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. 2015 May 21;5:10494. doi: 10.1038/srep10494

Figure 4. Simplified diagram of the new concept of the PPG signal formation.

Figure 4

(a) A part of the artery, which is situated near the dermis, in the diastole phase; (b) the artery in the systole phase in the case of free skin surface; (c) the systole phase in the case of the skin contact with the glass. Note that the density of vessels in the microcirculatory bed is the lowest in (a) and the highest in (c). The figure was drawn by I.S.