Biomedical subjects

Lukas Schaupp

Publications and source records attributed to Lukas Schaupp.

6 recordsLinked to original sources

PubMed2006

Fiber-optic flow-through sensor for online monitoring of glucose.

A new microdialysis-based glucose-sensing system with an integrated fiber-optic hybrid sensor is presented. Design and dimensions of the cell are adapted for its coupling with commercially available microdialysis techniques, thereby providing a new system for continuous glucose monitoring. The glucose level is detected via oxygen consumption which occurs as a consequence of enzymatic reaction between immobilized glucose oxidase and glucose. The use of gas-permeable Tygon tubing ensures complete and constant air-saturation of the measuring fluid in the cell. Nevertheless, a reference oxygen optode is used to detect and to compensate response changes caused by events like bacterial growth, temperature fluctuations, or failure of the peristaltic pump. In contrast to widely used electrochemical sensors, the response of the microdialysis-based fiber-optic glucose sensor is highly selective, making this sensor approach particularly advantageous for continuous glucose monitoring of patients in intensive care units. The effects of flow rate, pH, temperature, and common interferences on the sensor response are presented and discussed in detail. The sensor is evaluated in vitro using a 3-day continuous test in glucose-spiked plasma. The ability to measure glucose in humans is demonstrated by coupling the flow-through cell and commercially available microdialysis catheter CMA60. A 24-h monitoring test using this setup is successfully applied to a healthy volunteer.

Enzymes, Immobilized↗

PubMed2006

Clinical evaluation of alternative-site glucose measurements in patients after major cardiac surgery.

OBJECTIVE: Tight glycemic control improves outcome in critically ill patients but requires frequent glucose measurements. Subcutaneous adipose tissue (SAT) has been characterized as promising for glucose monitoring in diabetes, but it remains unknown whether it can also be used as an alternative site in critically ill patients. The present study was performed to clinically evaluate the relation of glucose in SAT compared with arterial blood in patients after major cardiac surgery. RESEARCH DESIGN AND METHODS: Forty critically ill patients were investigated at two clinical centers after major cardiac surgery. Arterial blood and SAT microdialysis samples were taken in hourly intervals for a period of up to 48 h. The glucose concentration in dialysate was calibrated using a two-step approach, first using the ionic reference technique to calculate the SAT glucose concentration (SATg) and second using a one-point calibration procedure to obtain a glucose profile comparable to SAT-derived blood glucose (BgSAT). Clinical validation of the data was performed by introducing data analysis based on an insulin titration algorithm. RESULTS: Correlation between dialysate glucose and blood glucose (median 0.80 [interquartile range 0.68-0.88]) was significantly improved using the ionic reference calibration technique (SATg vs.blood glucose 0.90 [0.83-0.94]; P < 0.001). Clinical evaluation of the data indicated that 96.1% of glucose readings from SAT would allow acceptable treatment according to a well-established insulin titration protocol. CONCLUSIONS: The results indicate good correlation between SATg and blood glucose in patients after major cardiac surgery. Clinical evaluation of the data suggests that with minor limitations, glucose from SAT can be used to establish tight glycemic control in this patient group.

Aged↗

PubMed2005

Insulin kinetics in type-I diabetes: continuous and bolus delivery of rapid acting insulin.

We investigated insulin lispro kinetics with bolus and continuous subcutaneous insulin infusion (CSII) modes of insulin delivery. Seven subjects with type-1 diabetes treated by CSII with insulin lispro have been studied during prandial and postprandial conditions over 12 hours. Eleven alternative models of insulin kinetics have been proposed implementing a number of putative characteristics. We assessed 1) the effect of insulin delivery mode, i.e., bolus or basal, on the insulin absorption rate, the effects of 2) insulin association state and 3) insulin dose on the rate of insulin absorption, 4) the remote insulin effect on its volume of distribution, 5) the effect of insulin dose on insulin disappearance, 6) the presence of insulin degradation at the injection site, and finally 7) the existence of two pathways, fast and slow, of insulin absorption. An iterative two-stage parameter estimation technique was used. Models were validated through assessing physiological feasibility of parameter estimates, posterior identifiability, and distribution of residuals. Based on the principle of parsimony, best model to fit our data combined the slow and fast absorption channels and included local insulin degradation. The model estimated that 67(53-82)% [mean (interquartile range)] of delivered insulin passed through the slow absorption channel [absorption rate 0.011(0.004-0.029) min(-1)] with the remaining 33% passed through the fast channel [absorption rate 0.021(0.011-0.040) min(-1)]. Local degradation rate was described as a saturable process with Michaelis-Menten characteristics [VMAX = 1.93(0.62 - 6.03) mU min(-1), KM = 62.6(62.6 - 62.6) mU]. Models representing the dependence of insulin absorption rate on insulin disappearance and the remote insulin effect on its volume of distribution could not be validated suggesting that these effects are not present or cannot be detected during physiological conditions.

