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(A) The PPG probe. Light is transmitted from the light-source (LED) through the fingertip to the photodetector (PD). (B) Some pulses of the original PPG signal: the changes in transmitted light intensity as a function of time, due to cardiac activity. Maximal transmitted light intensity occurs at end diastole, when the tissue blood volume is at a minimum. Vp is the voltage pulses measured by the photodetector PD.
