Figure 1

Blood-vessel model illustration with hypothetical blood pulses: (a) DVP signal, (b) light intensity in the systolic phase, and (c) light intensity in the diastolic phase. The variables, \(d_{1}\) and \(d_{2}\) are the diameter of the blood-vessel when blood pulse enters the blood-vessel and leaves the vessel, respectively. In addition, the photodetector and light emitting diode are denoted as PD and LED, respectively in both (b,c).