Ambulatory monitoring of skin blood flow: the μHematron device

The study of skin blood flow (SBF) by measuring the thermal conductivity of living tissues is performed using a non-invasive Hematron sensor designed by A. Dittmar. This paper presents the design and realization of the instrumenta- tion (μHematron) associated with the Hematron probe. The miniaturization of the conditioning electronics was achieved using a Programmable System-on-Chip (PSoC™) component from Cypress Semiconductor Corporation. Validation of the μHematron device was done using analog reference condition- ing electronics. Experiments have been performed on a physi- cal model and under in-vivo conditions. Characteristics of the new instrument are promising, facilitating monitoring of skin blood flow under ambulatory conditions, thus enabling new monitoring applications 3 ). The new design of the associated electronics is based on a program- mable component, PSoC™ (2), with a view of reducing the number of external discrete components and thus minimiz- ing the hardware to facilitate ambulatory measurements by locating comfortably the total miniaturized system on the patient's wrist. Skin blood flow is determined by measuring thermal conductivity which is directly related to the tissue's thermal exchanges. These exchanges depend on the effective blood perfusion of the tissue and the thermal conductivity is con- sidered an indication of such tissue perfusion (3).