FIGURE 1.

The concept of pulse pressure components [22]. (a) Illustration of the distending arterial pressure (P) and volume (V) that stands also for cross-sectional lumen area, or lumen diameter. (b) and (c) show, respectively, a linear P–V and nonlinear P–V relationship. At each selected pressure (empty circle), stiffness is defined as the ratio between small incremental changes in P and V, so-called ‘tangent slope’, which is the tangent of the angle between the tangent to the curve, at that point, and the x-axis. Thus, in (b), stiffness is simply the slope of the line, characterizing a simple elastic tube having constant elasticity (‘elastic behavior’), whereas in (c), stiffness increases for higher pressure (or volume), characterizing the ‘stiffening behavior’ displayed by real arteries (see Introduction). (d) The variation of the distending arterial pressure from its diastolic level to systolic level (DBP to SBP, respectively) during the early systole, which is the pulse pressure (PP); the corresponding volume change (‘pulse volume’ ΔV), and the stiffness change from its ‘diastolic’ to ‘systolic’ level. This diagram enables to view, in general, the P–V relationship during the early systole, as a superposition of a linear relationship (‘elastic’) having the slope of the diastolic stiffness and a nonlinear relationship (the original P–V relationship minus the elastic relationship). This procedure splits a given PP into the illustrated ‘elastic component’ (elPP, equals to ΔV · [diastolic stiffness]), and a ‘stiffening component’ (stPP equals to PP-elPP) expressing the extra pressure required to overcome the increased resistance of the arterial wall because of the increased stiffness using the given formulas for quantitative determination of elPP and stPP (Supplemental Methods, http://links.lww.com/HJH/C43). PP, pulse pressure.