Summary
Blood flow in the microvasculature is assumed to be regulated by 2 independent mechanisms acting in series: arterioles, whose calibre controls the mean blood flow (b) through each perfused capillary, and precapillary sphincters, whose all-or-nothing behavior determines the number (n) or density of capillaries that are open and perfused. Neithern norb can be measured reliably, but the product can be estimated by the clearance rate of radioactive xenon injected into muscle. Radioiodide moves more slowly than Xe133 across capillary walls, and at high values ofb, its clearance rate is diffusion-limited, i.e., sensitive ton but not tob. Mixtures of Xe133 and I131-iodide were injected into the gastrocnemii of anesthetized cats, and the levels of both isotopes were monitored continously by an external scintillation probe. A theoretical equation relating these clearance rates ton andb adequately describes data derivated from experiments in whichb was altered by inducing changes in arterial blood pressure while attempts were made to paralyze vasomotor mechanisms in order to keepn constant. If the model is valid, the double clearance method makes it possible to partition any observed change in capillary blood flow into 2 parts, that due to Δb and that due to Δn. Because the method provides a measure of the product of capillary permeability and effective capillary surface area, it is also possible to ascribe any observed changes in this product to alterations in permeability.
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This study was supported in part by USPHS grant GM 11598 from the National Institute of General Medical Sciences.
Portions of these data have been reported before [Fed. Proc.25, 594 (1966)].
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Gosselin, R.E., Audino, L.F. Muscle blood flow and functional capillary density evaluated by isotope clearance. Pflugers Arch. 322, 197–216 (1971). https://doi.org/10.1007/BF00602070
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DOI: https://doi.org/10.1007/BF00602070