Non-invasive glucose monitoring in patients with diabetes: A novel system based on impedance spectroscopy

The aim of this work was to evaluate the performance of a novel non-invasive continuous glucose-monitoring system based on impedance spectroscopy (IS) in patients with diabetes. Ten patients with type 1 diabetes (mean+/-S.D., age 28+/-8 years, BMI 24.2+/-3.2 kg/m(2) and HbA(1C) 7.3+/-1.6%) and five with type 2 diabetes (age 61+/-8 years, BMI 27.5+/-3.2 kg/m(2) and HbA(1C) 8.3+/-1.8%) took part in this study, which comprised a glucose clamp experiment followed by a 7-day outpatient evaluation. The measurements obtained by the NI-CGMD and the reference blood glucose-measuring techniques were evaluated using retrospective data evaluation procedures. Under less controlled outpatient conditions a correlation coefficient of r=0.640 and a standard error of prediction (SEP) of 45 mg dl(-1) with a total of 590 paired glucose measurements was found (versus r=0.926 and a SEP of 26 mg dl(-1) under controlled conditions). Clark error grid analyses (EGA) showed 56% of all values in zone A, 37% in B and 7% in C-E. In conclusion, these results indicate that IS in the used technical setting allows retrospective, continuous and truly non-invasive glucose monitoring under defined conditions for patients with diabetes. Technical advances and developments are needed to expand on this concept to bring the results from the outpatient study closer to those in the experimental section of the study. Further studies will not only help to evaluate the performance and limitations of using such a technique for non non-invasive glucose monitoring but also help to verify technical extensions towards a IS-based concept that offers improved performance under real life operating conditions.

Impact of environmental temperature on skin thickness and microvascular blood flow in subjects with and without diabetes

BACKGROUND

Glucose measurement from different skin areas might be influenced by changes in skin texture due to several environmental confounders. Our study was performed to investigate the effect of changes in ambient temperature on skin thickness and microvascular skin blood flow in subjects with and without diabetes at the lower forearm.

METHODS

Thirteen subjects with diabetes and seven without diabetes participated in the study. The investigations were performed in a temperature- and humidity-controlled climatic chamber (EMPA, St. Gallen, Switzerland). Starting at 25 degrees C, the environmental temperature was changed in 4 degrees C steps every 40 min. Skin thickness was measured by an ultrasonic reflection technique, and microcirculation was measured by laser Doppler fluxmetry at the lower forearm. Study participants underwent the entire procedure on up to four separate study trials.

RESULTS

Our study revealed a significantly reduced skin thickness (P<0.05) and microvascular blood flow (P<0.05) in patients with diabetes mellitus compared with controls without diabetes during the entire investigation. During declining ambient temperature a significant reduction in skin thickness (with diabetes, -0.09+/-0.13 mm; without diabetes, -0.06+/-0.11 mm; P<0.05) and microvascular blood flow (with diabetes, -41+/-49 arbitrary units; without diabetes, -46+/-51 arbitrary units; P<0.05) could be observed in both groups without significant differences between the two.

CONCLUSIONS

Although skin thickness and microvascular skin blood flow at the lower forearm were found to be reduced in patients with diabetes compared with controls without diabetes, both groups revealed comparable dynamics in skin thickness and microvascular blood flow during changes in environmental temperature.

First Experiences With a Wearable Multisensor in an Outpatient Glucose Monitoring Study, Part I: The Users' View

BACKGROUND

Extensive past work showed that noninvasive continuous glucose monitoring with a wearable Multisensor device worn on the upper arm provides useful information about glucose trends to improve diabetes therapy in controlled and semicontrolled conditions.

METHODS

To test previous findings also in uncontrolled in-clinic and outpatient conditions, a long-term study has been conducted to collect Multisensor and reference glucose data in a population of 20 type 1 diabetes subjects. A total of 1072 study days were collected and a fully on-line compatible algorithmic routine linking Multisensor data to glucose applied to estimate glucose trends noninvasively. The operation of a digital log book, daily semiautomated data transfer and at least 10 daily SMBG values were requested from the patient.

RESULTS

Results showed that the Multisensor is capable of indicating glucose trends. It can do so in 9 out of 10 cases either correctly or with one level of discrepancy. This means that in 90% of all cases the Multisensor shows the glucose dynamic to rapidly increase or at least increase.

CONCLUSIONS

The Multisensor and the algorithmic routine used in controlled conditions can track glucose trends in all patients, also in uncontrolled conditions. Training of the patient proved to be essential. The workload imposed on patients was significant and should be reduced in the next step with further automation. The feature of glucose trend indication was welcomed and very much appreciated by patients; this value creation makes a strong case for the justification of wearing a wearable.

The compensation of perturbing temperature fluctuation in glucose monitoring technologies based on impedance spectroscopy

Non-invasive glucose monitoring techniques based on impedance spectroscopy are affected by a variety of perturbing effects. In order to use the impedance as a glucose measure, these perturbing effects need to be quantified and compensated. Since effects induced by temperature fluctuations certainly rank among the severest perturbations, a clinical study was carried out to establish whether temperature, as a perturbing factor, could be compensated for in impedance spectroscopy. The results as well as a concept allowing for the compensation of perturbing temperature fluctuations are presented here. The compensation technique described is a generic approach that, in principle, can be applied to compensate most perturbation effects provided that there are now multiplicative interactions between the variable of interest (in our case the glucose) and the perturbations. The results allow for the determination of the minimum required sensitivity of an impedance spectrometer to glucose in order to be operational in home-use conditions. Furthermore, the data can be used to estimate if a universal temperature compensation can be applied or if an individual calibration is necessary. For instance, applying a universal temperature compensation and requiring an application range of +/-5 degrees C, the minimum required sensitivity of the minimum impedance and frequency in a sensor-skin RLC circuit to resolve glucose variations equivalent to 10 mg/dl is 0.85 Omega/mg/dl and 0.14 MHz/mg/dl, respectively. The sensitivity requirements reduce by about a factor 1.6, if for each subject an individual calibration is carried out. Depending on the measure and the calibration procedure, the required sensitivities are a factor 3-50 greater than those reported in the literature. Thus, in order to be operational in home-use conditions, the signal-to-noise ratio (S/N) of existing impedance-based monitoring platforms using RLC circuits need to be improved by about one order of magnitude. In order to make non-invasive glucose monitoring possible we, therefore, suggest some measures that may improve the S/N by the required factor.