3: The physiology of hemodynamics: Metabolism and circulation

In order to better understand the intricacies of cerebral hemodynamics and the mechanisms behind neurovascular coupling, one must begin by understanding the many functions of blood and the circulatory system in large multicellular organisms such as ourselves. Therefore Chapter 3 begins by discussing basic mammalian physiology, with an emphasis on the vascular system. Blood rheology, vascular hydrodynamics and gas exchange are discussed in Section 3.2. The concepts of global and local hemodynamics are introduced in Sections 3.3 and 3.4 respectively, and Section 3.4 discusses the control of local blood flow in great detail, with emphasis on our current understanding of the neural and humoral influences on vascular function. Sources of biogenic interference are then presented in Section 3.5, and the concept of a biogenic noise floor is introduced and explained. Section 3.6 concludes the chapter with a discussion on the effect of wavelength and optode spacing on image contrast, and how judicious selection of the optical source wavelengths might be useful in optimizing DOT signal quality.