Wave separation
Several methods have been suggested to separate measured pressure and flow into forward and backward traveling components. This has been motivated by the notion that waves traveling from the heart toward the periphery contain information related to the heart, while the reflected waves contain information related to the periphery. The simplest method, which is still the method of choice for most applications, was suggested in [6]. This method is based on the linearized and inviscid form of the governing equations. $$ \begin{equation} p = p_f + p_b, \quad Q = Q_f + Q_b = \frac{p_f}{Z_c} - \frac{p_b}{Z_c} \end{equation} $$ which by simple algebraic elimination yield: $$ \begin{align} p_f &= \frac{p + Z_c \, Q}{2}, & p_b & = \frac{p - Z_c \, Q}{2} \tag{101} \\ Q_f &= \frac{Z_c \, Q + p}{2 Z_c}, & Q_b & = \frac{Z_c \, Q-p}{2 Z_c} \tag{102} \end{align} $$
In a normal healthy subject the reflections in the aorta come in the diastole after the aortic valve has closed. Thus, they are believed of enhance coronary perfusion. However, for elderly subjects with "stiffer" vessels the reflections may arrive in the systole. Thus, the reflections will increase the aortic systolic pressure and thereby increase the heart load. Such an condition may lead to hypertrophy.
Figure 9: A model of the human arterial system (from [7]).