Visualising the knowledge structure and evolution of wearable device research

In recent years, the literature associated with wearable devices has grown rapidly, but few studies have used bibliometrics and a visualisation approach to conduct deep mining and reveal a panorama of the wearable devices field. To explore the foundational knowledge and research hotspots of the wearable devices field, this study conducted a series of bibliometric analyses on the related literature, including papers' production trends in the field and the distribution of countries, a keyword co-occurrence analysis, theme evolution analysis and research hotspots and trends for the future. By conducting a literature content analysis and structure analysis, we found the following: (a) The subject evolution path includes sensor research, sensitivity research and multi-functional device research. (b) Wearable device research focuses on information collection, sensor materials, manufacturing technology and application, artificial intelligence technology application, energy supply and medical applications. The future development trend will be further studied in combination with big data analysis, telemedicine and personalised precision medical application.

A Simulation Study on a Self-Tuning Portable Controller of Blood Glucose

A self-tuning, nonlinear controller was developed to drive portable or implantable micro-pumps for blood glucose control in diabetic subjects. The parameter estimation is based on a recursive least-square algorithm applied to a discrete time simplified mathematical model of the glucose system; the controller, which is integrated with the estimator, uses an-extended minimum-variance method. The software was designed to drive a micro-controller wearable unit, operating with different kinds of glucose sensors, in order to perform chemical and biological experimentations. Some strategies were introduced to avoid hypoglycaemia, even tolerating a reduction in control speed and accuracy. The whole system was tested in a simulation study, performed on a mathematical model implemented on a personal computer. The tests were performed while simulating different controller structures and settings, and patient responses. They showed a satisfactory control behaviour, mostly as far as stability and robustness are concerned, in all simulated conditions.

A Mathematical Model Describing the Glycemic Response of Diabetic Patients to Meal and i.v. Infusion of Insulin

Nine type 1 diabetic patients were studied for 24 hours. Düring this period they were given three calibrated meals. The glycemia was feedback-controlled by means of an artificial pancreas. The blood concentration of glucose and the infusion speed of the insulin were measured every minute. The experimental data referring to each of the three meals were used to estimate the Parameters of a mathematical model suitable for describing the glycémie response of diabetic patients at meals and at the i. v. infusion of exogenous insulin. From the estimate a marked dispersion of the Parameters was found, both interindividual and intraindividual. Nevertheless the models thus obtained seem to be usable for the synthesis of a feedback controller, especially in view of creating a portable artificial pancreas that now seems possible owing to the realization (so far experimental) of sufficiently reliable glucose concentration sensors.

A Survey of Insulin-Dependent Diabetes-Part II: Control Methods

We survey blood glucose control schemes for insulin-dependent diabetes therapies and systems. These schemes largely rely on mathematical models of the insulin-glucose relations, and these models are typically derived in an empirical or fundamental way. In an empirical way, the experimental insulin inputs and resulting blood-glucose outputs are used to generate a mathematical model, which includes a couple of equations approximating a very complex system. On the other hand, the insulin-glucose relation is also explained from the well-known facts of other biological mechanisms. Since these mechanisms are more or less related with each other, a mathematical model of the insulin-glucose system can be derived from these surrounding relations. This kind of method of the mathematical model derivation is called a fundamental method. Along with several mathematical models, researchers develop autonomous systems whether they involve medical devices or not to compensate metabolic disorders and these autonomous systems employ their own control methods. Basically, in insulin-dependent diabetes therapies, control methods are classified into three categories: open-loop, closed-loop, and partially closed-loop controls. The main difference among these methods is how much the systems are open to the outside people.

Clinical validation of a new control-oriented model of insulin and glucose dynamics in subjects with type 1 diabetes

BACKGROUND

The development of an artificial pancreas requires an accurate representation of diabetes pathophysiology to create effective and safe control systems for automatic insulin infusion regulation. The aim of the present study is the assessment of a previously developed mathematical model of insulin and glucose metabolism in type 1 diabetes and the evaluation of its effectiveness for the development and testing of control algorithms.

