Figure 2.
Previous mathematical model of the oscillogram (Liu et al., 2016, 2017). (1) The envelope difference of the unmeasured arterial blood volume (V) vs. external pressure (Pe) function is equal to the difference in the x-axis reversed blood volume-transmural pressure relationships (f(P − Pe)) evaluated at P = Ps and P = Pd. (2) This envelope difference is equal to the envelope difference of the blood volume oscillation (V, i.e., high-pass filtered blood volume) vs. Pe function. (3) By assuming incompressible tissue around the artery and a linear and static cuff pressure-air volume relation, the latter envelope difference is proportional to the envelope difference of the measured oscillation (O) vs. Pe function (i.e., oscillogram) through a k (reciprocal of cuff compliance) scale factor. (The cuff-pressure-air volume relations shown are from two actual cuffs called dura_cuff and bladder_cuff.) (4) The oscillogram may thus be represented as O = kf(Ps − Pe) − kf(Pd − Pe).