Measuring of oxygen saturation using pulse oximeter based on fuzzy logic

The pulse oximeter is the most used device due to be a noninvasive method in measuring the oxygen level in blood. In the pulse oximeter, red and IR (Infrared) LEDs (light emitting diode) sent signals to the photodiode. An equation or relationship between the ratio (R) of signals (red and IR) received by photodiode with the oxygen saturation value (SpO₂) needs to model the value of blood oxygen saturation. Normally, the calibration curve needs to create this equation. A calibration device is necessary to obtain this calibration curve. Since this device is very expensive, absorbation coefficients obtained from healthy individuals have been used both to create this curve and to decrease the cost of pulse oximeter. In this study, firstly, R (ratio) value is calculated according to absorption rates of signals, which are sent by red and IR LEDs in finger mounted oxygen saturation sensor. The obtained R value has been used as the input to fuzzy logic then SpO₂ value has been calculated. Also, a linear relationship between SpO₂ and R values has been created with absorption coefficients using linear regression method and compared with SpO₂ values calculated by fuzzy logic method. The results show that the SpO₂ values, which are calculated by fuzzy logic, are more reliable and healthy.