12 - Cerebral Microcirculation

Abstract

This chapter focuses on cerebral microcirculation and discusses the pattern and possible regulatory mechanisms of blood flow in cortical capillaries as derived principally from observations with intravital microscopic techniques. Methods used to study the dynamics of flow through brain capillaries are direct and indirect; the latter is further subdivided into physiological and morphometric approaches. Indirect physiological techniques use intravascular indicators to determine transit time of red blood cells or plasma in the microcirculation, although not strictly in the capillary bed. Morphometric approaches detect steady-state differences in perfused capillary density. A novel technique that utilizes bolus injection of a plasma marker derives the distribution pattern of capillary plasma flow velocity from capillary filling in histological sections. Intravital microscopy provides the most direct assessment of flow in capillaries, although it is limited to a relatively shallow depth of cortical tissue. It is also possible to measure capillary flow velocity by tracking the movement of randomly occurring plasma gaps; however, this may introduce a bias into the measurement because plasma gaps are usually associated with the passage of slowly moving leukocytes.