Cell flow path influences transit time through striated muscle capillaries

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Abstract
Indirect estimates of erythrocyte transit time across capillary beds incorporate two assumptions, that the anatomically defined capillary length correctly describes the functional flow path taken by cells across the network, and that the distribution of perfused flow path lengths does not change during hyperemia. Direct measurements of cell flow paths through capillary networks, cell transit times, and associated blood flow variables, have been made using fluorescent erythrocytes as tracers of the total cell population. Observations were made in cremaster muscles from juvenile or adult anesthetized golden hamsters; these tissues have capillary networks of differing degrees of branching. In the juvenile (more branching) networks, mean functional flow path (Lf) was 351 +/- 6 (SE) micron, about twice the average distance from terminal arteriole to collecting venule (172 +/- 37 microns). In the less branching adult networks, Lf = 438 +/- 9 microns compared with the anatomically defined distance of 372 +/- 33 microns. In both groups, Lf distribution was unchanged during hyperemia produced by 10(-4) M adenosine. Directly measured cell transit times across the networks were longer than expected from previous indirect estimates: means were 3.2 +/- 0.1 s in juveniles and 4.2 +/- 0.2 s in adults, with decreases to 2.2 +/- 0.1 and 2.3 +/- 0.1 s, respectively, in hyperemia.