Hemodynamics

of

Large Arteries

heart during systole into the arterial system distends the large arteries,

primarily the aorta.

During diastole, the elastic recoil of these same

arteries propels blood to perfuse the smaller peripheral resistance vessels.

This initiated the earlier conceptual understanding that the distensibility

of

large arteries are

important in allowing the transformation of

intermittent outflow of the heart to steady outflow throughout the

peripheral vessels. In other words, the large overall "compliance" of the

large arteries protects the stiff peripheral vessels of organ vascular beds

from the large swing of blood pressure due to pulsations. This view is

still held by many until this day. The significance of arterial pulsations

remains a topic of debate.

The windkessel model is now credited to Frank (1 899) whose original

interest was in obtaining stroke volume from measured aortic pressure

pulse contour. Methods to derive flow from pressure measurement or the

so-termed pressure-derived flows

(Li, 1983) have continued to attract

considerable interest despite the advent of the electromagnetic blood

flow and ultrasonic blood velocity measuring devices.

psriphecy

Vssseis

Fig.

4.5.2:

Diagrammatic representation

of

the left ventricle and the arterial circulation

based on the idea

of

the windkessel. The ventricle ejects into a compliant chamber

representing the aorta, blood flow is stored in systole (solid line) and on elastic recoil in

diastole (dotted line), the stiff peripheral vessels are perfused.

In the analysis of the windkessel model, the amount of blood flow,

Qs,

stored during each contraction is the difference between inflow,

Qi

to

the large arteries

and

the outflow,

Qo,

the small peripheral vessel

(Fig.

Qo

(4.5.48)