Golo von Basum

Fast exponential fitting algorithm for real-time instrumental use

We report on a very fast fitting algorithm for single exponential functions which is based on the method of successive integration. The algorithm corrects the systematic error of trapezoidal integration. The new algorithm needs only 150 μs for a dataset of 1536 points and is around 700 times faster than the nonlinear Levenberg–Marquardt fit provided by LABVIEW. This makes it suitable for real-time instrumental use. Beside the better time resolution, the acceleration allows more averaging, which leads to higher precision. In our experiment instrumental sensitivity was improved by a factor of 3.7.

Parts per trillion sensitivity for ethane in air with an optical parametric oscillator cavity leak-out spectrometer

Spectroscopic detection of ethane in the 3-microm wavelength region was performed by means of a cw optical parametric oscillator and cavity leak-out. We achieved a minimum detectable absorption coefficient of 1.6 x 10(-10) cm 1/square root of Hz, corresponding to an ethane detection limit of 6 parts per trillion/square root of Hz. For 3-min integration time the detection limit was 0.5 parts per trillion. The levels are to our knowledge the best demonstrated so far. These frequency-tuning capabilities facilitated multigas analysis with simultaneous monitoring of ethane, methane, and water vapor in human breath.

Future acceptance of an artificial pancreas in adults with type 1 diabetes.

BACKGROUND The purpose of this study was to examine future acceptance of an artificial pancreas (AP) and its perceived usefulness, ease of use, and trust in the device. METHODS A questionnaire, based on the Technology Acceptance Model, was developed to examine future acceptance with its determinants and intention to use the AP. One hundred thirty-two patients with diabetes type 1 treated with insulin pump therapy completed the questionnaire. Using factor analysis and reliability analysis, the number of items was reduced from 34 to 15. RESULTS The response rate was 66%. The subjects had a mean age of 43 years, and 34% were male. Almost 75% had the intention to use an AP. There were high scores on perceived usefulness (expected improvement of glucose control: 35.6% moderately agreed and 53% strongly agreed), perceived ease of use (expectation that the AP can be easily handled: 33.3% moderately agreed and 53.8% strongly agreed), and trust (administration of correct insulin dose and reliability of glucose measurement: 40.9% and 38.9% moderately agreed, whereas 32.6% and 28.2% strongly agreed, respectively). CONCLUSIONS A newly developed questionnaire examining the acceptance of an AP indicated that most patients with continuous subcutaneous insulin infusion-treated type 1 diabetes have the intention to use an AP system and have a positive attitude toward perceived usefulness, ease of use, and trust.

Patients' Perception and Future Acceptance of an Artificial Pancreas

Background: Little is known of patient acceptance of an artificial pancreas (AP). The purpose of this study was to investigate future acceptance of an AP and its determinants. Methods: Patients with type 1 diabetes treated with insulin pump therapy were interviewed using questions based on the technology acceptance model and completed the diabetes treatment and satisfaction questionnaire (DTSQ). Results: Twenty-two adults with type 1 diabetes participated. Half of the patients were followed in a university hospital, and the others were under treatment in an affiliated teaching hospital. Half of the patients were male. The mean DTSQ score was 29 (range 23–33). The AP was perceived as likely to be useful. Perceived advantages were a stable glucose regulation, less need for self-monitoring of blood glucose, relief of daily concerns, and time saving. Participants were confident in their capability to use the system. Although many participants (58%) had been reluctant to start continuous subcutaneous insulin infusion, the majority (79%) felt they would have no barriers to start using the AP. Trust in the AP was related to the quality of glucose control it would provide. Almost everyone expressed the intention to use the new system when available, even if it would initially not cover 24/24 hours. Conclusion: The overall attitude on the AP was positive. Intention to use was dependent on trust in the AP, which was related to the quality of glucose control provided by the AP.

