Abstract
| A bioimpedance transducer is proposed for noninvasive monitoring of insulin bioavailability after subcutaneous
injection. The insulin bioavailability is assessed indirectly by
measuring the local impedance variation due to the drug disappearance from the injection volume. The instrument allows to
manage the extreme variability in insulin response by patients
with diabetes due to skin conditions and/or alterations such as
lipodystrophy. In this way, the transducer can also be considered
as a key component for new generation of artificial pancreas. The
instrument achieves the state-of-the-art accuracy and uncertainty.
Intraindividual reproducibility also improved with respect to
previous studies. Moreover, the feasibility of an absorption
measurement is proven. After presenting the concept design
and the prototype, the metrological characterization during:
1) laboratory (on passive electrical components); 2) in vitro (on
eggplants); and 3) in vivo (on a human subject) experiments
is reported. In laboratory tests, typical percentage deterministic
errors of 1% on magnitude and phase were obtained. The mean
1-σ repeatability of 0.05% was obtained for both impedance
magnitude and phase. The in vitro tests were aimed to improve
the reproducibility by comparing the electrical behavior of
insulin and vehicle in eggplants. During in vivo tests, a decrease
in percentage 1-σ intraindividual reproducibility was reported
with respect to the state-of-the-art (from more than 200% to
36%), as the impedance magnitude is concerned. In a clinical
application framework, an accuracy of 9 µl was obtained by
means of a second-order polynomial model. The uncertainty was
4.2 µl, well below the typical volume of one insulin unit (10.0 µl). |