Hernodynamics
of
Large
Arteries
79
length of the fiber, until the sarcomere reaches a length
of
about
2.2
pm,
the tension reaches a maximum and then declines as the length is
increased further. The extent of the overlapping filaments determines the
amount of force generation. This scheme is illustrated in Fig.
4.1.2.
The sarcomere tension-length relationship has been translated to the
intact global heart in terms of left ventricular developed pressure
(LVP)
and end-diastolic volume
(EDV).
The former is related to the developed
tension or force, while the latter is related to the initial muscle fiber
length
(lo)
or "preload".
100
-
T
Fig.
4.1.3:
Simultaneously measured regional tension and global ventricular in a dog left
ventricle. Notice the parallel relationship in the isovolumic phases.
The relation between sarcomere length
(I>
and left ventricular
volume
(V)
however,
is
not a linear one. This is expected, as the left
ventricle is non-cubical in shape. Thus, the percentage change in cardiac
muscle fiber length cannot be interpreted as a corresponding percentage
in left ventricular cavity volume. Even in the isovolumic ejection phase,
when the ventricular volume remains constant, cardiac muscle fibers at
different part of the ventricle may still be changing their lengths. Thus,
isovolumic (constant volume) contraction does not exactly correspond to
