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1 Department of Bioengineering, University of California, San Diego, La Jolla, California, 92093-0412; and 2 Department of Polymer Chemistry, Advanced Research Institute for Science and Engineering, Waseda University, Tokyo 169-8555, Japan
The unanesthetized
hamster dorsal skinfold preparation was used to monitor diameters and
blood flow rates in resistance arteries (small arteries,
A0: diameter, 156 ± 23 µm)
and capacitance vessels (small veins,
V0: 365 ± 64 µm), during 45 min of hemorrhagic shock at 40 mmHg mean arterial pressure (MAP) and
resuscitation. A0 and
V0 vessels constricted
significantly to 52 and 70% of the basal values, respectively, whereas
precapillary arterioles
(A1-A4, 8-60 µm) and collecting venules
(VC-VL,
26-80 µm) did not change or tended to dilate. Blood
flow rates in the microvessels declined to <20% of the basal values.
Resuscitation with shed autologous blood (SAB) showed incomplete
recovery of A0 and
V0 diameters even 2 h after
resuscitation (71 ± 14% and 81 ± 18%, respectively, of basal
value), whereas other vessels did not change significantly. The
behavior of A0 diameter coincided
with the incomplete recovery of blood flow rates in all the vessels
(ca. 50%) according to Poiseuille's law, and the incomplete recovery
of functional capillary density (ca. 75%). Resuscitation with 8%
human serum albumin in saline (HSA) tended to show higher levels of
A0 constriction and A4 dilation and lowered blood flow
rates. Resuscitation with SAB restored tissue
PO2 27 ± 10 mmHg after 2 h, which
was near control levels (28 ± 5 mmHg), whereas resuscitation with HSA caused tissue PO2 to remain
significantly depressed (6 ± 2 mmHg), and flow rates were
significantly lower than resuscitation with SAB. These results indicate
that response of the A0 vessels is
the crucial determinant of blood flow in the observed area. The
constriction of A0 may help
sustain MAP, and constriction of
V0 may enhance blood
redistribution from the skin to the vital organs under the hypotensive condition.
feeding artery; vasoconstriction; autologous blood; albumin; microcirculation
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