The
Microcirculation
203
measurement
of
pressure and velocity in a cat mesentery microvascular
bed. Arterial to venous distribution
of
the pressure and velocity is shown.
Pressure dropped rapidly in small arterioles, but more gradually in the
capillaries. The velocity drop parallels the velocity in the arterioles, not
so
in the venous side.
PRESSURE
-VELOCITY DISTRIBUTION
PRESSURE
-
mmHg
VELOCITY
-
mmlsec
VENOUS
MESENTERY
CAT
o
vEiocirr
PRESSURE
0
..
I"
lIIIII,,IIIIIIlIIII11111111
56
40
40
32
24
16
0
16
24
32
40
40
56
VESSEL DIAMETER-
micro
Fig.
7.2.1:
Illustration
of
arterial to venous distribution of intravascular pressure and
velocity in the cat mesentery as a function of microvessel diameters. Solid lines are fitted
curves. From Zweifach and Lipowsky
(1977).
The pressure gradient, Ap/Az or dp/dL can be measured by the micro-
occlusion technique.
Here,
two
pressure probes are inserted into
two
side branches
of
a
given vessel and
flow
is occluded in these side
branches. The
two
pressure readings divided by the distance between the
two
measurement sites gives the pressure gradient.
Lee and Schmid-Shonbein
(1
995)
have estimated distensibility
of
capillaries in skeletal muscles based on the pressure-area relation (see
Chapter
2).
They made
a
comparison
of
capillary distensibility when the