METHODS

Based on the already existing "minimal model" a new mathematical model was developed composed of glucose and insulin submodels. The glucose model includes the representation of peripheral uptake, hepatic uptake and release, and renal clearance. The insulin model describes the kinetics of exogenous insulin injected either subcutaneously or intravenously. The estimation of insulin sensitivity allows the model to personalize parameters to each subject. Data sets from two different clinical trials were used here for model validation through simulation studies. The first set had subcutaneous insulin injection, while the second set had intravenous insulin injection. The root mean square error between simulated and real blood glucose profiles (G(rms)) and the Clarke error grid analysis were used to evaluate the system efficacy.

RESULTS

Results from our study demonstrated the model's capability in identifying individual characteristics even under different experimental conditions. This was reflected by an effective simulation as indicated by G(rms), and clinical acceptability by the Clarke error grid analysis, in both clinical data series.

CONCLUSIONS

Simulation results confirmed the capacity of the model to faithfully represent the glucose-insulin relationship in type 1 diabetes in different circumstances.

Control oriented model of insulin and glucose dynamics in type 1 diabetics

The aim of the study was to realize a mathematical model of insulin-glucose relationship in type I diabetes and test its effectiveness for the design of control algorithms in external artificial pancreas. A new mathematical model, divided into glucose and insulin sub-models, was developed from the so-called "minimal model". The key feature is the representation of insulin sensitivity so as to permit the personalisation of the parameters. Real-time applications are based on an insulin standardised model. Clinical data were used to estimate model parameters. Root mean square error between simulated and real blood glucose profiles (G(rms)) was used to evaluate system efficacy. Results from parameter estimation and insulin standardisation showed a good capability of the model to identify individual characteristics. Simulation results with a G(rms) 1.30 mmol/l in the worst case testified the capacity of the model to accurately represent glucose-insulin relationship in type 1 diabetes allowing self tuning in real time.

The physiologic cipher at altitude: telemedicine and real-time monitoring of climbers on Mount Everest

Advanced wearable biosensors for vital-signs monitoring (physiologic cipher) are available to improve quality of healthcare in hospital, nursing home, and remote environments. The objective of this study was to determine reliability of vital-signs monitoring systems in extreme environments. Three climbers were monitored 24 hours while climbing through Khumbu Icefall. Data were transmitted to Everest Base Camp (elevation 17,800 feet) and retransmitted to Yale University via telemedicine. Main outcome measures (location, heart rate, skin temperature, core body temperature, and activity level) all correlated through time-stamped identification. Two of three location devices functioned 100% of the time, and one device failed after initial acquisition of location 75% of the time. Vital-signs monitors functioned from 95%-100% of the time, with the exception of one climber whose heart-rate monitor functioned 78% of the time. Due to architecture of automatic polling and data acquisition of biosensors, no climber was ever without a full set of data for more than 25 minutes. Climbers were monitored continuously in real-time from Mount Everest to Yale University for more than 45 minutes. Heart rate varied from 76 to 164 beats per minute, skin temperature varied from 5 to 10 degrees C, and core body temperature varied only 1-3 degrees C. No direct correlation was observed among heart rate, activity level, and body temperature, though numerous periods suggested intense and arduous activity. Field testing in the extreme environment of Mount Everest demonstrated an ability to track in real time both vital signs and position of climbers. However, these systems must be more reliable and robust. As technology transitions to commercial products, benefits of remote monitoring will become available for routine healthcare purposes.

Glucose monitoring: state of the art and future possibilities

This article reviews the development of glucose monitoring techniques and approaches during the last decade. The predominance of the electrochemical measuring principles reported in the literature makes them a focus of this work. Biosensors are still in the main stream of the research interest of most teams due to their high selectivity for glucose determination. Systematization and classification of the glucose monitoring principles and types of glucose sensors is shown. The review gives a brief description of the basic operational principles of the most popular types of glucose biosensors, providing an enhanced bibliography of the original works of the main groups in establishing or significantly contributing to the development of the particular type of glucose biosensor. Different design approaches are overviewed including needle-type sensors, sensors for chronical implantation and the combination of the glucose biosensors with microdialysis sampling technique. The authors approach for replacing of the spent enzyme and thus recharging the sensor in situ while implanted is widely discussed. This approach provides a way to increase the lifespan of the system and ultimately, it could lead to rare transcutaneous interventions for refilling of the implanted sensor.