved, simplified STAR framework was developed to reduce light hypoglycemia and clinical effort, while improving nutrition rates and performance. Blood glucose (BG) levels are targeted to 80 – 145mg/dL, using insulin and nutrition control for 1-3 hour interventions. Insulin changes are limited to +3U/hour and nutrition to ±30% of goal rate (minimum 30%). All targets and rate change limits are clinically specified and generalizable. Clinically validated virtual trials were run on using clinical data from 371 patients (39,841hours) from the SPRINT cohort. Cohort and per-patient results are compared to clinical SPRINT data, and virtual trials of three published protocols. Performance was measured as time within glycemic bands, and safety by patients with severe (BG<40mg/dL) and mild (%BG<72mg/dL) hypoglycemia. Pilot trial results from the first 10 patients (1,458 hours) are included to support the in-silico findings. In both virtual and clinical trials, mild hypoglycemia was below 1% versus 4% for SPRINT. Severe hypoglycemia was reduced from 14 (SPRINT) to 6 (STAR), and 0 in the pilot trial. AGC was tighter than both SPRINT clinical data and in silico comparison protocols, with 91% BG within the specified target (80–145mg/dL) in virtual trials and 93.4% in pilot trials. Clinical effort (measurements) was reduced from 16.2/day to 12.0/day (13.9/day in pilot trials). This STAR framework provides safe, accurate glycemic control with significant reductions in hypoglycemia and clinical effort due to stochastic forecasting of patient variation – a unique risk-based approach. Initial pilot trials validate the in silico design methods and resulting protocol, all of which can be generalized to suit any given clinical environment

Interstitial insulin kinetic parameters for a 2-compartment insulin model with saturable clearance

Glucose-insulin system models are commonly used for identifying insulin sensitivity. With physiological, 2-compartment insulin kinetics models, accurate kinetic parameter values are required for reliable estimates of insulin sensitivity. This study uses data from 6 published microdialysis studies to determine the most appropriate parameter values for the transcapillary diffusion rate (nI) and cellular insulin clearance rate (nC).The 6 studies (12 data sets) used microdialysis techniques to simultaneously obtain interstitial and plasma insulin concentrations. The reported plasma insulin concentrations were used as input and interstitial insulin concentrations were simulated with the interstitial insulin kinetics sub-model. These simulated results were then compared to the reported interstitial measurements and the most appropriate set of parameter values was determined across the 12 data sets by combining the results. Interstitial insulin kinetic parameters values nI=nC=0.0060min-1 were shown to be the most appropriate. These parameter values are associated with an effective, interstitial insulin half-life, t1/2=58min, within the range of 25-130min reported by others. © 2014 Elsevier Ireland Ltd