Hemodynamics
of
Large Arteries
77
least amount of resistance. Thus, the aorta is principally responsible for
overall arterial system compliance and inertance, but less
so
for total
resistance.
Fig. 4.1.1
:
Simultaneously measured cardiac muscle segment length (top tracing),
left
ventricular pressure (LVP), aortic pressure (AoP) and aortic flow (Q). Ejection begins
when LVP exceeds AoP
and
ends with aortic valve closure. Cardiac muscle shortening
from end-diastole to end-systole is clearly shown.
It is important to know about the function
of
the heart as an energetic
mechanical pump.
To
this end, it suffices to understand the global
pressure-volume behavior in relation to cardiac muscle shortening and
force generation. This section first
looks
at factors that give rise to
ventricular ejection and then examine the factors that can modify this
ejection by the aorta and the rest of the arterial system. To accomplish
these, we begin with the dynamics
of
cardiac muscle contraction to
overall ventricular pumping mechanism, and the timing and duration of
the ejection. We will then look at the corresponding dynamic changes
that take place in the aorta and how these changes can significantly
modify ventricular outflow.
