Development of a system for monitoring the body surface circulation and its application. Part 1. Fundamental study

Abstract

The thermal diffusion method is based on a linear relationship between thermal conductivity of tissue and the tissue blood flow. Therefore, thermal diffusion is very sensitive to changes in tissue blood flow. However, it has been impossible to assess tissue blood flow quantitatively by this method. For the quantitative dynamic assessment of body surface circulation, a thermal diffusion flow probe incorporating a Peltier stack was used. In order to modify the apparatus using this probe for measuring body surface circulation continuously, fundamental studies about the measurement of human skin blood flow were carried out in the finger using the thermal diffusion method. The results obtained were as follow.1) The voltage difference of the thermocouples (V) of a probe placed on plates of various materials similar in the thermal conductivity to human skin was measured. A highly positive correlation between the thermal conductivity of the material and the reciprocal number of the voltage difference of the thermocouples (1/V) (r=0.973, p<0.001) could be observed. The use of this probe enabled us to assess the thermal conductivity of materials and tissues quantitatively.2) V gradually increased in parallel with the finger ischemia induced by inflation of a touniquet, suggesting that V varied with the change of finger blood flow and that its baseline was steady.3) A highly significant positive correlation was obtained between finger blood flow measured by the inhaled hydrogen clearance method (Hydrogeni FBF) and 1/V (r=0.949, p<0.001). V with no flow (V0) and constant Φ was estimated, and a calibrating line based on the following equation was determined.F=Φ(1/V-1/V0)Finger blood flow measured by the thermal diffusion method (Thermal FBF) was obtained. A highly significant positive correlation was obtained between Hydrogeni FBF and Thermal FBF (r=0.949, p<0.001).4) A highly significant positive correlation was obtained between finger blood flow measured by an electrochemically generated hydrogen clearance method (Hydrogene FBF) and 1/V (r=0.953, p<0.001). Calibration by this method was carried out taking account of the apparent flow by diffusion of hydrogen gas to the surrounding area (Diffusion Flow). A highly significant positive correlation was obtained between Hydrogene FBF subtracted Diffusion Flow and Thermal FBF (r=0.953, p<0.001).5) Thermal FBF calibrated by the electrochemically generated hydrogen clearance method almost agreed with that determined by the inhaled hydrogen clearance method in terms of the absolute value of the finger blood flow.Using the thermal diffusion method calibrated previously by the hydrogen clearance method in normal human subjects, the absolute value of skin blood flow can be measured continuously and noninvasively in humans. It was concluded that the apparatus for measuring skin blood flow continuously by the thermal diffusion method could be utilized as a monitor of the body surface circulation and was thus useful for diagnosis and research in various medical fields.