Design and validation of an ambulatory system for the measurement of the microcirculation in the capillaries: µHematron device

The non-invasive Hematron sensor is an active sensor used in studying skin blood flow (SBF) by measuring thermal conductivity of living tissues. Up to now, the Hematron device was composed of the Hematron probe and a heavy analog conditioning electronics. This paper presents the design, realization and validation of an ambulatory device (muHematron) associated with the original Hematron probe. The electronic architecture is based on a Programmable System on Chip (PSoC^trade), which contributes in reducing the number of discrete components, and consequently, the electronic conditioning circuit of Hematron. The muHematron device can be worn on the wrist of the patient thanks to its size (4times3times1 cm³) compared to the non-ambulatory conditioning electronics sized 20times30times20 cm³. In addition, data can be stored in a muSD card or transmitted using a ZigBee module. The validation of the muHematron device was performed using the analog conditioning electronics as a reference. Experiments were performed first on a physical model reproducing microcirculation in order to characterize the linearity of the thermal conductivity as a function of water flow. Then, two experiments were hold in-vivo conditions highlighting the performances of this new device. In a first experiment, effects of mental calculation on effective tissue perfusion were measured and in a second one, effects of an anti-cellulite cream on micro-vascularisation and skin temperature were studied.