新たな電気回路モデルによるパルスオキシメトリ誤差の検討

抄録

In the principle model of pulse oximetry, the measured absorbance change occurs by a thickness change of the arterial blood. However, we cannot explain the absorbance change of the tissue only by thickness change of the arterial blood when we consider these three phenomena of circulatory dynamics:1) arterial blood flows into the tissue as pulsatile flow, 2) Oxygen saturation decreases by oxygen consumption in the tissue, and 3) venous blood flows out from the tissue. In this study, we made a new electrical model of pulse oximetry and examined the mechanism of the absorbance change when the height of the hand is changed. We measured absorbance ratio and SpO₂ at three vertical hand positions, 1) on the table (middle), 2) rise over the head (up), 3) lowered (down), with six healthy volunteers. The absorbance ratios increased in the lowered hand position and there was an error to underestimate SpO₂. The mean ± SD of SpO₂ in the 6 subject at the middle, up, and down positions were 98.0 ± 1.28, 98.4 ± 0.84, 96.3 ± 1.69(%), respectively. We simulated pulse oximetry using our new electrical model, and we were able to express a mechanism to increase the absorbance ratio at the lowered hand position.