CHAPTER
4
Hemodynamics
of
Large Arteries
4.1
Ventricular Outflow and the Aorta
4.1.1
Ventricular Ejection
Cardiac contraction which results in ventricular ejection
of
blood
flow into the aorta occurs in systole. This corresponds to the ejection
period during which the aortic valve is open (Fig. 4.1.1). This is preceded
by an isovolumic contraction period when the cardiac muscles develop
force and generate pressure, while the ventricular volume stays constant.
Only when the ventricular pressure exceeds the aortic pressure, the aortic
valve opens and ejection begins. Ventricular outflow is a function of the
rate of change of ventricular volume, i.e.
dV
Q=-
dt
(4.1.1)
Aorta is the principal receiving conduit and thus its properties play a
dominating role in ventricular ejection. Ventricular outflow is pulsatile,
due to the contractile apparatus of the ventricle. This pulsatility is
preserved due to the distensibility of the aorta and its branching arteries.
This pulsatility also implies that there is an oscillatory or pulsatile
contribution to the vascular load of the heart. Components of this load
are the resistance
(R),
compliance
(C)
and inertance
(L)
associated with
blood flow and vessel wall properties. It is recognized that aorta
contributes largely to the overall arterial system compliance. The greater
mass of blood ejected during systole, contributes to inertia, hence greater
overall inertance. To facilitate ventricular ejection, the aorta presents the
