Development of a hybrid microwave-optical thermoregulation monitor for the muscle.

This paper presents the latest development of the hybrid microwave-optical thermoregulation monitor for the muscle. It is capable of warming the muscle and measuring the subsequent blood volume changes, using a novel microwave applicator with integrated optical probes. The challenge is to measure the thermoregulation response in deep tissue while minimizing any effect from the skin layer. We have introduced a skin cooling device, an additional integrated optical Laser Doppler flow monitoring probe and a temperature sensor to measure skin blood flow and temperature, respectively. The result shows that skin cooling is essential to minimize skin flow changes during microwave warming. The hybrid probe was placed on a human thigh to measure oxy/deoxy/total haemoglobin concentration changes (ΔHbO₂/ΔHHb/ΔHbT), skin flux and temperature upon microwave warming. Without skin cooling, the skin temperature was elevated by 4 °C and both ΔHbO₂/ΔHbT and skin flux increased, showing microwave warming occurring in both the skin and muscle. With skin cooling, the skin temperature was kept relatively constant. While ΔHbO₂/ΔHbT increased, the skin flux was relatively stable, showing a preferential microwave warming in the muscle, rather than the skin.