Quantifying the Composition of Human Skin for Glucose Sensor Development

Background: Glucose is heterogeneously distributed within human skin. In order to develop a glucose measurement method for human skin, both a good quantification of the different compartments of human skin and an understanding of glucose transport processes are essential. This study focused on the composition of human skin. In addition, the extent to which intersubject variability in skin composition alters glucose dynamics in human skin was investigated. Methods: To quantify the composition of the three layers of human skin—epidermis, dermis, and adipose tissue—cell and blood vessel volumes were calculated from skin biopsies. These results were combined with data from the literature. The composition was applied as input for a previously developed computational model that calculates spatiotemporal glucose dynamics in human skin. The model was used to predict the physiological effects of intersubject variability in skin composition on glucose profiles in human skin. Results: According to the model, the lag time of glucose dynamics in the epidermis was sensitive to variation in the volumes of interstitial fluid, cells, and blood of all layers. Data showed most variation/uncertainty in the volume composition of the adipose tissue. This variability mainly influences the dynamics in the adipose tissue. Conclusions: This study identified the intersubject variability in human skin composition. The study shows that this variability has significant influence on the glucose dynamics in human skin. In addition, it was determined which volumes are most critical for the quantification and interpretation of measurements in the different layers.

Is exhaled carbon monoxide level associated with blood glucose level? A comparison of two breath analyzing methods

The level of exhaled carbon monoxide (eCO) is considered a marker of oxidative stress in diabetes. Previous findings indicated that eCO levels correlated with blood glucose level. The aim of this work was to apply and compare two independent analyzing methods for eCO after oral glucose administration. Glycemia, eCO, and exhaled hydrogen were measured before and after oral administration of glucose. Six healthy nonsmoking volunteers participated. For eCO analysis, we used two methods: a commercially available electrochemical sensor, and a high-precision laser spectrometer developed in our laboratory. The precision of laser-spectroscopic eCO measurements was two orders of magnitude better than the precision of the electrochemical eCO measurement. eCO levels measured by laser spectrometry after glucose administration showed a decrease of 4.1%+/-1.5% compared to the baseline (p<0.05). Changes in the eCO measured by the electrochemical sensor were not significant (p=0.08). Exhaled hydrogen levels increased by 40% within the first 10 min after glucose administration (p<0.05). The previous finding that the glycemia increase after glucose administration was associated with a significant increase in eCO concentrations was not confirmed. We propose that previous eCO measurements with electrochemical sensors may have been affected by cross sensitivity to hydrogen.

Exercise in Closed-Loop Control: A Major Hurdle

Background: People with type 1 diabetes mellitus (T1DM) are at risk for exercise-induced hypoglycemia. Prevention of such hypoglycemia in a closed-loop setting is a major challenge. Markers for automated detection of physical activity could be heart rate (HR) and body acceleration counts (AC). Correlations between HR, AC, and glucose concentrations before and after moderate intensity exercise were examined in T1DM patients during open-loop control. Method: Eleven T1DM subjects treated with an insulin pump performed moderate intensity exercise of 30 min. Glucose profiles, insulin concentrations, HR, and acceleration were measured. Results: Mean (range) glucose decrease during exercise was 1.4 (0 to 3.3) mmol/liter. The mean increase in HR was 45.2 beats per minutes (15 to 106 bpm). Mean increase in AC was 18,000 (3,000 to 25,000). No correlations were seen between the glucose drop and HR or AC. A trend was observed between the increase in HR and increase in AC. Conclusion: Moderate intensity exercise resulted in increased HR and body AC while it decreased glucose concentrations but, in this real-time setting, no association could be demonstrated between the glucose decrease and increase in HR or AC.

Medical Trace Gas Detection by Means of Mid-Infrared Cavity Leak-Out Spectroscopy

Ambient air and the human breath both contain many different volatile organic and inorganic compounds. Most of them are present in very low concentrations. The analysis of these trace gases leads in case of ambient air to a better understanding of the atmospheric chemistry and in the case of breath tests to a deeper knowledge of the physiological processes in the human body. Amongst other sources these compounds are produced in the human organism and find their way via the blood through the lungs into the human breath. Most of the volume fractions of these trace gases are on the order of some ppb (parts per billion: 1:109) down to several ppt (parts per trillion: 1:1012). This shows the need for ultra sensitive analytical methods for the in-vivo monitoring of human breath, which helps to understand various physiological and pathophysiological processes in the human organism.