Hernodynamics

of

Large Arteries

137

0.7

0.4

0.3

This increased stiffness has been suggested to be related to the structure

of the arterial wall. This implies that the compliance-pressure relation is

not a constant one. The declining arterial compliance with increasing

pressure has been observed in the central aorta and in individual arteries.

The inverse exponential relation between compliance and pressure for

the arterial system is shown in Fig. 4.5.8.

0.2

I

t

0.9169

Fig.

Compliance plotted against mean arterial blood pressure reflecting the

pressure-volume relation.

The relationship is nonlinear, implying that at higher

distending pressures the intraluminal volume change is smaller, resulting in a lower

compliance. The decrease in arterial compliance with increasing blood pressure follows a

negative exponential function.

nonlinear model of the arterial system incorporating a pressure-

dependent compliance element

(C(P))

is shown in Fig. 4.5.9 (Li et al.,

1990).

The model consists of the characteristic impedance of the

proximal aorta

(Z,),

the peripheral resistance

(Rs),

and

C(P).

The

compliance is exponentially related to pressure and is expressed as