The
Microcirculation
205
The circumferential stress-strain relation of microvessels follow the
curvilinear relations found arteries and veins, though to a greatly
different extent. The circumferential stress-strain relation of isolated
capillary blood vessels in gracilis muscle of Sprague-Dawley rats with
fascia removed
is
shown
in
Fig. 7.2.3. Here, the capillary wall is not in
contact with muscle fibers. The assumption is made that all the
circumferential tension is carried by the basement membrane.
It should be noted here that the diameters of microvascular vessels
change continuously throughout the cardiac cycle. Thus, the compliance
change must follow the nonlinear behavior as we have shown earlier for
the arteries.
In other words, the compliance
is
pressure-dependent
(Chapter 4), thus time-varying.
The measurements of diameters of
subendocardial arterioles and subendocardial venules by Kajiya and his
colleagues (Yada et al., 1993) support this conclusion (Fig. 7.2.4).
Arteriole
-
100
msec
0
70
1
E
5
50
Venule
End-diastole
1
t
End-systole
-
100
msec
0
Fig.
7.2.4:
Continuous variations
of
the diameters
of
a subendocardial arteriole and a
subendocardial venule throughout the cardiac cycle. From Yada et al.
(1993)
