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The John B. Pierce Laboratory and Department of Chemical Engineering, Yale University, New Haven, Connecticut 06519
Received 8 February 1996; accepted in final form 13 August 1996.
Emerson, Geoffrey G., and Steven S. Segal. Alignment of
microvascular units along skeletal muscle fibers of hamster retractor.
J. Appl. Physiol. 82(1): 42-48, 1997.
When muscle fibers contract, blood flow requirements increase
along their entire length. However, the organization of capillary
perfusion along muscle fibers is unclear. The microvascular unit (MVU)
is defined as a terminal arteriole and the group of capillaries it
supplies. We investigated whether neighboring MVUs along the fiber axis perfused the same group of muscle fibers by using the parallel-fibered retractor muscle. Hamsters were anesthetized and perfused with Microfil
to visualize MVUs relative to muscle fibers. Fields of study, which
encompassed five to seven neighboring MVUs along a muscle fiber, were
chosen from the interior of muscles and along muscle edges. On average,
MVUs were 1 mm in length, 0.50 mm in width, and 0.1 mm deep; segments
of ~30 fibers were contained in this tissue volume of 0.05 mm3 (20 MVUs/mg muscle). The total
distance across muscle fibers encompassed by a pair of MVUs is
designated "union" (U); the fraction of this distance common to
both MVUs is designated "intersection" (I). The ratio of I to U
for the widths of neighboring MVUs provides an index of MVU alignment
along muscle fibers (e.g., I/U = 1.0 indicates complete alignment,
where the fibers perfused by one MVU are the same as those perfused by
the neighboring MVU). We found that I/U along muscle edges (0.71 ± 0.02) was greater (P < 0.05) than
the ratio measured within muscles (0.66 ± 0.02). A model predicted
a maximum I/U of 0.58 with random MVU alignment. Thus measured values
were closer to random than to complete alignment. These findings
indicate that an increase in blood flow along muscle fibers requires
the perfusion of many MVUs and imply that vasodilation is coordinated
among the parent arterioles from which corresponding MVUs
arise.
arteriole; capillary; functional unit; local flow control; microcirculation
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