Biomedical Engineering Reference
In-Depth Information
Fig. 4.2 A
: length-tension behaviors of swine carotid media, where maximal steady-state active
tension is obtained at a certain optimal length
L
0
.The
bottom curve
is the passive behavior, the
middle curve
is the active behavior and the
top curve
is the total behavior (passive and active)
(Kamm et al.,
1989
).
B
and
C
: active stress development and stretch behavior during isomet-
ric stimulation and isotonic shortening for two different after-loads (Dillon et al.,
1981
).
D
:two
force-velocity curves for isotonic quick-releases measured at 1 min and 10 min after isometric
contraction at optimal length (Dillon et al.,
1981
)
4.2.2 Length-Tension Relationship
Smooth muscle is able to generate active tension over a broad range of muscle
lengths. The active length-tension relationship has a parabolic behavior with max-
imal active tension at an optimal muscle length larger than the slack length, see
Fig.
4.2
A. In addition, Figs.
4.2
B and C show the respective active stress develop-
ment and stretch behavior during isometric stimulation and isotonic shortening for
two different after-loads.
The origin of the active length-tension behavior, also found in skeletal muscle, is
still not clearly distinguished but there are some hypothesis. One hypothesis is that
the agonist sensitivity may be dependent on the stretch of the smooth muscle (Rem-
bold and Murphy,
1990b
). When the
Ca
2
+
]
was measured for the same concen-
tration of agonist but at different muscle stretches, it was found that the magnitude
of initial behavior of
[
Ca
2
+
]
function was different for different muscle stretches.
Agonist stimulation (histamine, noradrenalin and so on) activates G protein-related
pathways which leads to an increase in intracellular
[
Ca
2
+
]
[
to be different from
