Andreas Caduff

Impact of posture and fixation technique on impedance spectroscopy used for continuous and noninvasive glucose monitoring.

Impedance spectroscopy allows for the assessment of changes in the permittivity and conductivity of erythrocyte cell membranes, induced by blood glucose variations. This study was performed to evaluate the potential influence of motion-induced microvascular blood flow variations from different forearm postures on the PENDRA (Pendragon Medical AG, Zürich, Switzerland) signal. Fifteen volunteers without diabetes were included (seven female, eight male, mean +/- SD age 33.3 +/- 9.9 years, body mass index 24.8 +/- 3.0 kg/m(2)). PENDRA devices were fixed at both upper extremities with different fixation techniques (bracelet and adhesive tape). Standardized position changes of the upper extremities were performed to induce variations in cutaneous microcirculation, which were assessed by laser-Doppler-fluxmetry with different probe temperatures on the forearm. Changes in microcirculation were seen in some of the different motion procedures: supine to hanging, 61.1 +/- 29.9 arbitrary units (AU) to 46.2 +/- 24.8 AU at 37 degrees C and 15.9 +/- 13.0 AU to 13.4 +/- 10.1 at skin temperature (P < 0.01 for both probes); supine to upright, 80.5 +/- 55.4 AU to 74.9 +/- 43.8 AU (not significant) at 37 degrees C and 18.7 +/- 16.8 AU to 20.9 +/- 16.1 AU at skin temperature (P < 0.01). An initially observed subtle influence of microcirculation variations on the impedance signal was minimized when the device was fixed by both bracelet and tape. Other influencing factors (such as temperature, local anatomy, etc.) are addressed in the complex calibration procedure. Well-educated patients might be the best candidates for first using the device for continuous glucose monitoring. They may especially benefit from the trend indication and the hypoglycemia/hyperglycemia threshold and alarm functions.