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Blood flow, capillary transit times, and tissue oxygenation: The centennial of capillary recruitment

Publikation: Bidrag til tidsskrift/Konferencebidrag i tidsskrift /Bidrag til avisReviewForskningpeer review

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The transport of oxygen between blood and tissue is limited by blood’s capillary transit time, understood as the time available for diffusion exchange before blood returns to the heart. If all capillaries contribute equally to tissue oxygenation at all times, this physical limitation would render vasodilation and increased blood flow insufficient means to meet increased metabolic demands in the heart, muscle, and other organs. In 1920, Danish physiologist August Krogh was awarded the Nobel Prize in Physiology or Medicine for his mathematical and quantitative, experimental demonstration of a solution to this conceptual problem: capillary recruitment, the active opening of previously closed capillaries to meet metabolic demands. Today, capillary recruitment is still mentioned in textbooks. When we suspect symptoms might represent hypoxia of a vascular origin, however, we search for relevant, flow-limiting conditions in our patients and rarely ascribe hypoxia or hypoxemia to short capillary transit times. This review describes how natural changes in capillary transit-time heterogeneity (CTH) and capillary hematocrit (HCT) across open capillaries during blood flow increases can account for a match of oxygen availability to metabolic demands in normal tissue. CTH and HCT depend on a number of factors: on blood properties, including plasma viscosity, the number, size, and deformability of blood cells, and blood cell interactions with capillary endothelium; on anatomical factors including glycocalyx, endothelial cells, basement membrane, and pericytes that affect the capillary diameter; and on any external compression. The review describes how risk factor- and disease-related changes in CTH and HCT interfere with flow-metabolism coupling and tissue oxygenation and discusses whether such capillary dysfunction contributes to vascular disease pathology.

OriginalsprogEngelsk
TidsskriftJournal of Applied Physiology
Vol/bind129
Nummer6
Sider (fra-til)1413-1421
Antal sider9
ISSN8750-7587
DOI
StatusUdgivet - 11 dec. 2020

Bibliografisk note

Funding Information:
This review was supported by the VELUX Foundation (ARCADIA II Grant 0026167) and a Lundbeck Foundation Professorship to the author (Grant R310-2018-3455).

Publisher Copyright:
Copyright © 2020 The Author

Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.

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