Analysis of Plethysmogram signal with transmittance and reflectance method

Photoplethysmography (PPG) is a non-invasive technique for measuring changes in volume within an organ or whole body. The information from this blood volume change signal can be used to calculate beats per minute (BPM) because each peak of the wave that occurred is correlated with one heartbeat. There are two sensor placement methods for PPG signals: transmittance and reflectance. The transmittance method is signified when the infrared and photodiode face each other, while in the reflectance, the infrared and photodiode are placed in parallel. The signal data from the finger sensor transmittance method and reflectance method are processed by analog signal conditioning using a bandpass filter frequency of 2.3Hz-2.5Hz, which is sent to the microcontroller to produce the BPM value and be displayed on Delphi. The PPG signal was compared by employing the transmittance and reflectance methods. The research concludes that the transmittance method produces a PPG signal with a sensitivity and specificity value of 96%, while the reflectance method produces a sensitivity and specificity value of 92%. The results indicated that the transmittance mode was more sensitive to blood pulses because the amplitude transmittance was higher than that of the reflectance mode.