In order to assess tissue blood flow quantitatively under various temperature conditions, we have developed a new blood-flow measurement apparatus based on the thermal diffusion method. This new method is hardly affected by environmental temperature, by means of using the thermal clearance curve with its baseline corrected before each measurement. Fundamental studies concerning the measurement of human skin blood flow were carried out in the finger. The results obtained were as follows.
1) The gradient of the thermal clearance curve did not show significant changes under various temperature conditions. This result indicated that the effects of environmental temperature on the thermal clearance curve were almost removed.
2) A highly positive correlation was obtained between the thermal conductivity of various materials similar to human skin in thermal conductivity and the gradient of the thermal clearance curve from a probe placed on a plate of each material.
3) There was linear relationship between the water flow and the gradient of the thermal clearance curve in various water flows of a micro-circulation model. The gradient of the thermal clearance curve obtained for each water flow had good reproducibility.
4) The gradient of the thermal clearance curve changed in parallel with the finger ischemia and hyperemia induced by inflation of a tourniquet. There was good reproducibility in continuous measurements.
5) A highly significant positive correlation was obtained between finger blood flow measured by the inhaled hydrogen clearance method and the gradient of the thermal clearance curve, indicating that it was possible to assess finger blood flow quantitatively by the gradient of the thermal clearance curve.
The weak point in the former thermal diffusion method, where the baseline was unstable as a result of environmental temperature, was removed. It was concluded that this new thermal diffusion method using the thermal clearance curve, which was calibrated previously by the hydrogen clearance method, enabled us to measure finger blood flow noninvasively at various temperatures. This method will be useful for diagnosis and research in various medical fields.