Adult↗

PubMed2004

Nonlinear model predictive control of glucose concentration in subjects with type 1 diabetes.

A nonlinear model predictive controller has been developed to maintain normoglycemia in subjects with type 1 diabetes during fasting conditions such as during overnight fast. The controller employs a compartment model, which represents the glucoregulatory system and includes submodels representing absorption of subcutaneously administered short-acting insulin Lispro and gut absorption. The controller uses Bayesian parameter estimation to determine time-varying model parameters. Moving target trajectory facilitates slow, controlled normalization of elevated glucose levels and faster normalization of low glucose values. The predictive capabilities of the model have been evaluated using data from 15 clinical experiments in subjects with type 1 diabetes. The experiments employed intravenous glucose sampling (every 15 min) and subcutaneous infusion of insulin Lispro by insulin pump (modified also every 15 min). The model gave glucose predictions with a mean square error proportionally related to the prediction horizon with the value of 0.2 mmol L(-1) per 15 min. The assessment of clinical utility of model-based glucose predictions using Clarke error grid analysis gave 95% of values in zone A and the remaining 5% of values in zone B for glucose predictions up to 60 min (n = 1674). In conclusion, adaptive nonlinear model predictive control is promising for the control of glucose concentration during fasting conditions in subjects with type 1 diabetes.

Blood Glucose↗

PubMed2004

Closing the loop: the adicol experience.

The objective of the project Advanced Insulin Infusion using a Control Loop (ADICOL) was to develop a treatment system that continuously measures and controls the glucose concentration in subjects with type 1 diabetes. The modular concept of the ADICOL's extracorporeal artificial pancreas consisted of a minimally invasive subcutaneous glucose system, a handheld PocketPC computer, and an insulin pump (D-Tron, Disetronic, Burgdorf, Switzerland) delivering subcutaneously insulin lispro. The present paper describes a subset of ADICOL activities focusing on the development of a glucose controller for semi-closed-loop control, an in silico testing environment, clinical testing, and system integration. An incremental approach was adopted to evaluate experimentally a model predictive glucose controller. A feasibility study was followed by efficacy studies of increasing complexity. The ADICOL project demonstrated feasibility of a semi-closed-loop glucose control during fasting and fed conditions with a wearable, modular extracorporeal artificial pancreas.

Blood Glucose↗

PubMed2003

Assessment of transcapillary glucose exchange in human skeletal muscle and adipose tissue.

We studied the kinetics of glucose exchange between plasma and interstitial fluid (ISF) in human skeletal muscle and adipose tissue under fasting conditions. Five normal human subjects received an intravenous [6,6-2H2]glucose infusion in a prime-continuous fashion. During the tracer infusion, the open-flow microperfusion technique was employed to frequently sample ISF from quadriceps muscle and subcutaneous adipose tissue. The tracer glucose kinetics observed in muscle and adipose tissue ISF were found to be well described by a capillary-tissue exchange model. As a measure of transcapillary glucose exchange efficiency, the 95% equilibrium time was calculated from the identified model parameters. This time constant was similar for skeletal muscle and adipose tissue (28.6 +/- 3.2 vs. 26.8 +/- 3.6 min; P = 0.60). Furthermore, we found that the (total) interstitial glucose concentration was significantly lower (P < 0.01) in muscle (3.32 +/- 0.46 mmol/l) and adipose tissue (3.51 +/- 0.17 mmol/l) compared with arterialized plasma levels (5.56 +/- 0.13 mmol/l). Thus the observed gradients and dynamic relationships between plasma and ISF glucose in muscle and adipose tissue provide evidence that transcapillary exchange of glucose is limited in these two tissues under fasting conditions.

Adipose Tissue↗